GEOMATICS & VOCABULARY

MATERIAŁY DYDAKTYCZNE DO PRZEDMIOTU GEOMATICS & VOCABULARY Training and Project Materials Wydział Inżynierii Środowiska, Geomatyki i Energetyki Opracował - Ryszard Florek Paszkowski 1 / 65

CONTENTS 1. THE GEOMETRIC AND INTERPRETATIVE ASPECTS OF MICROSCOPE STEREOPHOTOGRAMMETRY 2 1.1. The basic theory of electron microscope 3 1.2. Description of a simple microscope electron gun 5 1.3. SEM and photogrammetry 8 1.4. SEM users and photogrammetrists 10 1.5. Similarities and differences between transmission and scanning electron microscopes 10 1.6. Production of stereo micrographs 12 1.7. Remarks on tilt angles 18 1.8. Distortions which affect a micrograph image 19 1.9. Importance of microscope calibration 23 1.10. Final conclusions 23 2. PHOTOGRAMMETRIC MAPPING OF THE ARCHEOLOGICAL SITE WITH THE USE OF AIR-PHOTOGRAPHS AND DIGITAL STEREO RESTITUTORS 25 2.1. Introduction 25 2.2. Terrestrial photos with respect to archaeology 30 2.3. Aerial photos with respect to archaeology 36 2.4. Stereo restitution with digital photogrammetric station Leica DVP 50 2.5. Problems experienced with the research 52 2.6. Conclusions and recommendations 53 3. A COMPARISION OF A METRIC AND NON-METRIC CAMERA FOR THE PURPOSE OF DOCUMENTATION OF BUILDINGS 55 3.1. Introduction 55 3.2. Major characteristics of metric and non-metric cameras 57 3.3. Documentation of buildings 57 3.4. Review of applications of documentation of buildings 58 3.5. Applications of photogrammetry and surveying for the documentation of buildings 60 3.6. Conclusions 65 2 / 65

1. THE GEOMETRIC AND INTERPRETATIVE ASPECTS OF MICROSCOPE STEREOPHOTOGRAMMETRY Users of Scanning Electron Microscopes seldom apply stereo measurements to the data which they obtain from the SEM. The Scanning Electron Microscopes which are utilized are often not calibrated properly, therefore the necessary corrections are not known (Florek 1994). These investigations were performed as a result of the cooperation within University of Cape Town between the Electron Microscope Unit and the Department of Surveying and Geodetic Engineering, namely between Prof. T Sewell and Dr. R Florek. The object of this work was to evaluate the accuracy of the StereoScan 440 Scanning Electron Microscope which has been purchased by UCT for the Electron Microscope Unit. The accuracy of the instrument needs to be known as many users extract information from the micrographs which a Scanning Electron Microscope produces. For the accuracy of the SEM to be determined it was necessary that a number of different magnifications were utilized. For this purpose the magnifications chosen were 250x, l000x and 10 000x. The following topics are presented: 1) The basic principles surrounding Electron Microscopes and especially the Scanning Electron Microscope. The manner in which one creates a stereo pair of micrographs. 2) A discussion of the various calibration techniques and the manner in which these techniques are utilized to determine the accuracy of the data obtained from the StereoScan 440. 3) The distortion parameters associated with the micrograph images, taken by the StereoScan 440. 4) An application in which stereo microscopy can be used with the StereoScan 440. The application undertaken was a brief analysis of Ferritic Stainless Steel, in which the Department of Materials Engineering at UCT is interested. 1.1. THE BASIC THEORY OF ELECTRON MICROSCOPE This chapter serves as an introduction to the subject of stereo electron micrography. It can provide the basis for further, more detailed studies into some of the areas of stereo electron microscopy. The chapter covers such topics as: 1) principles of the electron microscope; 2) selection of micrographs (electron microscope photographs) to create stereo images; 3) distortions which affect a micrograph; 4) theory and procedures to be followed in order to calculate 3-dimensional coordinates of points on a specimen, and 5) recommendations to improve the accuracy of the calculated coordinates. The very common and well known forms of photogrammetry are terrestrial and close range photogrammetry. Pictures of large objects are taken from a distance, not only from an airplane but also from a ground station or even from a satellite. These photographs are at a very small scale. If a user wished to photograph a small object at a larger scale, a camera fitted with macro lenses or special 3 / 65

devices could be used. Users were able to achieve photographs with a magnification of around 3x. At first, the cameras were partial metric cameras, but more recently CCD cameras have also been used. Characteristics OLM TEM SEM Lens System Glass or Quartz Electromagnetic Electromagnetic Image Display Eye Retina or Film Fluorescent viewing CRT for viewing and plate or film photography Energy Uses radiation from Thermonic emission UV through visible of electrons which spectrum to IR are accelerated by 50 to loookv Wave Lengths 200-700 nm > 0.1 nm > 0.1 nm Resolution 100 nm 0.3 nm 3.0 nm Depth of Field Poor Good Excellent Sample Requirements Thin Sections 0.1 - lyccm thick sections or only replica, 2-3 mm in diameter Magnification 15x - 3000x loox - 500 OOOx (stepped) Tab. 1.1. Comparison of OLM, TEM and SEM Thermonic emission of electrons which are accelerated by 1 to 30kV There is no thickness limit. Non-Metals (better) metal coated (Au, Pd or Al) up to 25 mm in diameter lox - 200 OOOx (continuous) Work which needs even greater magnification and larger scales requires the use of an optical light microscope. By fitting a camera to the microscope, photographs at magnifications up to 3000x are possible. If even greater magnification is required, electron microscopes are the only instruments capable of satisfying the user. Magnifications of up to 200,000x or 500,000x are possible depending on the type of electron microscope used. Electron microscopes have given scientists greater detection and were ever previously obtainable with optical light microscopes (OLMs). They have become indispensable in the fields of microbiology, metallurgy, criminology, microelectronics and many other sciences. For most users, single, two-dimensional micrographs (electron microscope photographs) have been suitable for their requirements. These users are generally interested in their micrograph's descriptive qualities and they only require low accuracy measurements of their specimens, if any. There is however, a growing demand for highly accurate, three-dimensional information of microscopic objects. These measurements can only be made from stereo pairs of micrographs. In most instances, this appears to be no more than a microscopic version of the macroscopic examples with which photogrammetrist regularly deals. However, the projection geometry as well as certain deformations, are different in electron microscopes than in any other photogrammetric situations (Ghosh 1989). Standard photogrammetric procedures can be applied if certain modifications are made to the measurement process and certain corrections are applied during calculations. There are two distinct types of electron microscopes; Scanning Electron Microscopes (SEM) and Transmission Electron Microscopes (TEM). Both can be used to create stereo micrographs and to measure three-dimensional characteristics of specimens. A distinction between the two will be made in a later part. This chapter can be broadly divided into two areas: I. the study of the production of a pair of stereo micrographs. II. the study of the measurement of micrographs to provide three-dimensional coordinates of points on the specimen. 4 / 65

These two areas can be further subdivided to investigate: 1) how a scanning electron microscope functions. 2) the procedures involved in obtaining a stereo pair of micrographs. 3) the effects that various degrees of rotation of the specimen stage have on the stereo effect of the micrographs. 4) the geometry of electron micrographs. 5) distortions to the micrographs. 6) procedures to measure the micrographs. 7) factors affecting measurement accuracy. For the purpose of studying the effects of stage rotation, micrographs of ostracods (bivalved micro crustaceans) at 200x and 500x were used.the micrographs were produced using a JEOL JSM-5200 scanning electron microscope at the South African Museum in Cape Town shown in Fig. 1.1. Fig. 1.1. The JEOL JSM-5200 scanning electron microscope Electron microscopes are used in preference to Optical Light Microscopes when very small objects need to be examined. An electron microscope offers greater resolutions at higher magnifications than optical light microscopes. This is possible because the method by which electron microscopes create an image of a specimen is different from the way in which optical light microscopes do. The fundamental principles behind electron and optical microscopes are similar. In both optical and electron microscopes, the specimen is illuminated by a form of radiation. This radiation interacts in some way with the specimen. The resulting radiation that is transmitted or reflected by the specimen is detected by a sensor and an image of the specimen is formed. The main differences between the principles of electron and optical microscopes, lie in the source of the radiation, how it is controlled, and how it is later detected by a sensor to form an image. The illuminating radiation in an optical light microscope is visible light emitted from a bulb. The light is controlled by optical lenses and directed towards the specimen. Once it has interacted with the specimen, the light is detected by a camera or the operator's eye. The illuminating radiation of an electron microscope is a beam of electrons emitted from an electron gun. This necessitates a different method of focusing the radiation than in optical light microscopes. Instead of optical lenses, magnetic lenses are used to direct the electron beam. Once the electron beam has interacted with the specimen, transmitted or reflected electrons cause an image to be formed on a screen. The remainder of this chapter will deal with two of the main differences between optical and electron microscopes; the electron gun and magnetic lenses. 1.2. DESCRIPTION OF A SIMPLE MICROSCOPE ELECTRON GUN The simplest electron gun consists of three components shown in Fig. 1.2.: 5 / 65

the filament - f the shield s the anode a, Fig. 1.2. The three components of a simple electron gun 1.2.1. Filament The filament in its simplest form is usually a V-shaped piece of wire. It is very thin, about 0.1 mm in diameter, and can therefore be electrically heated to incandescence. When a current is passed through the wire, the tip of the V becomes the hottest part of the filament and therefore the greatest source of electrons. This method of causing the filament to discharge electrons makes the filament a thermionic cathode. There are two characteristics which determine the suitability of a metal for use as a filament. The first is that the metal must have a low work function (measured in volts); it must supply a large number of electrons at as low a temperature as possible. Secondly, it must have a long working life. The working life of the filament can be extended by preventing oxidation and evaporation of the metal when it is heated up. This is done by heating the wire just high enough to provide satisfactory electron emission. Tungsten is the metal most commonly used since it has all the necessary properties. However, although the operating temperature is kept as low as possible, it is still near enough to the boiling point of the metal to cause some evaporation. This results in an average filament life of 15-40 hours (Wischnitzer 1970). 1.2.2. Shield The shield is a cylinder, with an aperture, which is in front of, and centered over the tip of the filament. The aperture is usually 1-3 mm in diameter (Wischnitzer 1970). The shield helps to ensure that only a narrow beam of electrons leaves the electron gun. 6 / 65

1.2.3. Anode The anode is a disk with an aperture in its center. The anode is grounded and attached to the positive terminal of the power supply. The rest of the microscope is also grounded. The cathode (filament) is therefore held at a large negative potential with respect to the anode and the microscope. This causes electron to be accelerated from the cathode towards the anode, through the aperture and down the column of the microscope. The path of the electrons is controlled by magnetic lenses. In reality, the operation of the electron gun is more complicated than has been mentioned in this section. However, although various types of electron guns have been developed and refined, they all share the same basic principles. 1.2.4. THEORY OF MAGNETIC LENSES In 1924, de Broglie proposed a hypothesis of the wave nature of a beam of moving electrons. He stated that the wavelength of the beam was dependent on the potential through which it had been accelerated. It later became apparent that if electron beams could be accelerated to a high velocity, then their small wavelength would make them suitable for illuminating microscopic objects. The small wave length (slightly greater than 0.1 nm) of electron beams would make them capable of providing a high resolution. Although de Broglie's hypothesis indicated the potential of electron beams, he did not propose ways in which electron beams could be controlled. In 1926, Busch stated that a magnetic field could be used as a lens for an electron beam (cited in Wischnitzer 1970). If a single electron enters a large magnetic field perpendicularly, the force of the magnetic field will cause the electron to move in a circular path. Should the electron escape the magnetic field, its velocity will be the same as on entering the magnetic field. An electron which moves parallel to a magnetic field will not be affected or deviated in any way. Fig. 1.3. Electron vectors in a magnetic field The theory can be developed further when the magnetic field is created by a solenoid. A solenoid's magnetic field not only runs from one end to the other, but also circles the solenoid. When an electron passes at a slight angle through the magnetic field of a solenoid, the electron's path will have two components (or vectors) with respect to the solenoid's magnetic field. 7 / 65

One of the electron's components is parallel to the magnetic field which runs the length of the solenoid. The other vector is at right angles to the magnetic field which circles the solenoid shown in Fig. 1.3 where V electrons initial path, V1 parallel component, V2 perpendicular component. The magnetic field has no effect on the vector that is parallel to the magnetic field; the vector remains constant and parallel to the long axis of the solenoid. The vector at right angles to the magnetic field causes the electron to move in a circular path. The combined effect of these two components is to cause the electron to trace a path which is a spiral. The axis about which the electron will spiral is an extension of the axis which runs lengthways through the solenoid. The spiral is ever decreasing, so the electron converges on the axis at a set distance from the solenoid. In reality, there are many electrons in an electron beam. The effect of the solenoid is to force the electrons into a narrow, focused beam at a set distance from the solenoid. The solenoid acts as a magnetic lens. The lens can be used to direct a narrow, high intensity beam or to magnify a narrow beam. By adjusting the strength of the magnetic field, the focusing point of the magnetic lens can be shifted. Magnetic lenses allows the electron beam within an electron microscope to be controlled and directed towards the specimen. First serial scanning electron microscopes were made by Cambridge Scientific Instruments Ltd. in 1965 and Japan Electron Optics Laboratory Ltd. (JEOL) in 1966. Scanning electron microscopes (SEM) have become well known research instruments for scientists in many domains. However, users of SEM techniques surprisingly seldom apply stereo photogrammetric methods for interpretation and measurement of geometric data. The procedures of stereophotogrammetric recording, interpreting and measuring, whilst conceptionaly easy, are not widely accepted by SEM users. They still continue to obtain third height Z co-ordinate by approximate methods which are less accurate and more uncertain. The experiments has been performed using Cambridge, JEOL and Tesla SEM microscopes in cooperation with different professions. e.g. from metallurgy, material engineering, biology, crystallography and criminology. The conclusions on problems of implementation of photogrammetric methods to SEM users research tools, are discussed in this chapter. 1.3. SEM AND PHOTOGRAMMETRY The SEM imagery can be characterized by an excellent depth of field. By tilting the specimen, the stereo micrographs pairs may be produced in perspective or almost parallel projection, depending on the image magnification. The angle of tilt of the specimen depends on many factors and sometimes the optimal value can be found to be out of the expected range. One of the major problems in using SEMs for stereo photogrammetric measurements is the need for accurate measurement of the tilt angle of the specimen stage. It can be solved by applying an optical level (Boyde, Ross) or other devices with satisfactory accuracies about 30''- 60". The TEM imagery taken with the transmission electron microscope can also be arranged in stereo mode, but depth of field is significantly limited by the nature of TEM. A procedure of analytical self-calibration of SEM was developed to solve for the tilt, rotation, magnification and systematic distortion parameters, in the department of Geodetic Science, Ohio State University (Ghosh, 1975). A new "spiral" distortion, resulting from non-linear electron scanning, was mathematically defined, in addition to an affine deformation, radial and tangential distortions (Maune). The accuracy of 3D coordinates obtainable from a given photogrammetric procedure depends on: stability of the system, observational error, geometry of intersection (angle of convergence), image 8 / 65

quality, shape of the object and the kind of instrument applied for observations (Ghosh, Nagaraja, 1976). More information can be obtained by using the combination of stereo models with TEM and SEM. Image quality obtainable from the TEM is very high, while the resolving power of the SEM is a limiting factor in the data acquisition (Ghosh et al, 1978, 1980). The SEM and TEM micrographs can be visualized as analogous to digital or ordinary photographs and X-ray images respectively. By combining their features in 3-D for the same sample object, the scientist would obtain information which is impossible with any other system. Data captured from a SEM stereo model represents the surface features of the object while data from TEM plotting reveals the internal structure of the object (Elghazali 1984a). Together, SEM and TEM, they offer a unique tool of complete analysis of micro objects. Elghazali (1984b) presented the mathematical models together with results of system calibration for the SEM micrographs. In regard to SEM applications, the author carried out or supervised some projects concerning SEM stereo photogrammetry: 1) Stereo-photogrammetric analysis of the topography of the surface of mill balls whilst being abraded; stereo micrographs taken with SEM JEOL 50A (Florek, et al, 1977 and research reports); 2) An investigation of the metallurgic fracture of steel thermally processed; on the base of micrographs taken with SEM Cambridge Stereoscan S4-10 (research project and supervised by Dr Florek thesis: Szpak & Szwaja); 3) An Application of stereo SEM to an investigation of the crystallographic processing of analcym Na(AlSi 2 O 6) H 2 O; micrographs taken from SEM Tesla BS-300; 4) A stereophotogrammetric analysis of cell membrane structures of frog cardiac myocytes in freeze-fracture replicas (Kordylewski & Florek, 1990); 5) One of the objectives of the thesis project (Dingle, 1993) was to determine the relative coordinates of selected points of a specimen. This work was carried out with assistance from the marine micropalaeontology unit of the South African museum in Cape Town. The specimens selected were ostracods (sea shell approximately 500 micrometers in length). A JEOL JSM-5200 SEM was used to create the images. An overall discription of systems and applications of electron microscopy is published in chapter 13, Non - Topographic Photogrammetry (Ghosh, 1989). There are seven contributions recommended for meaningful three-dimensional mapping with SEM micrography. These concern: a) magnification & parallactic angle; b) distortions in the micrographs; c) mathematical model; d) taking a pair of micrographs; e) instrumental /digital orientations; f) x,y,z digital or plotted output; g) other necessary data output. Should the following two points also not be considered 1) analysis of reliability of specimen; 2) an interpretation study of images, before one commence any measurements? 9 / 65

A new tool for scientists, the atomic force microscope AFM, may be used in association with TEM, to examine the same identified details of specimen. It allows comparison of the surface topography by both techniques (Kordylewski et al, 1994). At the other extreme, macro photographic methods offer a range of magnification 1:1 to 25:1, which are still best for some projects. 1.4. SEM USERS AND PHOTOGRAMMETRISTS The reasons why stereo photogrammetric analysis of SEM micrographs has not become very popular is not only the lack of suitable instruments but because of the lack of realization of SEM users to that possibility as well as weak inter field cooperation. Photogrammetrists involved in SEM projects solve geometric, and seldom interpretive aspects, using their air survey and close range photogrammetry background. They do not see the problems from the SEM user point of view and they present tendency to exaggerate the problem of measurement accuracy whilst neglecting the reliability of their data source. Often, comparative study, preliminary or relative results are most important. Unfortunately, when an interpretative aspect is neglected then precise and corrected measurements may be derived from wrong data source. The accuracy of the final results is not only affected by the work specifically undertaken by the photogrammetrist. The high accuracy of the measuring instruments available to the photogrammetrist may lead us to believe that provided we exercise extreme care and apply any corrections applicable to the measuring machine, extremely accurate relative coordinates of points on the object can be obtained. However, the stereo pair of images which the photogrammetrist works with are the end product of a long process in which the specimens are selected, prepared and photographed or recorded digitally. This process offers many opportunities to devalue the accuracy claimed by the photogrammetrist. The images should be suitable for photogrammetric measuring. There should be sufficient contrast and resolution to enable the photogrammetrist to distinguish between the points to be measured and their surroundings. In most cases SEMs are used to produce paper prints; however, the photogrammetrist requires the negatives or digital records. In order to produce negatives which are suitable to measure from, the contrast of the SEM screen and camera setting may need to be different from what would usually be used. It is important that the regular SEM operator be made aware of this. Within the SEM, distortions can occur due to the nature of the electron beam itself as well as due to the way in which the electron signal is amplified for the purpose of magnification. If these distortions are not predetermined and corrected for by the photogrammetrist, it is pointless for the photogrammetrist to strive for a exceptionally high accuracy. The calibration data can usually only be obtained for a microscope if a person with photogrammetric knowledge carries out an extensive calibration of the SEM (the camera and the SEM should be seen for this purpose as a single unit, not two separate parts of a system). It would be unlikely that a photogrammetrist provided with stereo images from, for instance, a geology department, could expect to be provided with calibration data of the SEM used. Furthermore, unless the SEM is specifically designed with stereo microscopy in mind, it is likely that the camera and film will be both fairly standard and will introduce distortions of their own to the image. The selection and preparation of the specimen has an effect on the final obtainable accuracies. If the specimen is dirty, it may be difficult under high magnification to distinguish between dirt and the specimen's features. 10 / 65

1.5. SIMILARITIES AND DIFFERENCIES BETWEEN TRANSMISSION AND SCANNING ELECTRON MICROSCOPES As was mentioned previously, there are two different types of electron microscopes; the transmission electron microscope TEM and the scanning electron microscope SEM. The two microscopes employ different principles to produce their images, and therefore produce different types of images with different applications. Although the transmission electron microscope is not the subject of this thesis, a differentiation between the two different types of microscopes is desirable. 1.5.1. Similarities between transmission and scanning microscopes The two types of electron microscopes have certain features in common. In both types of electron microscopes the specimen is placed on a specimen stage inside the microscope. This stage can generally be rotated in all three axis. The specimen on the stage is then illuminated by an electron beam generated from an electron gun. The complete path of the electrons needs to be free of any interference except that caused by the specimen. Consequently, the interior of the microscope needs to be exhausted to remove vapors and gas. A near total vacuum must be created by pumps and valves attached to the microscope. Special care also needs to be taken in the selection of the material for the stage to hold the specimen. The material should not be of a type that will cause excessive scattering of electrons. If this occurs, it may be difficult to distinguish between the stage and the specimen in the final image (Ghosh 1988). 1.5.2. Differences between transmission and scanning microscopes Two basic operating principles of Transmission Electron Microscope are as follows: 1) An electron beam is allowed to impinge upon the specimen. The specimen is a very thin (0.1/µm to 1.0/µm) slice of the sample. This is to allow the electron beam to pass through the specimen. As the electron beam passes through the specimen the electrons are scattered. 2) The final image is a measure of the scattering power of each point of the specimen. The image is formed by a magnetic objective lens, magnified and then displayed on a fluorescent screen. Operating principles of Scanning Electron Microscope are: 1) An electron beam is allowed to strike the specimen, but because the beam has less strength than that in a transmission electron microscope, and because the specimen is far thicker, the electrons do not pass through the specimen. 2) The beam of electrons is moved over the specimen in a grid like pattern by a scan generator (hence the name scanning electron microscope). The electron beam interacts with the surface of the specimen to produce various signals. 3) One of these signals is a beam of secondary electrons. These are electrons which are released from the atoms of the specimens surface (Ghosh 1989). These secondary electrons are drawn to a collector which has a positive charge. The collector is also known as an electron probe. 11 / 65

4) The image which is formed on a cathode ray tube is a measure of the strength of the secondary electron beam after it has been amplified. The strength of the secondary electron beam is a function of the angle between each point on the specimen and the primary electron beam. The image of the specimen is built up point by point; each scan of the electron beam adding to the image. Fig. 1.4 Representation of how the major components of an electron microscope work together. The different methods by which transmission and scanning electron microscopes form their images result in different types of images. A transmission electron microscope penetrates through the specimen resulting in an image which is similar to an X-ray. Transmission electron microscopes are capable of greater resolution at greater magnifications than scanning electron microscopes. A scanning electron microscope shows surface the detail of a specimen. They are capable of magnifications greater than 100,000x. They have good depth of field and resolution at even these magnifications. This gives them great potential for forming stereo pairs to carry out three-dimensional measurements of the surface of microscopic specimens. 1.6. PRODUCTION OF STEREO MICROGRAPHS This chapter describes the procedure followed for the production of a pair of stereo micrographs from a specimen within a scanning electron microscope SEM. A series of micrographs was produced to study the influence of specimen stage rotation on the quality of the stereo effect of pairs of micrographs. The results of this study will be presented in the next chapter. The specimens photographed are ostracods which are being studied and researched at the South African Museum. The researchers view stereo pairs of micrographs to interpret the surface of the ostracods. Although the specimens which were photographed are ostracods, the general technique is applicable to virtually all other types of specimens. Ostracods belong to the class Crustacea and live on the sea floor. They are bi-valves which gives them a certain external similarity to clams, but the creature which lives inside is more analogous to a crab. Fig. 1.5 is intended to give the reader an impression of how the creature stood. Although they occur abundantly in the modern world, the specimens which are being studied by the museum are approximately 20 million years old. 12 / 65

Fig. 1.5. Representation of a living ostracod. The object of study shown in fig. 1.6 is merely one of the outer shells of the creature. The soft internal parts having long since been destroyed. Different species have different shell features and shapes and range in length from 300 µm to 2 mm. Fig. 1.6. Left hand valve of an Ostracod. 13 / 65

1.6.1. Stereo pairs production steps. 1) The first step in the production of a good micrograph is to select a suitable specimen. The specimen should be as clean as possible since specks of dust or dirt will be clearly visible under high magnification. Even single crystals of dirt can be enough to obscure certain features of the ostracod. It is also important to find a specimen whose surface has not been etched by micro-organisms since this may have destroyed many of the specimen's features. A selection of possible suitable specimens is made using an optical microscope. This was done in order to eliminate those specimens which were obviously unsuitable for examination. This saved considerable time since, in order to view a specimen in the scanning electron microscope, each specimen has to be prepared before it can be placed in the microscope. 2) Once the suitable specimens have been selected they each have to be mounted on a stub - specimen holder. Different makes of electron microscopes use different types of stubs. In the case of the JEOL range of electron microscopes, the stub is a small, cylindrical piece of brass. Another common type of stub is a small circular disk with a protrusion from its base, typical of the Cambridge range of electron microscopes. Stubs are produced on milling machines and consequently circular milling marks are engraved on the top of the stub. Under high magnification these milling marks are quite noticeable and can distract from the image of the specimen. The first step in the mounting procedure is to attach a small circular disk of black photographic paper onto the top of the stub. The paper is attached with double sided sticky tape. The paper is used to ensure that the background of the specimen is as smooth and unobtrusive as possible. The ostracod is then glued onto the center of the paper. Only-certain types of adhesives are suitable for use in electron microscopes. Certain adhesives, which contain solvents, cannot be used in electron microscopes due to their property to degas, which creates problems when attempting to create a vacuum (Wischnitzer 1970). The glue that was used in this case was a water soluble glue which gives off no vapors at all. 3) Once the ostracod is mounted on the stub, the specimen needs to be coated with a conducting material. This ensures that the specimen is conductive even though ostracods themselves do not conduct electricity well. It was mentioned in a previous chapter that a specimen in the microscope is continually exposed to an electron beam. The image that is formed is a measure of the variation in the intensity of the secondary electrons collected from the specimen. Consequently, if charging of the specimen occurs, it results in the specimen having a varying electrical charge. This distorts the intensity of the secondary electrons and a distorted image is formed. If a specimen is a conductor, its charge can be led off it onto the stage and charging will not occur. The potential of the specimen will be maintained at a constant level. If non-conducting specimens are coated in a conducting material the same effect can be achieved (Wischnitzer 1970). It is difficult to ensure that all parts of the ostracod are coated (ie underneath overhangs). If the coating does not entirely cover the surface of the ostracod, the specimen may still become charged on occasions. There are various materials used for coating specimens, including gold, gold-palladium and palladium. Gold, which was used to coat the ostracods, is one of the most common coating materials. In order to coat the ostracod, it is placed in a specimen coating machine for approximately 5 minutes. The machine that was used was a BIO-RAD E5100 sputter coater made by Micro Science Division shown in Fig.1.7. 14 / 65

Fig. 1.7. The BIO-RAD E5100 There are various different methods to coat specimens; sputter coating is one such method. The stub is placed in the machine and rotary pumps create a vacuum. Argon, which is an inert gas, is then pumped through the specimen chamber to remove any particulate impurities and residual moisture from the chamber and the specimen. A very high current of electricity is then passed through a gold disk. The extremely high current causes the gold disk to heat up. This allows some of the surface molecules of the disk to vaporize and form a plasma. The continual stream of Argon flushes the gold molecules towards the stub and a fine layer of gold molecules is deposited on the surface of the ostracods. The layer of molecules is between 0.01 µm and 0.1 µm thick (Wischnitzer 1970). It is important to realize that the gold does not adhere to the specimen, it merely settles on it. For this reason, it is very important not to touch the specimen once it has been coated, otherwise the coating will come off. Only the stub should be handled and then only with a pair of tweezers. As much care as possible should be taken to ensure that dust does not collect on the stub once it has been coated. Any dust which lands on the stub will obviously not have been coated in gold and since dust is not a conductor, it may cause charging which will result in a degraded image. 4) The operation of the microscope, its vacuum pumps, and its cooling system is automated and controlled by software. The user merely has to push a button on the control panel (Figure 8) and the software automatically ensures that the necessary operations are carried out in the correct order. The software continuously monitors the microscope and alerts the user to any faults or malfunctions. The stub with the coated ostracod is placed in the microscope column on the specimen stage shown in Fig. 1.8. The operator closes the door to the chamber and instructs the microscope to evacuate the chamber. The chamber is evacuated to an approximately 35 percent vacuum using an mechanical rotary pump. Once a 35 percent vacuum has been reached it becomes impractical to continue to use a mechanical pump. Any further evacuation would be time consuming and restricted by the mechanical limitations of the pump. The software now switches to a non-mechanical, oil diffusion pump completes the evacuation of the chamber to form a 99% vacuum.the oil 15 / 65

diffusion pump is far quicker and more effective than a rotary pump. The rotary pump evacuates at a rate of only 100 1/min whilst the diffusion pump evacuates at a rate of 420 1/sec. The whole evacuation process takes only about 3 minutes. Fig. 1.8. The electron microscope column 5) The desired strength of the electron beam is now entered into the microscope software. Although the strength was set at 20kv for these micrographs, it can be set between 1 kv and 25kv (7 steps). A high electron beam strength gives a better resolution of the displayed image than a low strength. However, high strengths are more prone to cause charging than low strengths and also reduce the lifespan of the electron-gun filament. The ostracod is moved into the centre of the screen using x-axis and y-axis verniers to move the stage in the x,y plane. The specimen can be moved 10mm in the x direction and 20 mm in the y direction. The specimen can also be rotated. The magnification is set to the desired level, in this case 500x. The contrast and focus are then adjusted until a clear picture of the ostracod on the Cathode Ray Tube (CRT) is obtained as in Fig. 1.8. Once the desired image is obtained, a picture of the screen is taken. The camera, which is attached to the microscope by a hinge, is swung into place over the screen. The camera, through its link to the microscope's software, is then instructed to take a picture of the screen. If the intention is to take stereo photographs, the specimen needs to be tilted before a second photograph is taken. If the specimen is being viewed under high magnification, it may move off the screen once it has been tilted. It will be necessary to readjust the specimens position with x or y movements to reposition it on the screen. 1.6.2. The affect of stage tilt on the stereo effect of micrographs We are used to viewing objects in daily life in stereo. This stereoscopic effect occurs because we are able to view objects with two eyes. There is a line of sight from each eye to the viewed object. Since our eyes are separated by a certain distance, the two lines of sight must converge on the object. The intersection of the lines of sight forms an angle. This angle is a function of the distance between 16 / 65

the eyes and the distance to the object. The closer an object is to a person, the greater the angle between the lines of sight. Conversely, the angle between the lines of sight to an object far away is very small. The distance between each person's eyes is constant. Any variation in intersection angle to different points is therefore caused by a variation in the distance to those points. Our brain, through its efforts to focus the eye, compares the intersection angle at one point to another. The point which produces the greatest intersection angle is the point closest to the person. In this way we are able to perceive depth. If an object is viewed with only one eye, the stereoscopic effect will not occur and the viewer will not be able to perceive depth. However, we can perceive depth using only one eye by other means. Amongst others, these include interpretation of shadows and knowledge of the relative size of the objects with respect to each other. A photograph has the same effect as viewing an object with only one eye. A single photograph gives no stereoscopic effect; there is no sensation of depth. However, it is possible to produce a stereoscopic effect if two photographs of an object are taken from slightly different positions. The two photographs are known as a stereo pair. By viewing each photograph with a separate eye, a stereoscopic effect can be created, as in Fig. 1.9. This has the same effect as viewing an object with two eyes since each eye sees a different image. What is seen is a stereo model; an imaginary replica of the object. Fig. 1.9. This diagram shows how a stereo pair can create a sensation of depth. Although the stereoscopic effect can be recreated without an instrument, it is more convenient to use one since this allows the image to be magnified. A slightly different procedure has to be followed when attempting to form a micrograph stereo pair. In terrestrial photogrammetry it is usual to move the camera around the object. In an electron microscope, the electron probe is the effective position of the camera. It is impossible to move the electron probe around the specimen, instead, the specimen must be tilted. Tilting the specimen creates an effective spatial separation between images. The tilt 17 / 65

angle is the angle of intersection between the lines of sight to the specimen from the two different effective camera positions. The amount by which the specimen is rotated affects the quality of the stereoscopic effect. The nature of the specimen and the magnification used, influence which tilt angle is likely to be the most suitable. Specimens with little relief require a large exaggeration of the relief in order to distinguish height differences between points. Specimens with a great relief require only a small exaggeration of relief. If the relief were too exaggerated, it would be difficult to interpret from the stereo model. In theory, a tilt angle of 90 would provide the maximum stereoscopic effect. However, very large angles cause surface features to obscure each another, creating stereoscopic gaps (Ghosh 1989). If a very small intersection angle is chosen, it is difficult to perceive depth; a small angle has the same effect as viewing an object from a distance. Ghosh and El Ghazali (1977) reported that an angle between 8 and 20 would give adequate results. They reported that an angle between 10 and 15 degrees was usually the optimum angle (Ghosh 1989). If a specimen has very little relief, a relatively large intersection angle will emphasize differences in depth. A smaller angle is needed for specimens with considerable relief to ensure that tilting does not obscure too much of the specimen surface. Researchers at the South African Museum use stereo micrographs of ostracods purely for interpretive purposes. They do not take measurements from the micrograph. The researchers have always used a tilt angle of 5. Since this angle appears suitable for their purposes, they have not experimented with other angles. It has been chosen to study different scenarios in order to determine: 1) whether a tilt angle of 5 was the most appropriate for their specimens. 2) whether a change in magnification of their specimens would require a different tilt angle. Two specimens were used; an ostracod and a groove scratched into the top of a stub. The same part of the ostracod was viewed at two different magnifications; 200x and 500x. Micrographs of the groove (at 500x) were made in order to determine whether the optimum angle was any different to that of the ostracod at 500x. The groove is approximately 225 µm wide. Around the edge of the groove is material which has been pushed up from inside the groove. The background is flat. Micrographs of each of the three cases were made at 5 intervals starting at 0. The micrographs were viewed through a Sokkisha MS-2 7 mirror stereoscope with 3x magnification. They were evaluated in pairs; the 0 tilt micrograph and a micrograph with another tilt angle. The micrographs were evaluated for ease of interpretation. This is a subjective procedure and the angle which was determined as being most suitable may not be the best for all people. 1.7. REMARKS ON TILT ANGLES Although this is a subjective experiment, it does illustrate the benefit of investigating a few different tilts for each specimen or magnification. The ideal combination for interpretation can then be selected. However, it may not be viable (either financially or for other reasons) to photograph a number of tilts for each specimen. If this is the case, then this investigation indicates that a tilt between 20 and 25 is likely to produce the most useful images. This differs from Ghosh's recommendations that an ideal tilt for most specimens lies between 10 and 15 (Ghosh 1989). However, Ghosh's recommendations are in relation to micrographs from which measurements are to be taken. Furthermore, Ghosh's investigation most likely involved far specimens with greater variation in surface relief than the presented study. 18 / 65

The presented investigation showed that different specimens and magnifications require different tilt angles. However, a tilt angle of 20 would have been adequate, although not necessarily ideal, in all three examples. This investigation does indicate that the researchers at the South African Museum could benefit by using a tilt angle of at least 20 instead of 5 which is currently used. A tilt angle of only 5 does not fully take advantage of the benefits of stereo electron micrographs vision. 1.8. DISTORSIONS WHICH AFFECT A MICROGRAPH IMAGE It was mentioned previously that it was possible to measure the spatial coordinates of points on the object directly from the micrograph. This assumes that the micrograph image is free from any distortions. Unfortunately, this is not the case. If the user wishes to obtain the most accurate measurements possible, he must take into account distortions which occurred when forming the micrograph image. Corrections for these distortions must be applied to the micrograph coordinates before the model coordinates are calculated. There are two stages during which distortions in the production of the micrograph can occur: externally once the photograph has been taken; and within the microscope during the formation of the image. Distortions external to the microscope are such distortions which are encountered whenever photographs are taken. Since they are not unique to electron micrographs, they will not be elaborated upon. However, the reader should be aware that the usual photographic distortions also apply when forming micrographs. These distortions may be caused by the lens of the camera or by the film not being flat during exposure. Distortions can also be introduced during development of the film. Some distortion may occur when producing a positive print from a negative. Since photographic paper is much less stable than film, it is advisable to take measurements from negatives rather than from positive prints or use the digital image from CCD photographic camera. Distortions caused by the microscope are caused by the nature of the electron beam and fall into two categories. Firstly, certain distortions can be corrected for within the microscope by using special lenses and other equipment. The effects of these distortions are largely removed before the image is formed. They have little effect on the final micrograph image if the microscope is functioning properly. They will not be discussed in this chapter since most microscopes attempt to correct for these distortions. However, there is a second category of distortions whose influence cannot easily be corrected for within the microscope. These can influence the final micrograph image. Corrections need to be applied to the micrograph coordinates of each point measured on the micrograph to correct for these distortions. A correction should be applied for each type of distortion. In the following section the various distortions will be presented. 1.8.1. Perspective distortion An electron micrograph system is best represented by a perspective projection. However, as mentioned in the previous chapter, a parallel projection can be assumed for the sake of convenience. By assuming a parallel projection, perspective distortion is introduced. The coordinates of each point measured on the micrograph must be corrected for the difference between parallel and perspective projections. 1.8.2. Scale distortion This distortion occurs as a result of the method scanning electron microscopes use to magnify an image. A scanning electron microscope magnifies a portion of an image by amplifying the secondary electrons which it collects from that portion of the specimen. 19 / 65

Theoretically, the magnification is equal in both x and y directions (and it is the magnification entered by the user). However, in reality it is unlikely that this is the case. Scale affinity is likely to occur; there is a difference in the x and y magnifications. This causes a distortion which can be corrected if the calibration data of the particular electron microscope being used is known. The correction can be included in the stereo model for the parallel projection. This is done by replacing the magnification M, with M x and M y. Fig. 1.10. The scale distortion Figure 1.10 above gives a graphical impression of how scale distortion will affect an image. The original image consisted of a square grid which was converted to rectangular grid. 1.8.3. Radial distortion Radial distortion is similar to that encountered in conventional photogrammetry. The distortion may be either positive (outward from the principal point) or negative (inwards towards the principal point). Fig. 1.11. The positive radial distortion outward from the principal point of the micrograph. 20 / 65

Fig. 1.12. The negative radial distortion inwards from the principal point of the micrograph. The radial distortion may be expressed as a polynomial. 1.8.4. Spiral distortion In an earlier section dealing with magnetic lenses, it was mentioned that the electrons within an electron beam do not travel in a straight line, instead they spiral. This causes the whole electron beam to twist, which results in an image which is also twisted about the center of the electron beam. Fig.1.13. The S x spiral distortion. 21 / 65

The center of the electron beam is the principle point of the image: it is the only point unaffected by spiral distortion. The effect of spiral distortion on a particular point is a function of the radial distance of that point from the principle point of the image. Fig.1.14. The S y spiral distortion. The radial distance has components in both x and y directions. Since there is the possibility of affinity (different scale in x and y direction), the distortion in x and y directions may be different. The effect of the two spiral distortions can be seen in Figures 1.13 and 1.14. 1.8.5. Image rotation. This phenomenon occurs when the entire image appears to rotate when the magnification is varied. The effect is that the image changes orientation for each increase in magnification. It is caused by the rotation of the electron beam. However, this is not due to the same natural effects of magnetic lenses as spiral distortion was, rather, for amongst other reasons, to imperfections in the alignment of lenses, variations in current and changes of projection distances (Ghosh and Adiquzel 1984). They state that the correlation between magnification and rotation is systematic. They also state that image rotation in a scanning electron microscope can be considered to be negligible for most applications. It can be completely ignored if the magnification for all related micrographs is kept constant. Although image rotation can largely be ignored for scanning electron microscopes, it has been included in this chapter to draw attention to its role in transmission electron microscopes. Whilst much of the geometry, coordinate systems and distortions apply equally to both types of microscopes, image rotation cannot be ignored in considering micrographs produced in transmission electron microscopes. See Ghosh and Adiquzel (1984) for further information relating to transmission electron microscopes. 1.8.6. Tangential distortion. This distortion was modeled by Maune (1973). It was subsequently found by Nagaraja (1974) that the distortion was effectively compensated for by the correction for spiral distortion (Ghosh 1989). 22 / 65

1.9. IMPORTANCE OF MICROSCOPE CALIBRATION. Various studies have shown the importance of applying corrections to micrograph coordinates to offset the effect of distortions. This leads to an increase in the accuracy of points coordinates which can be determined. Florek (1977) states that an increase in accuracy of at least 100% can gained by applying all possible corrections for distortions. The most influential distortion, and thus the correction which accounts for the greatest increase in accuracy, is scale distortion. The importance of scale distortion can be seen in an example from Ghosh (1980). 1) When uncorrected for any distortion error a=300 nm. 2) When corrected only for scale affinity a=110 nm. 3) When corrected for all distortions a=23 nm. This example also shows the great increase in accuracy that can be obtained by applying corrections for all the distortions. In order to apply these corrections, calibration data of the particular electron microscope being used must be available. The microscope is calibrated by viewing a square grid under high magnification. The grid is made from a master diffraction grating with 2160 lines per millimeter (El Ghazali 1984b). The line frequencies are guaranteed by the manufacturer to be within 1 percent of the given value. The coordinates of the intersection of each line on the grid can be calculated from the information provided by the manufacturer. Micrographs of the grid are formed with various tilts and rotations. The micrographs are measured with a measuring device whose accuracy is known. Any departure of the calculated coordinates from the known coordinates represents evidence of distortion. By measuring a number of micrographs taken from different perspective centers, the calibration unknowns of the various distortions can be found (Ghosh 1989). The accuracy with which the microscope can be calibrated is reliant upon the accuracy of the instrument used to measure the micrographs. It is also dependent on degree to which distortions are introduced when developing the micrograph. Ideally, these accuracies should be known beforehand, so that microscope distortions are not incorrectly assumed to have occurred. 1.10. FINAL CONCLUSIONS 1) It is important that photogrammetrists develop a relationship and dialogue between themselves and the end-user of the results. In almost all cases the end-user is the provider of the stereo images. The photogrammetrist must realize that the accuracy of this results is influenced largely by circumstances beyond his control and that the real accuracy of his results is likely to be far lower than his calculations may imply. 2) However, it is possible that lower accuracies may be quite sufficient for the end users needs. For his part, the end-user must appreciate that they contribute substantially to the final accuracy of the results. In only a few circumstances may it be necessary to calibrate the SEM. For the most part it may be sufficient to explain to the end-user the precautions which they need to take in obtaining the images. 3) In many instances it is not necessary for the photogrammetrist to strive for the greatest possible accuracy in his measurements. Without dialogue between the photogrammetrist and the end-user there may be times when the accuracy of the photogrammetrist's results is meaningless. 23 / 65

4) Various studies have shown the importance of applying corrections to micrograph coordinates to offset the effect of distortions. This leads to an increase in the accuracy of points coordinates which can be determined. REFERENCES AND SELECTED BIBLIOGRAPHY Boyde, A., Ross H.F., 1975. Photogramme-try and the Scanning Electron Microscope. Photogrammetric Record, 8 (46), pp.408-457. Elghazali, M.S., 1984a. Micro-range Appli-cations Using SEM & TEM Micrographs. Archives of ISPRS Congress Commission V, pp.248-257. Elghazali, M.S., 1984b. System Calibration of Scanning Electron Microscopes. Archi-ves of ISPRS Congress Commission V, pp.258-266. Florek, R., Pluta, B., Sokolowski, J., 1977. A Conception of the Stereophotogrammetric Analysis of the Surface being Abraded on the Base of Scanning Electron Micrographs. (in Polish), Biuletyn IGiK, Warsaw, Poland, 5, pp.62-64. Ghosh, S.K., 1975. Photogrammetric Cali-bration of a Scanning Electron Microscope. Photogrammetria, 31; pp.91-114. Ghosh, S.K., Nagaraja, H., 1976. Scanning Electron Micrography and Photogrammetry, Photogrammetric Engineering and Remote Sensing, 42, (5), pp.649-657. Ghosh, S.K. et al, 1978. Three Dimensional Mapping by Combining Transmission and Scanning Electron Microscopes. Paper pre-sented at the ISPRS Commission V Sympo-sium, Stockholm, Sweden, 10pp. Ghosh, S.K., 1980. Future Possibilities of Precision Mapping with Electron Micro-scopy. Invited Paper to XIV Congress of ISPRS, Commission V, pp.244-251. Ghosh, S.K., 1989. Electron Microscopy: Systems and Applications. Non-Topogra-phic Photogrammetry. ASPRS, second edi-tion, pp.187-201. Kordylewski, L., Florek, R., 1990. Stereogrammetric Measurements of Cell Membrane Structures in Freeze- Fracture Replicas. First Regional Meeting of the American Society for Cell Biology. Chicago, p.34. Kordylewski, L., et al, 1994. Atomic Force Microscopy of Freeze Fracture Replicas of Rat Atrial Tissue. Journal of Microscopy. Vol.173, 9 pages. Maune, D.F., 1976. Photogrammetric Self Calibration of Scanning Electron Micro-scope, Photogrammetric Engineering and Remote Sensing, 42 (9); 1161-1172. 24 / 65

2. PHOTOGRAMMETRIC MAPPING OF THE ARCHEOLOGICAL SITE WITH THE USE OF AIR-PHOTOGRAPHS AND DIGITAL STEREO RESTITUTORS The work described in this chapter arises from a joint project between the Departments of Surveying and Geodetic Engineering, and Archaeology conducted by Dr. Florek. Following an approach by the Archaeology Department to map a suspected archaeological site, the Department of Survey decided to use this request as a case study in the comparative analysis of aerial and terrestrial photography in the recording of sites for mapping purposes. It was further decided to use this study for a comparative evaluation of analytical and digital photogrammetric processes in the interpretation of an archaeological site. 2.1. INTRODUCTION Both an aerial and a terrestrial survey were planned and undertaken. The positions of the control points for the terrestrial survey were determined during a reconnaissance of the site. A view finder was used to estimate the number of photographs needed to cover the site. The photo base positions were arranged in such a manner that the important details of the site would be recorded. The photographs were taken in a manner which enabled stereo models to be produced. These models were used in the interpretation process. Two main problems were encountered. The first of these was caused by poor planning and resulted in the western side of the site having too few control points. This necessitated the taking of very oblique photographs. The second problem was that the cameras were not perpendicular to the photo base. This disallowed the use of some of the stereo pairs for the production of 3D models. An aerial survey was undertaken, because the flight was sponsored by Court Helicopters. The preplanning of this survey involved the determination of the number of photographs to be taken, the height of the flight, the flight lines and control point positions. It was determined that the helicopter should fly at a height of 320 m, to enable four photographs to be taken for complete coverage of the site with one flight line. A flight plan was compiled and showed the photograph overlapping section of each photograph. This plan was then used to determine the positions of the aerial control points which were to be located at the corners of each model. The final map was produced from these photographs. This project was not without mishaps as the left photograph of the second model was taken too late. Three of the six control points did not appear on the photograph, so could not be incorporated in the model. This problem was overcome by the use of terrestrial control points. Two cameras were used in both surveys. They were MAMIYA professional non-metric cameras. They had a principle distance of 80mm and they produced 6 by 6 cm negatives. The results obtained were lower than the a priori calculated values. This was, however, expected as the a priori calculations did not take into account the inherent inaccuracies of the ground co-ordinates and targets. Although the results were lower that the a priori values, only the Y RMS error in the first model exceeded the minimum accuracy allowed, but only deviated by 4cm. The results gained from the photographs varied with the three models. The first model gave the lowest accuracies, which could not be accurately explained. These accuracies were gained from the Adam Topocart stereo restitutor. The negatives which made up the first stereo model were scanned and interpreted on the DVP (Digital Video Plotter) software. Unfortunately, due to financial constraints, only two negatives could be scanned. The results that were obtained were expected to be less than those gained from the Topocart as resolution and accuracy would be lost during the scanning of the negatives and the output of the images on the computer screen. The results gained from the interpretation of the images were as expected with the X and Y RMS errors being 10-20 percent less accurate. An unexpected finding was the halving of the Z RMS error when compared to the X and Y errors. While the exact reason for this 25 / 65

is not known, several possibilities were discussed. This study suggests that the choice of photographic survey should be determined by taking into account the properties of the site. These properties would include the size and relief of the site terrain. This report is a result of a combined project between the Department of Surveying and Geodetic Engineering and the Department of Archaeology of University of Cape Town. The Archaeology Department approached Dr. Florek from the Survey Department requesting him to produce a map of an archaeological site. The Survey Department decided to use this archaeological site as a case study in order to investigate the advantages and disadvantages of the Archaeology Department using aerial or terrestrial photography with respect to the recording of smaller archaeological projects undertaken by them. A further investigation was done for the Survey Department into the results achieved from analytical and digital processes. An aerial and a terrestrial surveys were planned and undertaken. Both photographic surveys required control points where the X, Y and Z co-ordinates were known. The conventional survey was used to place both the terrestrial and aerial photographic control points. Aerial photographs were taken from a helicopter, the flight being sponsored by Court Helicopters. The processing of the aerial photographs was done on the Adam Topocart stereo-restitutor and the contour map produced on the Sun workstation. The contours were computer drawn. The aerial photographs included three stereo models, the photographs that constitute the first model were sent to a firm in Cape Town to be scanned and put into digital format. These images were then put onto the department computer and Leica DVP station was used to process the images. A major constraint was the helicopter flight, in that it was a sponsored flight. The flight could only be undertaken when the helicopter company was ready to fulfill their sponsorship. Other constraints that related to the DVP station were, that the station was used for the first time in the Survey Department for a such project using aerial and terrestrial photos simultaneously. 2.1.1. Glossary of terms Coverage - A set of thematically associated data considered to be a unit. A coverage usually represents a single theme or layer, such as soils, streams, roads and land use (Glossary of Photogrammetry, GIS and ARC/INFO terms) Steenbok - Small antelope Flight plan - A plan that indicates the path along which the plane must fly, it also indicates as to when the photographs are to be taken Fynbos - Type of vegetation indigenous to the area of Western Cape in RSA Lattice - A surface representation that uses a rectangular array of points spaced at a constant sampling interval in the X and Y directions relative to a common origin (Understanding GIS, The ARC/INFO method) Macro - A macro allows you to automate frequently performed actions, create your own commands, provide startup utilities to help new or inexperienced users perform operations that require specific command settings, and to develope menu-driven user interfaces to meet the needs of end users Stereo restitutor - An instrument used for the reconstruction of the 3D model and the acquisition of 3D data by stereo digitising Tin - Triangular irregular network View finder - Component of a photographic camera showing the extent of image seen on a photograph 26 / 65

Fig. 2.1. The archeological site area between red lines. 27 / 65

2.1.2. History of the site On the 22 December 1646, the Haerlem set sail from Batavia, Holland in the company of 2 other ships, the Olifant and the Schiedam. The ships arrived in Table Bay on Western Cape South African coast on the 22 March 1647. The Haerlem, after being caught in an unpredictable wind, ran aground on 25 March 1647 and was latter wrecked by the force of the waves. Provisions were taken from the ship with the help of the sailors from the other 2 ships. Some of the provisions and about 40 men where accommodated on 2 English ships that had anchored in the Bay, and taken to St. Helena. An extra 40 men returned to Holland on the Olifant. This meant that about 60 men along with Chief Mate Walles (of the Haerlem) were left behind to return to Holland on a later vessel. They spent 6-8 months at the Cape bartering for supplies from the "Strandloopers". The records from the crew of the Haerlem were of great use to Jan van Riebeeck when he landed at the Cape. The crew of the Haerlem fostered good relations with the Strandloopers, and this enabled good bartering between van Riebeeck and the Hottentots. Jan van Riebeeck also wrote in his diary that one of the "savages" could speak a little English. 2.1.3. Description of the archaeological site The site is situated on the beach alongside Rietvlei shown oin Fig. 2.1. for an extract from a 1:10 000 orthophoto map). It is an area approximately 150 m wide and 300 m long and is situated between the beach and Otto Du Plessis road R27. The site was found by an archaeologist using maps drawn by the sailors and stored in the Dutch Government archives. These maps relate the site to the position of Robbin Island and the Castle shown in Fig. 2.2 source: Algemeen Rijks Archiest, The Hague Netherlands Eerste Afdeling, Collection Leupe No 178, 50/72 manuscript note. The dark "bumpy" border surrounding the diagram represents the mountains seen from the site. The site is found in the dunes and consists of a natural depression of about 80 by 20 m in size. This hollow is situated between the two highest dunes in the area, this provided an excellent vantage point for the sailors. The site is bordered by the sea on one side and Rietvlei on the other. This meant that only 2 approach route were available. Because the hollow is surrounded by dunes, it is protected from the south easterly and north westerly winds. Access to the site is from the road R27 and it appears that it is frequented by the general public. The predominant flora is Cape beach fynbos and a few steenbok have been seen on it. The site is in danger of being demolished in preparation for a housing development. If it is confirmed to be of archaeological importance, it will be declared a national monument and will be preserved. 2.1.4. Literature review of papers on photogrammetric documenting of archaeological sites. Photogrammetry has been used extensively in the recording and analyzing of archaeological sites. This is predominantly for two reasons. Firstly, that the taking of photographs provides a cheap, long lasting record and can be used compare the progress made on an archaeological site. Secondly, it provides a way for the quick recording of objects, this is important for sites that are only visible for a short period of time. Aerial photography has been used to record larger sites, however, due to political or financial reasons, researchers have been creative in the photographic platforms they have employed to take their photographs. The platforms include kites (Anderson, R.C), balloons (Wanzke, H) and radio controlled helicopters and airplanes. Aerial photography provides a better coverage of the site, if the site is on very uneven terrain. This was the case with the archaeological site used in this study. 28 / 65

Fig.2.2. Map drawn in Jan van Riebeecks time indicating the position of the Haerlem wreck 29 / 65

Surveying and photogrammetric documenting of monuments and archaeological sites was regulated in many countries. The technical standards were elaborated in Poland and similar were produced in other countries (1981, Butowtt R, Florek R, Sitek Z, et al). 2.2. TERRESTRIAL PHOTOS WITH RESPECT TO ARCHAEOLOGY This topic is being treated separately here in that the choice of metric or nonmetric cameras can affect the accuracy obtained for the survey. Metric cameras have been designed for the purpose of gaining accurate measurements from the images taken. Lenses are free of distortion and also include the calibration data. This data provides the principle distance, to the accuracy of 0.01 mm, and elements of the radial distortion of the lens. The camera also contains fiducial marks or a reference (reseau) grid. These are either placed in the midpoint of the edges of the photograph or in the corners of the photograph. Some cameras contain both types of fiducial marks. Metric cameras can be used with cut film or glass plate. The latter provide greater accuracy, as the film distortion is greatly reduced due to a thicker base. Glass is also more stable than film. A disadvantage of these cameras however, is that they are generally very heavy and expensive. This can be minimized though, as small metric cameras are available (eg. Rolleiflex camera). Any camera that does not include the above mentioned elements is regarded as a non-metric camera. The lenses of nonmetric camera are not produced to the same precision and the recorded image is thus often distorted by the lens. It is also necessary to note that some non-metric cameras have better lenses than others. Then it necessary to calibrate non-metric cameras for estimation of interior orientation elements. The cameras used in this survey were two MAMIYA non-metric cameras and were chosen because they had good lenses. They could also be adapted to use a cut film. Both cameras had been calibrated for short range photogrammetry and this data was available (Adams, L.P). Film used by these cameras is readily available in both black & white and color slide format. The planning phase of a survey is of utmost importance as time, effort and money can be lost due to poor planning. It is important to undertake a thorough reconnaissance of the site to determine the position of control points and number of photographs needed. It is necessary to do this using some sort of view finder which is compatible with the camera which is to be used. A problem experienced with the terrestrial photographs was the lack of sufficient control points on the western side of the site. This gave only the minimum number of control points per stereo pair. This error was a direct result of bad planning. A good stereo model needs a minimum of 4 control points per stereo pair with 2 being in front and 2 at the back of the model. The position of the control points should be determined at the planning stage. The terrestrial photography performed required a large number of control points which took two days to place. A traverse between two town survey marks was used to bring the control into the area and to tie them to the national system. This was requested by the archaeologist. X, Y and Z values were determined for each control point. They were placed in prominent positions, but were hidden from the public eye. This limited the likelihood of a member of the public removing them. A plan showing the distribution of control points is given on a map shown in figures 2.3 part top and 2.4 part bottom B. Photogrammetric technology requires so called control points which should be clearly marked on the ground as specially designed targets. Targets should be constructed in such a manner that they are clearly visible on the photographs. This is largely dependent on the pattern chosen and photo scale. One of the most commonly used patterns is that shown in Figure 2.5. It is important that the center of the target be clearly visible. Targets should have a minimum size of 0.2 mm on a photo which is a size of stereo restitutor floating mark. The formula for the calculation of target size t s is: t s = a c b Where a=0,2 mm; b=principal distance; c=average distance of target from photo base. 30 / 65

Fig.2.3. Map showing wreck site place and distribution of control points part A, top of the map. 31 / 65

Fig.2.4. Map showing wreck site place and distribution of control points part B, bottom of the map. 32 / 65

Fig.2.5. The most commonly used patterns with the center of the target clearly visible. Targets size should be minimized as they can obscure some detail behind them. If the control points are situated close to the ground, it might be necessary to construct a device which would make it possible to locate them on the photograph. In the photographic survey undertaken, targets were placed on ranging rods and placed directly behind the points. Although this is not an accurate method, it complied with the accuracies of the project, in that the project was for topographical purposes. Two sets of targets were used with the first being one that could clearly be seen and would indicate the position of the control point. This particular target is shown in Figure 2.5. A second set of targets was used to identify the names of the control points. This set had six different patterns which are shown in Figure 2.6. These targets do not represent the best shapes or patterns, as they were not used for accuracy purposes, but for recognizing control point names. Two targets were attached to each ranging rod, with the positioning target being 0.68m above the ground while the point recognizing target was placed 1.18 m above the ground. The height of the targets was recorded and added to the height of the control point. There were six targets in each set, 4 targets were 15 x 15 cm in size, the remaining 2 were 20 x 20 cm in size. Control points that were more than 80 m from the camera base were identified by the larger sized targets. The types of film used were the following. Stereo pairs were taken on black & white film, while color slides were taken with each stereo pair to aid in the interpretation of the stereo model. For the center of the site, color slides were used to take stereo pairs. This was done to provide a second set of photographs as a backup. The black & white film was preferred as it was cheaper than the color slide and the developing could be done in the Department by the author. The following procedure of taking photographs was applied. The orientations of the 2 photographs which make up the stereo model are important. It is recommended that the cameras be perpendicular to the photo base. The size of the photo base determines the depth of field of the stereo model. A chosen photo base (PB) distance will result in a depth of field (DOF): 4 PB < DOF < 20 PB Where 4*PB is used as a limit due to stereovision limitations and 20*PB is used because of required accuracy. 33 / 65

Fig.2.6. The set of targets which was used to identify the names of the control points. This depth of field equation can be used in another manner and that would be to estimate how close the camera should be from the closest recorded object. By this is meant that if a depth of field for eg. 8 m to 40 m is calculated, then the camera should not be closer than 8 m to the object that is being recorded. Benefits and shortcomings of using terrestrial photographs are that terrestrial photographs are beneficial in recording data on steep slopes and vertical walls. This method is cheap as the only equipment that is required is a tripod, camera and the film. This minimum of equipment means that it is very portable and can be used to take photographs of sites or artifacts that are only visible for a short time. This method has a large shortcoming in that it cannot be used to record the depth of a dig. This is demonstrated in Figure 2.7. Samples of 4 terrestrial photos are shown in Fig. 2.8. presenting wreck site. 34 / 65

Fig. 2.7. Difficulties to record depth of dig. Fig. 2.8. Some of the terrestrial photos. 35 / 65

2.3. AERIAL PHOTOS WITH RESPECT TO ARCHAEOLOGY This form of photographic survey is definitely the easier of the two, as it requires less photographs. However, it can be more expensive depending on what sort of platform is used. A platform is a piece of equipment to which cameras are attached in order to take the photographs. Any piece of equipment that can hoist a camera can be used as a platform. The literature describes a number of cheap aerial photographic platforms. Two that the author would like to highlight are those of the balloon and kite. Both these platforms have been used to document archaeological sites. They are very useful in cases where the use of a helicopter or planes is not allowed either due to financial or political reasons. Recently, the drones or rather UAV - Unmanned Aerial Vehicles have gained wide practical popularity. The author has not experimented with these platforms, so a discussion of these platforms shall be left to the relevant papers. The platform used to undertake this survey was a helicopter. A special piece of equipment needed to be constructed in order to hang the cameras under the fuselage free from the possible interference of the helicopters landing gear. Photograph 2.9 shows the helicopter and the landing skids. Fig. 2.9. The helicopter and the landing skids. 36 / 65

Photographs in Fig. 2.10 show the camera mounting used to take the photographs. It was very simple but practically useful to carry two photographic cameras. Fig. 2.10. The camera mounting used to take the photographs. A bubble was placed on the camera mounting in order to eliminate tilt as shown in Fig. 2.11. The camera was operated by two people with the first person holding the camera mounting in a vertical position and taking the photograph. The second person used the bubble to level the mounting apparatus. Fig. 2.11. A bubble was placed on the camera mounting in order to eliminate tilt. 37 / 65

2.3.1. Flight planning The planning for aerial photography needs to be done carefully, because an aerial photographic survey involving an aircraft is very costly. The first aspect to consider when planning the survey, is that of the scale of the final product. There is a general rule that is applied, which says that the final product should not be greater than a 10 times enlargement of the negative (Florek R.) Although this rule is very general, it lays down a guide-line as to the scale of the negative. If the scale of the negative is too small, detail could be lost in the photograph and this would decrease the accuracy obtained from the model. Once the scale has been determined, the number of strips and photographs per strip can be calculated. For the survey undertaken, it was decided that a 1:400 map was desired as a final product. Therefore, this determined that the scale of the negative should not exceed 1:4000. When the negative scale is chosen, the area recorded on a negative can be calculated. A simple formula is then used to calculate the flight height. See Figure 2.12 for the equation. Fig. 2.12. The area recorded on a negative. Once all this data has been assimilated, it can be used to calculate the number of flight strips needed. For the aerial survey undertaken, one strip was required with 4 photographs. Once this has all been calculated, it is then necessary to calculate the cost of such a survey, if this falls within the limits of the budget, then the flight plan can be accepted, if not, then the process should be repeated till a suitable solution is found. The flight plan calculated for the aerial survey is shown in Figure 2.13. The next step is to plan the control points distribution. Once the final flight plan has been compiled, it is then used to determine the placement positions of the control points. The minimum requirements needed in order to resolve the unknowns are 2 X, Y and 3 Z co-ordinates. Therefore, a minimum of 3 control points is needed per stereo pair. From a photogram metric requirement, it is preferable to have a minimum of 3 X, Y and 4 Z control points per model as the redundancies can be used to determine a better least squares solution. A control point should be situated in each corner of the model. This ensures that the parallax at the corner of the model is eliminated. There also needs to be a control point in the center of the model to resolve the parallax at the center. For an example see Figure 2.13 (flight plan). A brief description of the calculation of the control points for the photographic survey follows. The center of each photograph was calculated while the distances between them were scaled off the flight plan. The flight line was taken to run parallel with and 75 m from the road. The center control points were placed along this line. Two extra control points were calculated, one on each side of the center point. This allowed for the use of the control points in two stereo models. The distance between the photograph centers was 96 m. 38 / 65

Fig. 2.13. The flight plan calculated for the aerial survey 39 / 65

Fig. 2.14. The distribution of control points part A, top of the map. 40 / 65

Fig. 2.15. The distribution of control points part B, bottom of the map 41 / 65

2.3.2. Control points and targets See Figures 2.14 and 2.15 for a plan showing the distribution of control points. The following step was targeting the wreck place area. The choice of target pattern and size, follows the same principles that were discussed in the terrestrial photography section. The targets used in this survey were 60 x 60 cm targets with the pattern shown in Figure 2.5. Twelve of these targets were constructed, one for each control point. The targets had a hole in the center which allowed it to be placed over the control point beacon. Two types of film were used in the survey, black & white and color slide film. The black & white images were interpreted and the spot heights were taken from these images. The color slides were used for the identification of points if the black & white photographs were not clear. Fig. 2.16. The samples of aerial stereo photos. The following benefits and shortcomings of aerial photography occurred. Aerial photographic surveys are not limited to using airplanes or helicopters as platforms. These two platforms are rather expensive to use. There are a number of cheaper airborne platforms that have been successfully used, 42 / 65

these include balloons and kites. Aerial photographs are very useful when the site to be mapped is large. There are however limitations in that the higher one is above the site, the more detail on the ground is lost. Aerial photographs cannot be used to document vertical slopes. An important feature of aerial photography is that photographs can be used as a progress record. These records could be used to reconstruct parts of the site, if this becomes necessary. The samples of aerial stereo photographs taken appear below, in sequence in Fig. 2.16. 2.3.3. Processing of aerial photos Photogrammetric processing of aerial photographs was intended with use of stereo restitutor. This section of the report deals with the accuracies expected and gained from the aerial photographs. The reason being that the aerial photographs were used in the interpretation process on both the analytical and the digital instruments. The accuracies referred to here, are a measure as to what accuracy the height can be gained from the final map. There are two standard equations that are used around the world that state the accuracy to be obtained. The results gained from these equations represent the minimum accuracy allowed in the official production of maps. For the purposes of this report the American equation was used. The minimum accuracy allowed for the project was 0.5 m, this was for a map with contour intervals of l m. The analytical instrument used was the Adam Topocart stereo-restitutor. An analytical instrument uses a computer program to calculate the unknowns in setting up a stereo model. These unknowns are solved for and applied continuously during the use of the model. Fig. 2.17. The Adam Topocart stereo-restitutor. The input of data to the Adam Topocart is organized by analytical system. The name of the stereo pair model is chosen, then data about the photographs is entered onto a number of cards. There are 9 cards, card 1 and 2 are important and must be filled in. Card 1 stores data such as photograph size, principle distance, tip whether it is an aerial or terrestrial photograph. Card 2 stores data such as the 43 / 65

local co-ordinates of the photograph corners as shown in Fig. 2.18, this card also stores the information which determines whether fiducial or photograph corners are used for the interior orientation. Fig. 2. 18 The local co-ordinates of the photograph corners The co-ordinates and names of the control points are entered onto card 4. There is an important consideration to be remembered when entering the co-ordinates, and that is that the co-ordinate axes of the Topocart are Cartesian and thus have a different orientation, which is shown in Fig. 2.19. Fig. 2. 19 The different orientations of the respective axes. The co-ordinate transformation is relatively easy, but essential. Data such as lens distortion parameters can also be entered onto the relevant card, however, this was not done for this study because this data was not available. The negatives were placed emulsion up on the carriages and an interior orientation was done. Interior orientation on the Topocart entails the alignment of the photographs with respect to each other. This was achieved using the corners of the photographs. This was necessary because the Mamiya cameras are non-metric and so do not have fiducial marks. The corners of the photograph were calculated by intersection. This was carried out by selecting a minimum of 2 points on the edge of each side of the negative. It is important that the same point be chosen on both photographs. This is best achieved by placing the measuring mark of the right eyepiece on the edge of the image, the right carriage is then held fast and the measuring mark in the left eyepiece is moved to the same place on the left photograph. This internal orientation is important in 44 / 65

that, it affects the results gained in the absolute exterior orientation, which has been confirmed by investigation and experiment. Following the interior orientation, an exterior orientation was done. Exterior orientation aligns the detail on the photographs with respect to each other. In the Adam Topocart the relative and absolute exterior orientations are calculated together. This produces the stereo model and is carried out by putting the measuring mark of the right eyepiece on a point of the right photograph (usually it is the control points that are selected for this), the right carriage is then held fast and the measuring mark in the left eyepiece put on the same point on the left photograph and the point is digitized. A minimum of 5 points is needed for this. It is also possible to add pass points, these are points that do not have ground coordinates, but are used in the relative exterior orientation. 2.3.4. Digitising of stereo photos and accuracy analysis Points are digitized by placing the measuring mark on the chosen point and then using the height controls to move the measuring mark up and down until the measuring mark is on the ground. The movement of the measuring mark up and down causes it to move above and below the ground in the model. Important features can be named and selected on the model, such as roads, trees, etc. The list of features can be endless, as the operator enters the name of the feature type. The digitized points are stored on file which contains information such as feature, pen and symbol type as well as the X, Y and Z co-ordinates of the point. There are a number of methods for calculating of Root Mean Square (RMS) errors a priori. There are approaches that involve theoretical calculation eg. C-Factor, and there are those which try to estimate a number of factors which affect accuracy. The C-Factor is defined as "the ratio of the highest flight height which will achieve a specified contour accuracy to the desired contour interval." (Manual of Photogrammetry, pp 398). The flight height calculated for the aerial photography in this report was 320 m, but the pilot flew at 1050 feet (as altitude dial in helicopter is in feet) which translates to ± 330 m. Therefore C-Factor = 330 000 mm = 330 mm 1 000 mm. The C-Factor equation produces an accuracy a priori of ± 33 cm. The problem with this approach is that it does not consider errors due to film, camera lens, quality of photograph, etc. For this approach, the photogrammetrist tries to estimate possible errors as well as possible in order to determine the expected accuracy. Factors taken into consideration are: 1) calibration of analytical stereo restitutor 2) distortion of camera lens 3) distortion of film 4) quality of photograph These errors are squared and added up, then square rooted to produce error. These errors are calculated in micrometers (µm). The accuracy of the Topocart is about ± 5µm known from calibration of the Topocart. The value of the lens distortion is ± about 40 µm (Adams L P). The film distortion is taken as ± 30 µ//m according to own experience (Florek R)). The error as a result of quality of film is estimated to be at ± 20 µm. So estimated accuracy = sqr (5 2 + 40 2 + 30 2 + 20 2 ) = 54 µm. When related to the negative scale of ± 1:4000 this translates to a ± 0,216 m RMS error. It is expected that the individual errors for the X and Y co-ordinates will be similar with the Z co-ordinate being slightly less accurate. Two forms of exterior orientation were performed with the first being relative exterior orientation and the second, absolute exterior orientation. 45 / 65

Relative orientation requires no co-ordinates, it is done to determine whether there was anything drastically wrong with the model. These errors could result from distortion in the film, a weak stereoscopic model with respect to the tilt and rotation angles omega, phi and kappa. This was important as the camera mounting was hand held and the cameras were assumed to be in a vertical position. Tilt angle errors were very possible as the photographs were taken out of a moving helicopter, which meant that the mounting had to be manually compensated for wind resistance. The relative orientation results for the three models were good, taking into account the difficulty experienced in holding the camera mounting. All the rotation angels of the three models were less than 3 degrees. This also showed that there was very little distortion of the negatives. Referring to absolute exterior orientation it requires co-ordinate of the points on the ground. Points without co-ordinate can, however, be used, and are known as pass points. The minimum requirements for this orientation are two X, Y co-ordinates and three Z co-ordinates. However, for an effective least squares solution, sufficient redundancies are required. It is thus recommended that a minimum of 4 X, Y and Z co-ordinates be known. The control points were placed in such a manner that there would be six in each model. However, because the targets were in four rows of three (each model having two rows), problems were experienced with the second stereo model in that the left photograph was taken a moment too late and resulted in three targets not being on the photograph. The minimum requirements for a stereo model were still maintained, however, a good iterative solution could not be found in that it could only solve effectively in 2 of the 3 dimensions. This problem was overcome with the use of control points from the terrestrial photographic survey. Because the terrestrial survey control points were put in prominent places, it was possible to locate these places from the air and use those points co-ordinates. The RMS errors of the models were as calculated, they varied from 20-45 cm in X, Y and Z. A summary of results are as follows: Model No X [m] Y [m] Z [m] 1 0,446 0,539 0,457 2 0,219 0,378 0,404 3 0,224 0,296 0,222 Tab. 2. 1. The RMS errors. The results show that the accuracies obtained, on average, were better than those calculated by the C-Factor equation. This is a good result as it is below the minimum accuracy calculated using the American equation which was 0.5 m. The results are, however, larger than the estimation of errors approach. This can be explained by the fact that there are a number of factors affecting the accuracy which was achieved, these are: - the accuracy of the ground control - intersection angle of rays The principle of intersection angles is clearly understood in conventional surveying, eg. double polars should have an angle of intersection greater than 30 and less than 150. The principle behind this is that the smaller the angle, the less distinct the point of intersection of the two rays becomes. This is particularly critical in the determination of the height co-ordinates. 46 / 65

The accuracy of the ground control is less than 0.05 m as each control point was double polared in order to provide a check so as to limit mistakes. The Z coordinate has an accuracy of 0.1 m as they were fixed using vertical angles and the center of the prism. These errors, when added to the errors which are of a photographic nature, explain why the accuracies obtained are larger than those that were calculated. The results are interesting in that the first model showed accuracies that were less than the other two models. This was confirmed by redoing the model where accuracies of the same magnitude were gained. The model showed no parallax after the relative orientation, demonstrating that the greater inaccuracies were not a result of bad geometry or observation. The only plausible explanation is the targets ground co-ordinates. All the control points were double polared in order to avoid errors and the traverse that was used to put in the control points had a misclosure of 4 cm. It could also be as a result of the targets being at different heights and that this affected the intersection angles. Another explanation could be that the film of the first photograph had distorted. However, this is unlikely to cause such a large deviation in accuracies. It is possible that a combination of the above mentioned errors has caused this result. The accuracies obtained were sufficient for the project, in that a topographical survey was the intended objective of the photography. There are a number of different possibilities which could increase accuracy, if this is required. These possibilities are: 1) metric camera 2) professional film, possibly glass plates 3) application of the lens calibration data 2.3.5. Production of the final map The stereo models on the Topocart were used to obtain the spot points of the terrain. Each of these points was recorded along with its X, Y and Z co-ordinates. A total of 706 points were observed. This data was saved in an ASCII file and was then used to create a point coverage describing the area of the site. To do this, a macro called TOPO.SML was used. This macro takes the spot points which have been saved in Topocart format and converts them into ARC INFO format. This coverage was then exported to the Sun Workstation. A tin was then created using the CREATETIN command which links adjacent spot points by means of triangles. A surface was then draped over the tin using the command TINLATTICE. This command calls for a surface form to be specified. In this instance, a QUINTEC surface was used. It has a smoothing function in that it smooths the surface by interpreting between the spot points. An alternative surface called LINEAR was tried, but was found to be unsuitable in that it produced contour lines with sharp corners. Following the production of the lattice surface, a command LATTICECONTOUR 1.0 was used to generate lm contours. Other coverages were then draped over the tin to produce the final plot. These were: a) grid intersections - point coverage b) control points - point coverage c) paths of entry - line coverage The final plot was produced on A0 size paper. A scaled down version is given in Figure 2.20 top and 2.21 bottom part, on the following page. The contouring program used is not a recognized contouring package, in that it has not been derived to fit the regulations laid down for topographic mapping. However, this contouring program is suitable for the project undertaken. 47 / 65

Fig. 2. 20 The final plot of map of archaeological site part A top. 48 / 65

Fig. 2. 21 The final plot of map of archaeological site part B bottom. 49 / 65

2.4. STEREO RESTITUTION WITH DIGITAL PHOTOGRAMMETRIC STATION LEICA DVP The DVP Digital Video Plotter is a digital stereo plotter for the extraction of 3D co-ordinates captured from the stereo model. Measurements are done from the pairs of photographs, particularly vertical aerial photographs. The principles of operation are very similar to those of an analytical stereo plotter, with one very important characteristic: the images are digital and are held in a computer rather than on film as negatives, diapositives or prints (Leica DVP manual, p 8). The input was carried out, in the study, by the scanning of the negatives. In the scanning of images there is a play-off between file size and resolution. The greater the resolution the larger the file size shown in Tab. 2.2. Resolution DPI File size in MB Resolution µm 300 7.3 85 450 16.5 56 600 29.2 42 Tab. 2.2. The files size verse resolution for a 23 x 23 cm negative. DPI stands for Dots Per Inch or pixels per inch. A dot here represents the smallest photo surface to which a gray value can be given. For eg. at 300 DPI one dot equals to 85 x 85 //m. Table 1 shows a comparison between resolution and pixel size. The images used in this thesis were 2.6 MB in size. The scanned images are stored in a TIFF (Tag Image File Format) format. However, there is a large limitation in the DVP software in that it only reads TIFF format II. 2.4.1. Interior orientation on DVP As previously stated, this procedure orientates the images with respect to each other and is achieved by the use of fiducial marks. If the fiducial marks are present, then the image corners can be used. Once the fiducial mark has been chosen, the digitizer-coordinates are entered. In the case of the images used in this thesis, for the screen image corner co-ordinates which is shown in Figure 2.22. Fig. 2. 22. The final plot of map of archaeological site part B bottom. As was mentioned in the analytical interior orientation, the quality of the interior orientation affects the absolute orientation values. This again was tested on the DVP station and found to be true. 50 / 65

2.4.2. Relative orientation on DVP This was the next compulsory operation and oriented individual points on the images with respect to each other. In essence, it reconstructed the actual camera positions when the photographs were taken. This procedure of orientation follows the steps used on analog instruments. This orientation also eliminates both X and Y parallax. The relative orientation results states the Y parallax as a factor py, this gives the amount of Y parallax that cannot be resolved. A 3D model is produced from these results. 2.4.3. Absolute orientation on DVP and analysis a priori. Absolute orientation allows for measurement to be taken from the stereo model. It does this by determining the scale and position of the model so that it is identical to the situation on the ground. As in the analytical instrument, a minimum of 2 X, Y and 3 Z co-ordinates are needed. These should preferably be in the corners of the model. An a priori accuracy could not be calculated, because the DVP station had not been used on a project in the Department prior to this thesis. The estimation of accuracies was further hampered in that the calibration data of the monitor and scanner were not known. The elements that would affect the accuracy gained, would be: 1) camera lens distortion 2) film distortion 3) scanning quality 4) computer monitor resolution and stability 5) control point co-ordinates The lens distortion data is known and the film distortion can be estimated, however, the distortion due to the scanner cannot be estimated. It is assumed that the scanner distortion is low because commercial map producing companies use the firm that facilitated the scanning of the negatives for the thesis. The only estimated errors were gained from the DVP station manual. DPI 1:5 000 1:10 000 1:15 000 1:20 000 300 0.30 0.60 0.90 1.20 450 0.20 0.40 0.60 0.80 600 0.15 0.30 0.45 0.60 Tab. 2.3. Estimated errors for different DPI and scale in meters. The negatives used in this thesis were scanned at 650 DPI, so using the same scale factor 0.7143, which is applied to the ground cover by one pixel. For eg. a pixel 85/mi covers 0.426m on the ground at a scale of 1/5000. Using this scale factor the maximum accuracy of DVP station software can be calculated as follows: DPI 650, scale 1:4000, pixel size 39 µ gives maximum accuracy ± 0,11 m It is important to note that this is the maximum accuracy which the software can produce and that this accuracy ignores factors such as lens and film distortion and control point accuracy. This a priori 51 / 65

value was initially calculated for 400 DPI, which was the instruction to the company who facilitated the scanning. However, it appeared that the scanning was done at a higher resolution of 650 DPI. It was also expected that the height accuracy of the stereo model would be less than the Topocart as there would be less of a height distinction. This effect is expected to decrease with an increase in resolution. Following from this, it was expected that the accuracies from the DVP station would be 20-30 percent less than those gained by the Topocart. 2.4.4. Analysis a posteriori. Unfortunately due to the financial constraint, it was not possible to scan all four photographs, so the two photographs constituting the first model were chosen and scanned. These results are discussed below. A relative orientation was done and a standard error (or RMS) for the Y parallax was of 0.022 units. This value represents the minimum amount of Y parallax that the software can solve for the model. This value relates to the screen coordinates and scale. An absolute orientation was done producing the following results: COORDINATES X Y Z RMS 0.53 0.55 0.29 Tab. 2.4. Results of absolute orientation. The X and Y results were as expected, 10-20 percent less accurate than thode of the Topocart. The Y and Z results prompted a lot of discussion between the operator and Dr Florek in order to explain why the results were better than expected. These results confirm those gained from the Topocart. The results were surprising in they were thought to have been obtained from images that were scanned at 400 DPI, as was requested. It was later established, however, that the negatives had been scanned at 650 DPI. This went a long way in explaining the clarity of the control points and the results obtained. A point of interest was the high Z accuracy in comparison to those of X and Y. The model was repeated in order to establish whether the Z value was correct and it was. This was of interest in that the X, Y and Z accuracies were to be of the same order. Numerous suggestions were put forward to explain this. The suggestions included: a) weak geometry of the control points b) bad control point co-ordinates c) value resulting from "inertia" according to Dr Florek, this being the smallest movement of the measuring mark 2.5. PROBLEMS EXPERIENCED WITH THE RESEARCH 2.5.1. Aerial photography Only one problem was experienced during the planning, implementation and analysis of this survey. This was discussed previously, and involved the second stereo model being short of three control points. As the left photograph was taken too late, this deficiency was overcome by using the control points of the terrestrial survey. 52 / 65

2.5.2. Terrestrial photography A total of 17 stereo pairs were incorporated in this survey. Unfortunately, not all these stereo pairs provided good alignment. This was primarily due to the fact that both cameras were not perpendicular to the photo base. Also the western side of the site was sparsely covered by control points, as a result of inadequate planning. This meant the taking of long oblique photographs with the minimum number of targets. A further complicating factor was the choice of camera. Due to the limited resources available, an 80mm lens was used. This means that the lens has a narrow angle and meant that many photographs were required to cover the site. This was one of the reasons for the large number of stereo pairs. 2.5.3. The DVP station A limitation of this software is that it recognizes only one TIFF image format. As the images in this study were scanned in the MM format, a computer program had to be written to convert them to the II format. 2.6. CONCLUSIONS AND RECOMMENDATIONS 1) It is recommended that some basic principles be adhered to in the planning and taking of photographs for a survey. These principles include: a) thorough planning, in order to avoid mistakes; b) calculation of the depth of field, so as to ensure the correct focusing; c) the alignment of the camera with respect to the photo base, in order to create good 3D models; d) target size and distribution; 2) The use of terrestrial or aerial photography depends largely on the size and terrain of the site. Aerial photography is better for recording larger sites and the progress of digs, while terrestrial photography can be more easily applied as there is no need for a photographic platform. Aerial photographs also provide a good record for the reconstruction of a site. 3) Aerial photography needs to be planned thoroughly, because the photographs must work first as it would be very expensive to repeat the photography should any mistake be made. 4) The analysis of the photographs shows that the use of a good quality non-metric camera can be used for this type of project, since the accuracy obtainable is satisfactory. 5) The computer software used for the production of the final map, is not a recognized topographic contouring package, it is, however, suitable for use on projects similar to the one undertaken. 6) The estimation of errors approach in the a priori analysis proved to be a good approximation for the errors a posteriori. 7) The results of the images from the DVP station compared favorably with what was expected. However, these results are dependent on the resolution of the scanning. Lower accuracies can be expected if the images are scanned at a lower resolution, therefore the scanning resolution is a significant factor and should be taken into consideration during the a priori analysis. 8) The study cannot recommend the use of the DVP station for all types of photogrammetric survey. It is, however, suitable for use on projects similar to the one undertaken in this study. 53 / 65

9) The DVP station provides a cheaper alternative to the topographic stereo-restitutor the use on projects similar to this case study. REFERENCES AND SELECTED BIBLIOGRAPHY Adams L P, 1980. The use of non-metric cameras in the short range photogrammetry. International Society for Photogrammetry and Remote Sensing vol 14: ppl- 8 Anderson R C. A kite supported system for remote aerial photography. Aerial Archaeology vol 4: pp 4-7 Biddle M, Cooper M A R, et al, 1992. The Tomb of Christ, Jerusalem: A photogrammetric survey. Photographic Record, 14(79) pp 25-43 Burnside C D, et al, 1983. A digital single photograph technique for archaeological mapping and its application to map revision. Photogrammetric Record 11(61): pp 59 68 Butowtt R, Florek R, Sitek Z, et al, 1981, Technical standards for architecture documentations. Warszawa. Cheffins O W, 1969. Accuracy for heighting from vertical photography obtained by helicopter. Photogrammetric Record 6(34): pp 379-381 Cochrane J A. The Dunford Aerial Photographic System. Aerial archaeology vol 4: pp8-11 Cooper M A R, Robson S, et al, 1992. The Tomb of Christ, Jerusalem: Analytical photogrammetry and 3D modeling for archaeology and restoration. International Society of Photogrammetry and Remote Sensing vol 29: pp 778-785 Gala J, Rusiecki K, Walocha K, 1980. Contribution of the photogrammetry on the restoration of the ancient architectural monuments and sit of the old city Krakow. International Society for Photogrammetry and Remote Sensing vol 23 (B5):pp 221-227 Georgopoulos A, et al, 1986. Photogrammetry unwinds Ariadnes thread: Recording the archaeological site of Cnossos. Photogrammetric Record 12(61): pp 87-91 Graham R W, 1988. Small format aerial photography. Photogrammetric Record 12(71): pp 561-573 Guaangwen L et al, 1984. The study and experiment on photogrammetry of ancient architecture. International Society for Photogrammetry and Remote Sensing vol 25 (A5): pp 354-362 Hanaizumi H, Taumashima T, Fujimura S, 1994. Application of proximity stereometry to archaeology 3D shape measurement of the head of a wooden statue. International Society of Photogrammetry and Remote Sensing vol 30: pp 150-154 Harding B, 1989. Model aircraft as survey platforms. Photogrammetric Record 13(74): pp 237-240 Manual of Photogrammetry, fourth edition. American society of photogrammetry. pp 398-399 Marks A R, 1989. Aerial photography from a tethered helium filled balloon. Photogrammetric Record 13(74): pp 561-573 Robson S, Littleworth R M, Cooper M A R, 1994. Construction of accurate 3D computer models for archaeology, exemplified by a photogrammetric survey of the Tomb of Christ in Jerusalem. International Society of Photogrammetry and Remote Sensing vol 30: pp 338-344 Raven-hart R, 1967. Before Van Riebeeck: Callers at South Africa from 1488 to 1652. C. Struik (PTY.) LTD. pp 166-168 54 / 65

Sawer P, Bell J, 1994. Photogrammetric recording and 3D visualisation of Ninstints: A world heritage site. International Society of Photogrammetry and Remote Sensing vol 30: pp 345-348 Smith M J, 1989. A photogrammetric system for archaeological mapping using oblique non-metric photography. Photogrammetric Record 13(73): pp 95-105 Thorn H B, 1952. Journal of Jan Van Riebeeck: vol 1 1651-1655. A A Balkema. pp 25, 30, 40, 41, 124, 323, 357 Waldhausl P, Platzer P, 1984. Instant plans by polariod instant photography for archaeology and architecture. International Society for Photogrammetry and Remote Sensing vol 25 (A5): pp 740-745 Wester-Ebbinghaus W, 1980. Aerial photography by radio controlled model helicopter. Photogrammetric Record 10(55): pp 85-92 Winchester C, 1928. Aerial photography: A comprehensive survey of its practice and development. Chapman and Hall Ltd. pp 170-178 55 / 65

3. A COMPARISION OF A METRIC AND NON-METRIC CAMERA FOR THE PURPOSE OF DOCUMENTATION OF BUILDINGS The graphical documentation of buildings plays an important role in the general documentation of buildings. It provides accurate information about the building's structure and dimensions. This information is used by people such as architects, planners, historians and engineers in their various professions. 3.1. INTRODUCTION Of the various methods available to document buildings, photogrammetry has been widely accepted as the best method for most applications. Photographic cameras are frequently used in the recording of structures although CCD cameras and similar equipment are playing a more important role in data capture. However, for most countries the photographic camera will still play an important role in years to come because of significantly lower costs of equipment, availability of equipment and the good results that can be obtained. Traditionally metric cameras were used to accurately record structures. However, from tests (Adams L.P, 1981) on high quality non-metric cameras (Mamiya cameras used in this thesis), it was found that they are capable of fulfilling the requirements of photogrammetry. As accuracies for documentation purposes are normally in the 1 to 5cm range, it was decided to see whether a nonmetric camera was capable of achieving these accuracies. As using metric cameras is expensive, it was also decided to see whether a non-metric camera could replace a metric camera for the documentation of buildings. To do this, the two types of cameras had to be compared with respect to accuracy, cost, ease of use and other attributes. The objectives of this report are: 1) To inform the reader about documentation and its importance. 2) To determine whether a non-metric camera can be used to document buildings. 3) To determine whether a non-metric camera is more favorable to use than a metric camera for documenting buildings. To achieve objectives 2 and 3, photographs of the same structure had to be taken with both types of cameras and the accuracies compared. Procedures used and information about the cameras also had to be compared. The report begins with the major differences between metric and non-metric cameras. The importance of documentation and its applications are then discussed to give the reader an understanding of the background in which the cameras are being compared. Various existing documentation methods are then briefly discussed in this review. A large part of the report is devoted to describing the practical procedures involved to get results. The results are stated and are followed by an analysis of the results. In the analysis, reasons are suggested to try and explain the results. The thesis ends with conclusions drawn. The major limitation of this report was time. Unexpected results were obtained and because of a lack of time, tests were not able to be carried out to support the author's explanation of them. 56 / 65

3.2. MAJOR CHARACTERISTICS OF METRIC AND NON-METRIC CAMERAS It is important to note the major differences between metric and non-metric cameras. A metric camera is a camera which has been specially designed for surveying purposes. Every metric has (or should have) a calibration certificate. This certificate states information about the camera's principal distance, lens distortion parameters and fiducial marks' coordinates. This information is determined by calibration procedures. Other important characteristics of metric cameras include location of the principal point on the image plane by reference to the fiducial marks, usually large format film and flattening of the film on to the image plane at the instant of exposure. The film is flattened by one of three ways: a) The film is a flat glass plate coated with emulsion which is pressed against the focal plane by a pressure plate b) The film is a stable, flexible base with emulsion which is stuck to a flat glass plate and pushed against the focal plane by a pressure plate c) The film is sucked on to a flat plate by a vacuum and then pressed on to the focal plane. A non-metric camera is a camera which does not possess these characteristics. For this report the UMK10/1318 was chosen as a metric camera and the Mamiya C330 as a non-metric camera. The Mamiya camera, although non-metric, is a high grade camera. The main characteristics of each camera are listed below: CAMERA NAME UMK 10/1318 MAMIYA C330 Focal distance 99 mm 80 mm Effective image angle 78 40 Film size 13 * 18 cm 6 * 6 cm Focusing 3.6 m - infinity 0.3 m - infinity Tab. 3.1. Characteristics of UMK and Mamiya cameras. Cut film was used for the UMK and roll film was used for the Mamiya. 3.3. DOCUMENTATION OF BUILDINGS In order to understand the context in which the cameras are being compared, it is necessary to know a bit about documentation. For the purpose of this report, documentation is the accumulation of information about buildings in the form of plans, maps and sketches. It involves the measurement of buildings and portions of buildings. This information forms a vital part in the general documentation of buildings, where the aim is to heighten the understanding of a building's use and history and to show why it is like it is and what changes have been made to it. There are various methods for documenting buildings, some of which will be reviewed later on. However, the photographic camera has been used the most to document buildings as the whole 57 / 65

structure is recorded and the data can be accessed at any time after the photographs have been developed. There are many reasons for documenting buildings, the main one being that documenting aids in the understanding and illustration of histories of buildings, their plans, structure, development, use and decoration. This information is required by architects, planners, historians, engineers in their various professions. Some other reasons are: 1) Documentation is required in the case of the destruction of a building due to fire, earthquakes, unstable ground or other causes. 2) Buildings which are of value, be it architectural or historical, are all affected by the ravages of time, weather and other destructive forces. In order to keep these buildings in satisfactory condition by means of restoration, it is necessary to have accurate information about the building before the restoration process begins, hence the need for documentation. 3) Architects need these plans when they are designing plans for restoration. 4) Town planners require this information so that they can base planning and other decisions on accurate information. 5) It is needed in grant applications where accurate records are needed as supporting evidence. 6) Planning authorities need to know the historical and environmental resources of their districts so that they can take these into account when developing local and strategic plans and in considering how to develop amenities. 7) Municipalities need records in assessing the condition and potential of buildings. 8) Historians need records to show how people lived, worked and designed and built in the past. 9) Documentation is required to recognize structural faults of buildings. As can be seen, there are many reasons why it is necessary to document buildings. The above mentioned are just a few. 3.4. REVIEW OF BUILDINGS DOCUMENTATION APPLICATIONS As part of the background for this report it is interesting to see how documentation was originally done as it helps us to appreciate the usefulness of photogrammetry. In this next section, traditional surveying methods for documentation are discussed as well as classical photogrammetric methods and more recent advances in photogrammetry. The various categories for documentation surveys are discussed first. 3.4.1. Documentation survey categories There are three categories of survey for the documentation of buildings. They are: 1) rapid, simple surveys 2) precise surveys 3) very precise surveys Each category deals with certain aspects of documentation and has certain accuracy requirements. Rapid surveys are used for, among others, preliminary studies for restoration or development, inventory work and study of the history of art. Accuracy requirements are in the 1 to 5 cm range and 58 / 65

scales of plots of the buildings are normally between 1:100 and 1:200. The detail displayed is restricted to the main architectural lines such as elevations and vertical sections. The so called precise surveys are the most common for documentation purposes. The applications of these surveys will be discussed in more detail in the next section. Accuracy requirements are in the 2cm range. Plots of buildings are usually made at scales of 1:100 to 1:50. Features are plotted at scales of 1:20 to 1:10 and details are plotted at scales of 1:5 to 1:1. Very precise surveys require accuracies in the single millimeter range. Examples of such surveys have been the documentation of statues for their reproduction without making a cast of the original, determination of the types of tools used by ancient man from the marks caused by their tools on surfaces and determination of the degradation of stone over time. There are various methods for documentation, the two main ones being traditional surveying methods and photogrammetric methods. 3.4.2. Surveying methods The traditional hand measurement was documentation method. It involved the direct measurement of a structure on site and the preparation of scaled drawings from the dimensions obtained. Hand measurement has the advantage of being carried out by non-specialists with simple inexpensive equipment. It also gives the person in charge of the recording a familiarity with the building which could not be gained by reading other people s records. Hand measuring is best suited for the measurement of buildings of a modest size which are not badly deformed. Buildings which have walls out of plumb or alignment or a sagging roof cause some difficulty when it comes to measuring them. The recorders generally require physical access to points from which measurements can be made and this causes difficulties when tall or large buildings need to be documented. The traditional equipment consisted of rods, tapes, chains, plumb lines etc. Use was also made of theodolites, either to determine positions of points on surfaces or to set up control from which measurement by tapes could be used. With the advent of EDM instruments, greater accuracy could be obtained but the costs of recording increased due to the expense of the instruments. Hand measurement is still one of the cheapest and most accurate ways of documenting buildings. It is often invaluable for filling in essential data unrecorded by other techniques or where the use of other techniques is uneconomical. The disadvantages are the expense in manpower and time. If the work is to be done most efficiently, at least two people, preferably three are required for the job. There is a danger of inexperienced operators not recording a key dimension. Hand measurement is not suited to the storage of raw data. 3.4.3. Photogrammetric methods Photogrammetric surveying methods have been widely accepted as being the best methods available for, among others, the documentation of buildings. It allows the accurate measurement and plotting of 3D structures from their 3D images formed by stereoscopic photography. The traditional and still very much used recorder, is the photographic camera. This makes use of a light sensitive chemical emulsion to record the image. Traditionally, metric cameras were used for photogrammetry as these cameras have accurately calibrated lenses of the known property. However, more and more use is being made of non-metric cameras due to their versatility. In order to obtain measurements about the structure photographed, there are two main methods for doing this: Using an analogue stereo-plotter or an analytical stereorestitutor. In both cases, two overlapping photographs are placed on the machine but their relative positions with respect to each other and their orientation in space at the time of photography are reconstructed differently. With the 59 / 65

analogue plotter, the photographs are manipulated manually in the processes of relative and absolute orientation. Once this has been done, measurements of the structure can be made. With the analytical plotter, the image points are related to the model by an on-line computer which maintains stereovision for the operator. The more recent developments in image recording have been the use of CCD cameras and other similar devices. The CCD camera has a chip in place of the emulsion. This chip consists of rows of tiny photosensitive detectors which record the amount of light falling on them. This is then converted to a number from 0 to 255 where each number corresponds to a shade of gray. The image which is now in digital form is stored in the computer memory and later stored permanently on disc. The image which is normally seen on a video monitor consists of many tiny picture elements or pixels of uniform photo density. The processing of digital images is completely analytical. The main advantage of digital images over photographs is that no emulsion is used and therefore no time is spent developing the images. Instead, the image can be recorded and almost instantly be worked with and measurements made. Another big advantage is that the image can be manipulated to enhance certain characteristics. Therefore, if your image is not of good quality it can be improved. With a photograph, if you have a bad image you have to re-photograph the object if you want a better image. 3.5. APPLICATIONS OF PHOTOGRAMMETRY AND SURVEYING FOR THE DOCUMENTATION OF BUILDINGS There are many applications for documentation. They can be loosely categorized into the following fields: 1) Architectural analysis of monuments 2) Conservation and Restoration 3) Recording of historical monuments 4) Development of facades 5) Surveys of decorations of monuments 6) Archaeological surveys 3.5.1. Architectural analysis of monuments This would include the study of architectural lines necessary to understand the building ie. how the lines contribute to the overall impression of the building. These surveys would include interior and exterior elevation views as well as horizontal and vertical sections. They would help to understand the structure of the building. These surveys have to be precise in order to pick up deviations from the geometry of the lines. The reason for this is that often these deviations were intentional as they are intended to add to the overall effect and character of the building. An example of such a survey is the study of sixth, fifth and fourth century BC Greek architectural monuments (Badekas,1974). Certain temples built by the Greeks in approximately 500BC are still surviving today. According to the writer they "reveal exceptional precision, impressive technical skill and a graceful interpretation of forms", in other words they were very impressive from a technical and art point of view. However, these monuments often had deviations from strict geometrical forms which were not noticed at first glance. Often these deviations were intentional and were aimed at enhancing the overall impression and style of the monument (they helped to produce "inner harmony") 60 / 65

Before such a monument could be restored, it would be necessary to determine whether such deviations were intended when the building was first built or whether they resulted from movement over time. These deviations can take the form of inclinations of lines and planes which are supposedly vertical, deviations from apparently straight lines or curves. If the optical refinements are ignored in the restoration, the most sensitive parts of the monument (i.e. those which contribute to its aesthetic value) could be affected and this would detract from the overall impression of the monument. An analysis of such a monument is crucial before any restoration can take place in order to preserve its character, style and aesthetic value. Such an analysis makes use of large scale maps to pick up characteristics as well as verbal descriptions. Another example in which analysis would be required is the determination of the geometrical form of parts of buildings (Badekas, 1974). In this investigation, four rooms of different historical buildings were investigated to see what caused their particular acoustic effects. The structures in the rooms were measured and their geometrical form and parameters were determined using best fitting shapes such as ellipsoids of revolution, hyperboloids and others. Their influence on acoustical affects was then investigated. 3.5.2. Architectural Conservations and restorations of buildings Conservation and restoration has become very important in preserving a country's cultural and architectural heritage. Due to time and the effect of the elements, buildings slowly become delapidated and fall apart. As many old buildings are of architectural value due to their design or structure, it is important that they be preserved by restoration. Documentation of buildings plays a big role in the conservation and restoration of buildings as it provides visual information about the building in the form of accurate sketches. Accurate measurements and descriptions of the various parts making up the building are required if it is to be successfully restored and retain its architectural value. When such operations are carried out, the architect or conservationist in charge will specify the parts of the monument to be treated, the nature of the measurements to be made and the documents to be produced. Architectural lines, construction methods as well as deformations are recorded. From the measurements made, information such as inclination of walls and pillars, profiles of arches, shapes of vaults etc. is determined. An example of where such surveys were used for the restoration and conservation of buildings was in the many European countries, where every cultural monument had to have a certificate indicating its historical data and artistic characteristics. These data were systematically updated with the latest results of historical investigation, soundings and architectural surveys. The results had to be plotted and presented in the form of diagrams. These records would be used to restore buildings in the event of them being destroyed. 3.5.3. Recording of historical buildings These surveys are normally carried out as part of a general documentation of a country's heritage. The surveys are generally detailed, documenting both the interior and exterior of historical monuments. They are used together with written reports of historical, social and cultural significance for historic studies, comparative studies, feasibility studies and restoration purposes. They involve considerable effort and expense and are normally only carried out by a government funded agency. Priority is given to collecting all the information necessary for making plans. The actual drawing up of plans follows as soon as possible. The public is given access to these records in order to conduct whatever studies they wish to. The Canadians (Badekas, 1974) started a general recording of historical monuments and sites in the 1960's. It was a federal Government Conservation program which came about due to the growing public demand for the preservation of historical land marks. Canada has many historical land marks 61 / 65

due to the many peoples that have lived in the country, some being Indians, Eskimos and French settlers. The Canadians developed an inventory of historical sites which they later put into a computer information system called INFOTEQUE. The written information was supplemented by accurate graphical information. This system allowed the quick, accurate retrieval of information about any recorded historical monument. The information was gathered by teams consisting of historians, archaeologists, conservators, architects and engineers. The information was gathered by hand recording and photogrammetric recording. Hand recording consisted of the following: 1) Preliminary report: This consisted of scaled sketches of floor plans and elevations of the monument accompanied by a descriptive report with color photographs of the monument. 2) Reference data survey: This gathered additional information from surrounding buildings similar to the monument (in age, design etc.). 3) Detailed precision hand recording: This information was aimed at providing the plans for the precise reproduction of the monument. A 3D grid was superimposed on the monument by theodolite from which measurements of the inside dimensions were made, enabling accurate plans to be made. 4) "As built" records recorded changes made to the monument during restoration. The photogrammetric recording consisted of rectified photography of simple flat facades which were later combined with drawings. Architectural stereo photogrammetry was used when the job became impossible for the hand recording teams due to higher accuracy requirements and greater work load. 3.5.4. Surveys of decorations of monuments Documentation in the form of accurate sketches play an important role in the conservation and restoration of decorations. Decorations can be murals painted on walls of churches, statues, wood carvings etc. Many countries in Europe for example, have beautiful, medieval art tucked away in ancient churches, cathedrals and castles. Many of these works are priceless national treasures which are slowly decaying due to the effects of time, weather and other destructive forces. The governments of these countries want to preserve these treasures and documentation plays an important role here. A good example of the application of documentation in the preservation of decorations is that of the restoration of the "Candlemass ", shown in Fig. 3.1. a mural painted in the 1400's on a church wall in Bulgaria (Badekas, 1974). This mural was painted over another one which had been painted in 1259. In order to study the older mural, it was necessary to remove the top one and place it somewhere else. The problem arose in the creation of a base for the mural which would be identical to the previous one. It was important that the bases were identical in order to prevent any deformation of the composition. Documentation provided the answer for this problem. It provided a contour map of the wall with 2 mm contour intervals with the outline of the mural drawn accurately on it. This permitted the construction of a model of the " folded wall " over which the mural could be placed. This method of restoring murals could also be used if the base is decaying and will cause the eventual destruction of the mural. 62 / 65

Fig. 3.1. Photogrammetric map of a mural painting of the ancient church of Boyanna, Bulgaria. 3.5.5. Surveys of facades Surveys of facades or building exteriors are carried out for the systematic documentation of harmonious architectural groups formed by series of houses in a street or on a square in ancient urban areas or towns. An example of this was a survey done by UCT of a facade of an old Cafe in Cape Town which was to be demolished (fig.2). The Cafe was of architectural value and was surveyed so that the replica of it could be reconstructed at any time in the future. 3.5.6. Surveys of archaeological sites These surveys deal with the documenting of monuments discovered in archaeological digs. They provide accurate maps of the layouts of sites of eg. ancient towns or buildings which have been unearthed for the study by the various experts in those fields. They also provide accurate diagrams for the various artifacts unearthed, which are used together with all the written information to provide general recording of that artifact. An example of such a survey was there in the Western Cape. Due to a storm along the east coast, a wreck was uncovered by the sea at Plettenberg Bay, RSA. The team only had a matter of hours to gather information about the wreck before the sea covered it up again. Using tapes and a non-metric camera, sufficient accurate information was gathered to enable an accurate sketch of the wreck to be made. From this sketch, measurements were made which helped historians and archaeologists discover what kind of ship it was and its historical background. 63 / 65

Fig. 3.2 The UMK metric camera Fig. 3.3. The Mamiya non-metric camera 64 / 65

3.6. CONCLUSIONS From the conclusions drawn from the analysis and comparison of the two cameras, the following major conclusions were drawn. 1) Should the indications of the accuracy of the Mamiya camera prove correct, then the Mamiya camera, as an example of a non-metric camera, can be used successfully for the documentation of buildings. 2) The Mamiya camera requires calibration of the lens and/or more control to ensure acceptable results. 3) Operation procedures and costs make the Mamiya camera more favorable to use than the UMK. BIBLIOGRAPHY 1. Photogrammetric Survey of Monuments and Sites, ed. J Badekas. Athens: North Holland Publishing Company, 1974 2. B Hallert, Photogrammetry - Basic Principles and General Survey. New York, Toronto, London: McGraw-Hill Book Company, Inc, 1960 3. E M Mikhail." Introduction to Metrology Concepts". Non-topographic Photogrammetry. ed. H M Karara. Virginia: American Society for Photogrammetry and Remote Sensing, 1989 4. L P Adams, "The use of non-metric cameras in short range photogrammetry" Photogrammetria, 36 (1981), pp 51-60 5. W Faig, "Non-metric and semi-metric cameras: data reduction". Non-topographic Photogrammetry. ed. H M Karara. Virginia: American Society for Photogrammetry and Remote Sensing, 1989 6. S F El-Hakim, A Burner and R Real. "Video technology and real-time photogrammetry" A/ontopographic Photogrammetry. ed. H M Karara. Virginia: American Society for Photogrammetry and Remote Sensing, 1989 7. International Council on Monuments and Sites (ICOMOS), "Guide to recording historic buildings." Great Britain: Butterworth Architecture, 1990 65 / 65