AN INTEGRATED MOBILE MAPPING SYSTEM FOR DATA ACQUISITION AND AUTOMATED ASSET EXTRACTION

AN INTEGRATED MOBILE MAPPING SYSTEM FOR DATA ACQUISITION AND AUTOMATED ASSET EXTRACTION T. Kingston a, V. Gikas b *, C. Laflamme a, C. Laouche a a GEO-3D Inc, 9655 Ignace St., Suite L, Bossad (QC, J4Y 2P3, Canada info@geo-3d.com b Dept. of Rual and Suveying Engineeing, National Technical Univesity of Athens, 9 H. Polytechniou St., Zogaphos, Athens, 1578, Geece vgikas@cental.ntua.g Commission V KEY WORDS: Mobile mapping, Senso Integation, Videogaphy, Asset Extaction ABSTRACT: In ecent yeas, public and pivate oganizations woldwide ae facing a continuously inceasing demand to build and maintain the asset inventoy of thei infastuctue netwok. This is due to standing legislatue o is associated with opeations elative to maintenance, pocuement, taffic, valuation o safety and emegency esponse issues. In esponse to this ugency, today s technology allows the integation of vaious sensos that enable efficient poducts fo mobile mapping solutions. Geo-3D is a leading povide of geomatics and GIS data acquisition hadwae and softwae solutions, who woks closely with clients and academia to optimize poducts and solutions. The Tident-3D solution is a geoefeenced land videogaphy system that utilizes the latest geneation of positioning sensos (GPS, INS, DMI, high-esolution digital cameas, lase scannes and photogammety to ceate an advanced tool fo lage-scale data collection and asset management. The most ecent developments of the system ae automated oad sign detection and tansvese slope detemination. Futue developments will include pavement makings in the automated pocess. In this pape, Tident-3D technology and its advanced featues ae pesented and discussed in the fame of collaboation with the National Technical Univesity of Athens (NTUA, Geece. 1. INTRODUCTION A oad database consists of a dynamic inventoy of geoefeenced assets and thei attibutes, as well as oad geomety featues such as centeline mapping and oad pofile infomation. Most of this infomation can be collected using diffeent suveying techniques. In ecent yeas, the accuacy equiements and the amount of infomation necessay to build and maintain a oad inventoy have inceased dastically. This has caused manual field measuement techniques and taditional pocessing methods to give way to adically new solutions. Mobile mapping systems epesent an advanced technique fo the dynamic inventoy of oad netwoks and all of thei suounding featues. These systems integate advanced navigation sensos, digital imagey equipment, and poweful pocessos to ceate digital maps that include both the oad s geomety and oadside assets. Tident-3D is a geoefeenced digital image captue and extaction system, designed and developed by Geo-3D Inc. fo the pupose of pefoming the inventoy of oad infastuctue assets and thei geomety. The system elies on state of the at digital imagey coupled with advanced positioning systems and photogammetic algoithms [Laflamme et al, 24]. A key element that diffeentiates Tident-3D technology fom simila systems is centeed upon its ability to poduce geneic and scalable solutions, which ae based on an open achitectue [Laflamme et al, 26]. As Tident-3D is not tied to any specific band of camea, positioning system, etc., the uses have the ability to customize the system to meet thei needs and budget. Likewise, a vaiety of sensos can be integated into the Tident-3D solution, fom pavement analysis applications to lase scannes. This povides even moe flexibility to the use, while giving Geo-3D the oppotunity to collaboate with vendos and academic institutions in ode to design and assemble its systems to best meet maket needs. Futhemoe, Tident-3D end poducts ae suitably customizable and can be expoted fo use with thid paty softwae modules. An example of this is the expotation of vehicle navigation data fo geneating a centeline geomety database. 2. DATA ACQUISITION SYSTEM 2.1 Hadwae Components Tident-3D can integate most types of positioning systems that ae commecially available; howeve, fo pojects that exact stingent positional accuacy, the POS LV fom Applanix is the poposed solution [Schezinge, 23]. The POS LV navigation system consists of a single and dual fequency GPS eceive, an antenna mounted on a specific location on the oof of the suvey vehicle, an Inetial Measuement Unit (IMU and a pecise Distance Measuing Instument (DMI. The IMU is compised of thee acceleometes and thee gyoscopes. The data fom the GPS eceive and the IMU is passed though an advanced Kalman Filte algoithm to detemine the optimum blended navigation solution accoding to the pocessing scheme shown in Figue 1. By filteing the GPS data with the IMU data, it povides a moe obust solution to noise fom multipath and GPS shadows. In this egad, the total loss of GPS signal, o even small degadation in signal, will not impede the collection of continuous positioning tace. The DMI is also * Coesponding autho

used by Tident-3D technologies fo tiggeing the image captues at fixed distance intevals. tiggeed images and lase-scanning shots to within.1 ms, due to the 1µs esolution of the lase s clock. Moeove, an electonic inteface is used to dispatch tigge signals coming fom the seve to all installed cameas. This ensues signal quality, noise eduction and pope camea synchonization. Thus, each image is then tagged with the appopiate GPS position. 2.4 Camea Calibation 2.4.1 Inteio camea calibation: Machine vision cameas do not usually geneate imagey on which pecise measuements can be made. Theefoe, a calibation must be pefomed to detemine the intenal paametes of the camea. These include the focal length, the position of the pincipal point, the pixel size and spacing, and the adial and tangential lens distotion. A calibation cube with known taget and camea locations is used fo the calibation. As shown in Figue 2, a seies of images of the cube ae taken fo each known camea location. Once image acquisition is complete, obsevations ae made on the images to detemine coodinates (x, y of all visible tagets. Finally, all obsevations and known infomation ae gatheed into a data input file. This file is pocessed using camea self-calibation softwae that is based on a bundle adjustment algoithm. The following geneic obsevation model foms the mathematical basis fo inteio camea calibation [Slama, 198]: Figue 1. Vehicle navigation pocessing scheme (Schezinge 23 Typically, images ae geneated with one, o multiple, digital (CCD cameas offeing a vaiety of pixel esolutions: fom the common 128x96 to 248x248 and moe. The image s high esolution allows the images to be zoomed in on to view specific details. A multispectal camea has also been integated. The data acquisition system makes it possible fo the use to maintain the visual quality of the imagey though built-in camea and image contols, such as camea shutte speed, and white balance. Depending on specific poject equiements, the data acquisition system can integate one o multiple 2D lase scannes. Obsevations made on distance, angle and intensity paametes can be used to geneate a dense gid of 3D points. As detailed in Section 4, this offes a significant potential fo automation in a numbe of data extaction pocesses. Futhemoe, it is possible to couple Tident-3D technology with othe types of sensos, such as pavement pofiles. x x = f 11 31 y y = f whee 21 31 ( X X + 12( Y Y + 13( ( X X + ( Y Y + ( 32 33 ( X X + 22 ( Y Y + 23( ( X X + ( Y Y + ( 32 33 (1 f= focal length x, y= object coodinates in image coodinate system X, Y, Z= object coodinates in gound coodinate system x, y = image coodinates of the pincipal point X, Y, Z = coodinates of pojection cente ij = tansfomation matix coefficients, i,j= 1,,3 2.2 System Achitectue The data acquisition system is based on a client-seve achitectue used with multiple sensos (cameas, lase anging, etc.. The seve tigges all cameas fom the same signal souce, ensuing images acquisition is synchonized. The GPS eceive is connected to the seve, which computes GPS time tags fo the tiggeed digital fame and sends this infomation to all connected clients. The clients ae esponsible fo contolling the cameas, lase scannes and othe sensos and displaying data fo quality contol. 2.3 Data Synchonization Data synchonization is based on the use of the Pulse pe Second (PPS geneated by the GPS unit. This synchonizes Figue 2. Inteio camea calibation This application outputs the necessay inteio camea paametes that will allow optimal accuacy obsevations on the full image suface. 2.4.2 Exteio paamete calibation: The second calibation step focuses on the exteio paametes, the esults of which ae used to efine installation paametes on the vehicle. These paametes include the oientation of the camea, as well as

offsets fom the positioning system (typically GPS antenna, IMU o some othe fixed point to the camea, known as the efeence point o oigin. A set of known taget points is also equied. Taget points ae defined using conventional suveying methods o a dual fequency GPS eceive with postpocessing. Obsevations ae made on the images to detemine image coodinates (x, y of all visible tagets. Finally, all obsevations and known infomation ae gatheed into a data input file, which is pocessed using an in-house camea calibation tool (Figue 4. The softwae outputs the necessay exteio camea paametes, allowing fo optimal accuacy measuements of gound point coodinates. Contol points Figue 5. Steeoscopy using dual (left and single (ight camea 3.2 Road Geomety Extaction As stated peviously, the pocessed data poduced by Tident- 3D softwae can be used in a divese vaiety of applications. In this egad, it is poposed that lase-scanning data combined with vehicle navigation data can be used to extact centeline geomety in the fom of design alignment elements (staight lines, cicle acs and clothoids. Fo this pupose, two-way spatial data needs to be collected in opposite diections and combined to geneate centeline locations. The algoithm adopted fo the geometic modeling of oad axis elies on the combined use of the beaing diagam and the hoizontal alignment, o plana dawing of the oad axis [Gikas and Daskalakis, 25]..25.2.15 Figue 4. On The Fly (OTF softwae calibation tool 3. FEATURE EXTRACTION 3.1 Manual Featue Extaction The Tident-3D Analyst softwae is used to analyze and intepet the data and imagey collected by the suvey vehicle. The application s use inteface featues the ability to position any object visible on the imagey and to measue objects in thee dimensions. Fo this pupose, a suite of steeo photogammetic algoithms is used to locate objects that appea on a conjugate pai of images. Notably, the geatest asset of the poposed method is that only one camea is equied to position objects. The paadigm is to obtain a steeoscopic view using two cameas. A fixed steeobase is equied to when thee ae two points of view of the same object. In contast, the poposed methodology enables the second point of view to be geneated by the same camea. In this case, the steeobase esults fom subsequent camea locations associated with subsequent vehicle positions. This concept is depicted in Figue 5. The steeoscopic base can be inceased o deceased to optimize the tiangulation by modifying the lag between two etained images. It is theeby possible to pefom measuement and positioning opeations in thee dimensions fo objects that ae located both close to and fa fom the suvey vehicle without losing accuacy. Futhemoe, a numbe of featues and plugins ae available with Tident-3D Analyst. These include tools fo image extaction at egula intevals, use of vocal annotations, ODBC connectivity and GIS laye elations linking data layes to one anothe and thus, allowing bette data encapsulation. as built - model (m.1.5 -.5 -.1 -.15 -.2 15. 15.2 15.4 15.6 15.8 16. 16.2 16.4 16.6 16.8 stationing (km Figue 6. Road axis geomety: as-built minus model In effect, the pime use of the beaing diagam is to identify the type and location of the stat and end points of adjacent geometic elements; wheeas the hoizontal alignment plot is used fo computing the values of the design paametes, such as the cicle adius and the clothoid paamete. Fo this pupose, an iteative egession algoithm is used that is based on the genealized least squaes method. Figue 6 shows compaative esults fo a 1.5 km long oad segment consisting of two lanes in each diection. Moe specifically, it shows that the deviations (pependicula distances deived between the asbuilt plans and the geometic modeling softwae ae consideably small; less than.2 m and the mean eo is even smalle. 3.3 Automated Featue Extaction In the past, most eseach and development in the mobile mapping industy has concentated on the accuacy and eliability of image geoefeencing. As the technology is becoming moe widespead in its use, and the industy expands, this concentation is shifting to efficiency and cost effectiveness. Mobile mapping systems ae designed with many featues to make data analysis and extaction a simple and efficient pocess; howeve, manual extaction inescapably equies a high level of use manipulation and input. To addess maket demands fo effective and economical systems, Geo-3D has focused on automated solutions using lase technology.

Sign Detection tool. Of the 416 signs, a subset of 181 signs was used to detemine the pecision, detection ates and the actual time to make the measuements. Veification of the sign, its position, measuements and the assignment of signcodes took 45 minutes fo the 181 signs in the subset. As Figue 9 displays, Geo-3D s automated technology uses a faction of the time that manual extaction equies, while still maintaining high levels of accuacy and pecision. COMPARISON CRITERIA MANUAL AUTOMATIC Figue 7. Two lase configuations fo automation Duing data acquisition, a two-dimensional lase scanne is mounted on the suvey vehicle (Figue 7. As the vehicle pogesses down the oad, a beam of light is emitted and eflected back to the lase once it has come into contact with objects. This data povides a multitude of infomation that can be used fo detection, geogaphic positioning, measuements and ecognition. 4. APPLICATIONS FOR AUTOMATION 4.1 Road Sign Detection and Recognition Automated oad sign detection is achieved though the use of a pluality of customisable filtes in the Tident-3D Analyst softwae, which distinguish signs fom thei suounding envionment. Once this has been accomplished, geogaphic coodinates ae assigned to the sign s position, and height and width measuements made. The lase also has the ability to measue eflectivity, an extemely impotant chaacteistic of sign visibility. Time to Detect, Locate & Measue 12 sec/sign 15 sec/sign Detection Rate 1% 99% False Detection % 9% Location Pecision Sub-Mete Sub-Mete Figue 9. Compaison of manual and automated data extaction methods in an uban envionment 4.2 Measuing Hoizontal Coss-Slope The obsevations of distance, angle and intensity paametes that ae geneated by the lase s point cloud can be used to geneate a dense and pecise gid of thee-dimensional points. Geo-3D has developed a softwae tool that can automatically geneate oad pofiles (coss sections, using this gid. As illustated in Figue 1, the oad pofiles can be poduced at a defined fequency. Figue 1. Road pofile at fequency of 2 metes Once the pofile has been automatically geneated, it is possible to extact stategically located points in ode to calculate slopes, one between each pai of points. This allows the oad pofile and slopes to be saved in two diffeent data layes that may then be impoted to, and expoted fom, Tident-3D Analyst softwae. Figue 8. Road Sign Recognition softwae Road sign ecognition occus when an asset that has been located, eithe manually o automatically, is matched to a template of images fom a database. This is a semi-automatic pocess that utilizes sign libaies, such as the Manual on Unifom Taffic Contol Devices (MUTCD fom the U.S.A. As this technology is semi-automatic, it gives the use the oppotunity to pefom quality contol and assuance, while geatly educing the time equied to identify a sign (Figue 8. A pilot poject was conducted in Québec, Canada to evaluate the pecision, timing, detection and accuacy ates of the automated technology vesus manual asset extaction. A 37.9 km section of oad was initially used, whee 416 signs wee detected, geogaphically positioned and measued fo height and width in just 9 seconds using the Automated Road This softwae tool is still in the pototype phase; howeve, the esults obtained thus fa ae vey pomising. The automated method was compaed to a taditional method using a fou-foot level ove a distance of 1 metes, with individual sections being measued at intevals of 1 metes. The esults obtained ae compaable and simila. The aveage pecentage of diffeence between the slope measuements taken with the lase vesus the taditional method using a fou-foot level was found to be.7 fo the edge of the left lane and.9 at the cente of the lane. The ight lane had an aveage diffeence of.44 at the cente of the lane and.81 at the edge. The standad deviation anged between.81% and 1.45%. The lage numbe of points poduced by the lase solution and the possibility of geneating pofiles at a highe fequency illustate the efficiency, accuacy and the significant potential of this solution.

4.4 Othe Applications fo Automation Innumeable possibilities exist fo applications of automated technology. The tools that have aleady been developed lend themselves to a vaiety of uses; such as the Hoizontal Coss Slope solution can also be used fo shoulde and ditch pofiling. Othe possible applications include cub height measuement and pavement making detection. The lase can also be used to calculate the vetical cleaance of the oad; assets such as ovehead wies can be clealy identified in the lase s point cloud, as shown in Figue 11. Lases with highe accuacy levels would allow fo detection of even moe specific featues of the oad and the assets found alongside it. Laflamme, C., Kingston T., McCuaig, R., 26. Automated Mobile Mapping fo Asset Manages. XXIII Intenational FIG Congess, Munich, 8-13 Octobe. Schezinge, B. M., 23. Pecise Robust Positioning with Inetial / GPS RTK. ION-GPS Slama, C., 198. Manual of Photogammety, 4 th edition, Ameican Society of Photogammety, Fall Chuch, Viginia, USA. Figue 11. Lase point cloud (left and image (ight showing ovehead wies using Tident-3D Analyst 5. CONCLUDING REMARKS Mobile mapping systems pesent an exciting altenative to taditional methods fo the collection, analysis and extaction of oadside inventoy data fo a vaiety of applications. Systems such as Tident-3D ae being inceasingly used in the fields of tanspotation, municipal and civil engineeing, utilities such as electical distibution and telecommunications, and fo public woks. Futhemoe, multiple depatments in a single oganization have the ability to use the same geoefeenced imagey fo thei specific needs. The integation of lases and automated technologies exponentially deceases the time and economic esouces necessay fo an infastuctue inventoy. This technology pesents the oppotunity to use mobile mapping fo the data collection of elements that have peviously only been collected using taditional methods, such as ovehead cleaance. Advances such as these demonstate that mobile mapping is the oad to the futue fo infastuctue inventoy and maintenance. REFERENCES Gikas, V. and Daskalakis, S., 25. Railway Alignment Computation Using Dual Fequency GPS Data, 2 nd Intenational Confeence on Railway Tanspots Development, Athens, Geece, Vol. 1. Laflamme, C., Loange, J., Laouche, C., Silva, A., Dion, J., 24. Inventaie d infastuctues en abod de outes : une appoche de télémétie mobile efficace et sécuitaie. Géomatique, 3(5, pp. 5-9.