LIMEZ - Photogrammetric Measurement of Railroad Clearance Obstacles

Transcription

1 LIMEZ - Photogrammetric Measurement of Railroad Clearance Obstacles Heinrich Schewe 1, Jürgen Holl 2, Lothar Gründig 3 1 Photogrammetry Consulting, Hausen a.t., Germany 2 Technet GmbH, Stuttgart, Germany 3 Institute for Geodesy and Photogrammetry, Technical University, Berlin, Germany 1 INTRODUCTION Europe is growing together. This is a fact, not only in the field of politics, but also with railway traffic. In the future many European trains will use the German rail network. In many cases the size of these trains do not correspond to the norm of the German trains. Furthermore within the next few years the Deutsche Bahn AG (DB AG) is planning the expansion of the carriage of goods. For the safe and optimized control of such transportation, it is of special interest to register the geometry of rails, network topology and the topographic data. The crucial criterion for the safe operation of a rail network is the obstacle clearance area, that is the area within which a train can drive unchecked. To determine this, in Germany the obstacle locations are being checked or measured for the first time since 1996 with photogrammetric methods. The geometric and attributive data determined are being permanently stored as clearance obstacle profiles in the data base of DB AG. In this paper the reasons for the photogrammetric measurement and the special conditions for photogrammetric analysis are illustrated. 2 MEASUREMENT METHODS The Deutsche Bahn AG developed different methods to measure clearance obstacle profiles:?? Profil Meßtriebwagen (ProM)?? Photogrammetrisches Einzelbild-Lichtraum-Meßsystem (PELiM)?? Lichtraumprofil-Meßzug (LiMez) To record clearance obstacle profiles from a tilting train, photogrammetric methods are preferred. While the PELiM system often is used in the area of railway stations, the LiMez-system is an approved method outside of railway stations. The succeeding explanations refer to the LiMez system. The advantages of the photogrammetric methods are: 1. Short object occupation time: To record narrow passages it is not necessary to stay for a long time at the object. The photogrammetric analysis is made afterwards using the images made at the site. The photographs are made by driving past very quickly. Consequently the traffic schedules are not excessively disrupted. 2. High accuracy: If the cameras used and the measurement setup are chosen well, high accuracy for the clearance obstacles can be achieved. 3. High discretization level: Decisions concerning which details are detected and which frequency of points is made during the photogrammetric analysis. 4. Permanent record: The obstacle locations are stored permanently on images. An eventual remeasurement of specific details is possible all the time. 5. Non-tactile method: Obstacle objects can be measured without expendable targets.

2 The enumerated articles are casting for the photogrammetric measurement of railroad clearance obstacles by DB AG. Conventional geodetic measurement methods certainly compete on some points, but with regard to the short object occupation time photogrammetry is definitely the more advantageous. 3 THE LIMEZ II AND ITS PHOTOGRAMMETRIC SYSTEM The LiMez II consists of a combination of locomotive and a trailer on which the photogrammetric equipment is placed. In the locomotive the essential components, namely the control desk and the measurement features are placed in the cockpit. On the trailer the cameras and the frame of control points are mounted. The whole formation is composed of the following components: video equipment, photo system, axis of measurement, narrow detector, wire measurement and the computer system [Blondeau, Steinfort 1999]. The succeeding explanations refer to the features of the photogrammetric system. 3.1 Cameras During measurement runs of LiMez II the images are taken by 2 synchronously initiated small format cameras which are placed a distance of 2.5 m to each other. The cameras have a 3x3 reseau grid. The range of focal length is 31 mm. Figure 1: Left and right image made by the photo system of LiMez II 3.2 Frame of control points The frame is mounted on the trailer a distance of 11 m from the cameras. The 22 control points on the frame, which define a preliminary coordinate system, are located in 3 planes and serve for the exterior orientation.

3 3.3 Rail coordinate system The final coordinates of the obstacles have to be delivered in the rail coordinate system. This system is defined by the middle of the rails and the upper edge of rails (v. Figure 3). The reference of the frame system and the rail system is given by 6 extra points on the frame. These points are mounted on movable levers. Consequently the points are known in the frame system as well as the rail system and are used by the Helmert transformation as identical points. Figure 2: Frame of control points Figure 3: Rail coordinate system 3.4 Area of measuring The area inside which the objects have to be detected is given by the frame of control points and the obstacle clearance area (v. Figure 4). If an object is within the area 3 m in front of the control point frame or 3 m behind the control point frame and comes within 10 cm of the clearance area, the object has to be measured. The whole object has to be measured even if it is only partially in the measuring area. 3.5 Locus of obstacles Figure 4: Obstacle clearance area The description of the locus of an obstacle is given in terms of route distance or chainage. During the measuring runs this variable must be determined. Therefore the LiMez has sensors, which are synchronized every 200 m to time signals using the videos of exactly measured objects. Consequently for each image there exists a locus for the frame of control point with the accuracy of 0.5-1m.

4 3.6 Correction of radius The reference axis for the description of the obstacles is the rail axis. In contrast to the photogrammetric measurement which uses a cartesian coordinate system, the rail axis generally is curved. Particularly in tight curves deviations up to 5 cm occur between the cartesian x-axis of the photogrammetric measurement and the rail axis. The deviations have to be corrected acorrectly. 3.7 Required accuracy Figure 5: Radius correction The required accuracy for the measurement of the obstacle locations is 2 cm in y- and z-direction and 1 m in x-direction. 4 AUTOMATED MEASUREMENT USING PICTRAN-L In this section the highly automated evaluation of clearance obstacles profiles using Pictran-L is described. Pictran-L is a specially adapted version of the digital photogrammetric system Pictran- D/E for the evaluation of obstacle clearance profiles on the basis of LiMez-data. The specific and known conditions (cameras, control points, control point targets) allow several job steps to be accelerated (e.g. reaseau mark measurement and control point measurement). The ultimate object evaluation has to be done by the operator. For the point measurement there are different facilities available. These facilities make the evaluation much easier and faster. In this regard the automatic point measurement with least squares template matching, the identification of homologous points with epipolar lines and the determination of 3D-coordinates from measurements in only one image using object planes have to be mentioned. The several job steps are described in the following section. 4.1 Model creation and import Firstly the photo-cd images delivered from the DB AG are associated and converted to the Pictran-L image format (btf). Homologous images are identifiable on the basis of the record number. Additionally, the macro-files and directory structures which will be needed later are created automatically. 4.2 Macro-interpreter To automate the flow of work a macro interpreter was implemented. The interpreter allows the handling of file commands. Macro files exist for the interior orientation, automatic control point measurement, exterior orientation and for the evaluation of obstacles. 4.3 Interior orientation The macro for the interior orientation starts the measurement of the 9 reseau points. First two reseau points have to be measured manually. Thereafter the other reseau points are measured automatically

5 and the parameters of the interior orientation are determined. The control is made visually, whereby the possibility of corrections and manual input exists 4.4 Exterior orientation The exterior orientation is the fully automatic result from the attention handling of the correspondinig macro. The points of the frame are approximately specified and determined with least squares template matching. Points which have not been measured (e.g. points hidden by reseau marks) are determined manually in a finishing step. The points of 100 images (2800 points) can be processed in this way in approximately 30 minutes. The next step is the calculation of the exterior orientation which is the result from the integrated bundle block adjustment. The results of the adjustment have to be checked for blunders in the observations, which is supported by data snooping. Consequently a sufficient control of the exterior orientation is provided. 4.5 Determination of obstacles Pictran-L is configured by the use of the obstacle evaluation macros so that the operator can begin immediately with the determination of the obstacles. The oriented images are opened and positioned on screen. For the evaluation there are several facilities placed at the users disposal (e.g. epipolar lines or object planes to determine coordinates). The measurement area is displayed in 3 views (scratch view, lateral view, plan view) and is available during the measuring session. That way, the decision whether an object is within the measuring area is easier to realize. Furthermore it is easily possible to detect and correct eventual evaluation errors. For each measured object point the accuracy of ray intersections is shown on the screen. The contour of objects is determined by points and graphical objects (polygons). Simultaneously with the detection of the geometry the attribute data of each object of a narrow passage are stored in the Technet-LiMez-Database (Ms Access) (e.g. CD-number, route number, date of photograph, comments of evaluation etc.). Figure 6: Photogrammetric measurement using Pictran-L

6 4.6 Export The merge of the attributive data of the Technet-LiMez-Database and the geometrical description of the obstacles from Pictran-L as well as the delivered route length (kilometre) of DB AG is made after the photogrammetric evaluation by LiMez export. The interface between the clearance obstacle profile database of DB AG and Pictran-L is a file in ASCII format. This file is generated together with hybrid images. In the hybrid image there are 3 profiles of obstacle clearance area displayed. In a completing step for each narrow passage a plot to scale 1:25 is generated. In this plot the obstacle with its dimensioning and special attributive data are mapped (see Figure 8). Figure 7: LiMez-Database Figure 8: Result as plot

7 5 CONCLUSIONS With the LiMez II, an advancement of the prototype LiMez I, an efficient system for the measurement of railroad clearance obstacles is available. In particularly the short object occupation time is an essential criterion for a photogrammetric system. The analysis software Pictran-L was specially adapted for the LiMez data so that the evaluation is highly automated and the objects with their attributes can be fed directly into the data base of DB AG. The software has demonstrated its efficiency through the evaluation of narrow passages over the past 3 years. REFERENCES Images: Deutsche Bahn AG, Tölg, T., Essen Blondeau J. und Steinfort, F., Limez II der Lichtraummeßzug der Deutschen Bahn, Der Eisenbahningenieur, 50 (1999) 2, S Deutsche Bahn AG, Erfassung von Lichtraumprofilen mit Limez I Leistungsbeschreibung Gründig, L. and Bühler W., Zur Näherungswertbestimmung und Bündelausgleichung von Konvergentaufnahmen, Bildmessung und Luftbildwesen 53, 6. Schewe, H., A PC-Based system for digital close range photogrammetry, First Turkish-German Joint Geodetic Days, September 1995, Istanbul Schewe, H., Bauwerkserfassung und Dokumentation mit digitaler Photogrammetrie und CAD, DVW-Seminar tech 94, Berlin technet GmbH, PICTRAN-D/E, User manual for integrated photogrammetric analysis software (3D-Compilation), technet GmbH, Maaßenstraße 14, D Berlin, Germany, (1995) technet GmbH, PICTRAN-B, User manual for integrated photogrammetric analysis software (Bundle Adjustment), technet GmbH, Maaßenstraße 14, D Berlin, Germany, (1995)