Extraction of 3D data by several methods for the building of a 3D model in ARCGIS: Laser Scanning, direct laser rangefinder measurements and Pictometry. Akingbade A. Akinfenwa
12/01/05
Introduction
This paper explores the use of 3D Riegl laser scanners to capture information from a building and the extraction of relevant information for use in GIS. Further more, a comparison was made from the result in using laser advantage scanner and pictometry software to see the advantages of each of these methods for extraction.
The use of 3D laser scanners is becoming more popular by the day. Their applications are diverse in nature. This includes use in Archeology site to have data preserved and analyzed for later use, Architecture use includes extraction of floor plans and dimension of different structures, Land surveying and Civil engineers find it extremely useful for leveling and traversing of different projects. In this project, I explored the use of 3D laser scanner for use in GIS software and the possibilities in extraction of information for use in GIS.
Problem Statement/Project Objective
The purpose of this project is to explore the possibility of using information got from 3Dlaser-scanned data in GIS Software. How can the data be effectively used? What are the advantages of using the methods? What are the demerits of it use? What are the accuracy issues? Which method is better over which when comparing with Laser advantage and Pictometry? The project shows how the extraction is carried out from the beginning and how the extracted information is used for analysis in GIS. A comparison of information obtained from Footprint done using Total station and extracted data from laser scanned data is also shown.
Literature Review
In the past, the numerous challenges of 3-D modeling in Photorealistic GIS were a thing of great concern. However, in recent years the advent of Terrestrial Laser scanner revolutionized the creation of photorealistic 3D-GIS models. The big concern of Geometric accuracy and the problems of handling areas that weren’t smooth such as over hang cliff was a big challenge for 3-D GIS tools. The use of the new Terrestrial laser scanner technology is gradually integrating into virtually every phase of life. It integration with High accurate GPS Satellite units and digital camera makes it much appealing because it gives you it point cloud data’s in real time.
The laser scanner measures several thousand points per second, thus data acquisition for a single position is finished after only a few minutes. Through a number of scanned performed on locations chosen around an object of interest, even niches, windows can be registered. (Christian et al.,2004)
The 3D laser scanner is an active remote sensing because no additional personnel’s are needed to hold a range of pole or to place targets for measuring surfaces. (P:20) Combining a pulsed laser with high-speed scanning optics, an accurate 3D model is achievable.
Terrestrial laser scanning technology can be used to efficiently and cost effectively creates 3D models and drawings. Construction and Architectural design has been a focus for many laser application developments for the purpose of maintenance and reconstruction. However, this technology as been proven to be successful to develop retrofit design , create faster, safer, and more complete topographic and engineering surveys; and provide for more efficient operations and maintenances. The technology is can also be used for virtual reality applications.
The 3D modeling in Terrestrial laser scanning process involves the following primary steps: Target the area of structure, scan the area or structure and create a point cloud, color the points, “shrink wrap” the surface in the field, register the scans together and create a virtual database and finally create the detailed 3D model (Edward et al.,2001)
The numerous applications of 3D Terrestrial laser scanner make it a great use for many applications. The 3D models created through laser scanning include extensive detail and allow for ultra-fast measuring. If desired, two-dimensional drawings can be created from 3D models. The area of construction design is one of the largest areas for 3D modeling development. The application includes roadway, bridge and building and rehabilitation. The benefits in design construction projects using 3D modeling includes: coordination issues can be minimize using virtual design and construction, 3D modeling provides efficient generation of multiple views, 3D modeling can generate automatic bill of materials, the data generated through laser scanning and modeling cab be efficiently integrated into analysis software. (Edward et al.,2001)
The application in transportation related fields is also huge. It can provides many benefits such as ability to survey during heavy traffic times without positioning surveyors in the roadway and without closing the road, the laser scanning is also a good source of creating as-built drawings of bridges to assist in modifications. This technology also has the potential to perform storm stimulations to evaluate the flooding and ponding effects of current and proposed drainage structures, assessing pot holes, and inspecting roads for rutting. In surveying, when assessibity and safety issues prevent the traditional survey techniques laser scanning is an excellent substitutes. The 3D laser scanning can be used to perform accurate and efficient as-built surveys and before-and-after surveys. In accessible, complex arrangement and hazardous locations can easily be modeled. (Edward et al.,2001)
Other applications include modeling of historic sites for it maintenances, Investigation in accident scenes by police department and planning, logistics and management of existing buildings and creating “what if” scenarios relating to installing new structure and aiding in effective planning for the future.3D modeling could be used to measure and verify quantities of work to be performed. Laser scanning could also be used for quality control (e.g. measuring location f anchor bolts, evaluation of cut and fill, scanning rebar prior to pour. (Edward et al.,2001)
There are several advantages to laser scanning technology. Laser scanning is a non-destructive technique that can be used to map all scales of site recording except for micro-scale.
The laser scanned point cloud can be used to produce very accurate topographic maps on the order of millimeter to decimeter contour intervals.
The scanned data are tied to real world coordinates which makes it possible to be used for GIS or spatial statistical analysis, the point cloud can be viewed in 2.5D(contours and digital elevation model), which permits the viewer see the site in a context that is more closely allied to reality. It reduces the ambiguity associated with interpretation of surfaces feature attributed from a topographic map. Unlike photography, laser scanning does not have distortion associated with the end products and the scanner does not require particular lightning or any lightning (Thad et al.)
With laser scanner systems, capable of working in most real world environments under a variety of conditions, numerous applications have opened up. State of the art, high precision, high speed laser scanners provide accurate and virtual and geometric measurements. To realize surveying task for traffic construction analysis, point clouds, measured by the laser scanner, are transformed into three- dimensional models, describing the environmental geometrically. In addition, the virtual information of the data measured is used to determine surface conditions of the objects, indicating possibilities of cracks and other damages in the structure itself. Geometric constraints like planes, cylinders or meshing techniques may be adapted resulting on a CAD model. (Krestchmer et al.,2004)
The use of VRML (Virtual Reality Modeling Language) as become a widely use tool for visualizing vector graphics on the WWW (World Wide Web). The VRML is an interpreted 3D modeling language introduced as a standard in 1993 and VRML97 a recognized standard (ISO/IEC14772) in 1997. The models created using this language require a VRML browser such as; Cosmo player, corona etc. Most 3D software’s allow importing and exporting into VRML format for their 3D Models.
Data
The University of Texas at Dallas planning unit gave floor plan and footprint for the project, The City of Richardson gave Static images from Pictometry software, Obtained scanned data (3D Riegl laser scanner) from University of Texas at Dallas, Geosciences department. Ground LIDAR data from City of Richardson. The use of ARCGIS 9.0 software, Polyworks, Riscan Pro from University of Texas at Dallas.
Analysis and Methodology
Three-Dimensional Survey with Riegl LMS –z360i
The equipment used for this project was a Riegl 360 z, which allows to measure with extreme speed and accuracy. It is possible to set it field of view to both horizontal and vertical directions (90° x 360°) the range can go as far as 1- 200m using laser class 1.
The building was scanned from four different directions to capture every part of the building. The reason for this is to allow a capture of all the angles before going ahead to do a post-processing of the scanned data. The laser scanner well mounted, on a tripod stand and the scanner allowed continuing capturing information at each point until it done.
Riscan Analysis
The scanned data will now go through a post-processing phase. This is when scanned data is imported into Riscan to see how well each of the scanned images are see figure 1. The next phase was exporting this information into Polyworks software.
Fig 1
Polyworks Analysis
The scanned data is exported into polyworks software, for a more comprehensive analysis. The polyworks generate statistic for alignment before the post-processing takes place. See figure 2. The polyworks software come in modules for completion of project as follow: IMALIGN which allows you to have a view of the scanned image and see how it looks, the IMEDIT allows you to do some editing and analysis, IMMERGE helps you to have a merged model after many auto correction process have taken place, IMINSPECT allows the user to do higher level of precise extraction of measurements, angles, planes, lines, points and other features.
Fig 2
The captured image was the University of Texas at Dallas Theater Building. different angles of the building was captured using the 3D laser The number of measured point for each scanner was over 500000 at a horizontal and vertical resolution of 0.5 for every scan used. In the duration of time used to capture each of the angles, it captured millions of point clouds.
Fig 3
The different module of Polyworks had different functions and the procedure went as follows. The IMALIGN helped to align the four different scanned data for use see figure 4 and 5. The reason was to have a common identifiable point between each of the scanned image to do a referencing to it and have an auto –alignment generated using the software. The IMEDIT helped to do cleaning some of the noise (unwanted data) from the data see figure 6. The IMMERGE helped to do an auto merge based on specified iteration. The IMINSPECT was used to extract information for measurement of specific areas.
Fig 4 Image before align (IMALIGN) fig 5 image after align (IMALIGN)
Fig 6
IMINSPECT Extraction
The use the 3D Polyworks license IMINSPECT allows for the effective measurement and analysis of the data extracted from the building. There is a lot of information that can be extracted from the models. The examples are polylines, vectors, distances, angles, radius, planes, point clouds etc PolyLines /Lines was extracted from the 3D laser scan Model and the extracted information used in Arscene GIS. The extraction using IMINSPECT is shown below in figure 7 and 8.
Fig 7 Extraction of height/width Fig 8 Extraction of polylines
Exporting into GIS Arcscene
The extracted information can be exported as a drawing file (CAD File) imported into GIS Arcscene. Firstly, the model is brought into ArcMap for cleaning, and eventually moved into AcScene .The exported image to ArcMap is shown in fig 9. and noise shown in figure 10
Fig 9 Exported Model in Arc Map Fig 10 ArcMap showing noise
The scanned data is inspected in Arc Map and checked. The created model in Polyworks is imported into Arc Scene to enable a 3D view. The data is so huge and a fast processing speed is needed for the computer to perform well. Arc Scene is used to view the scanned model see figure 11.
Fig 11 Scanned Model viewed in ArcScene
Laser Advantage Fast scanner
The laser advantage scanner is a rugged and lightweight scanner used for quick capture of points and measuring of features with unique software. The laser advantage scanner was used to capture measurement of the width of the building for the front and rear view. With an Accuracy of 10cm, the result is compared with those of the Polyworks extracted result. See Table 1
Pictometry Software
This system combines aerial imaging with a unique software system that has the ability to provide visual data and strong analysis. The software also allows the extraction of measurement vertically, horizontally, bearing, oblique etc.With an accuracy of 2m-6m, The software was used to extract dimension for the theater building and the result compared to the more accurate polyworks software. See Table 1 and graph 1
Results for each method
The obtained reading for each of the methods is shown in the table1 below.
Polyworks / Atlanta Advantage / PictometryTheatre Front View / 34.01 / 33.91 / 37.01
Theatre Side View2 / 40.51 / 40.61 / 37.52
overall height / 8.19 / 8.29 / 11.17
Rooftops / 2.41 / 2.51 / 4.43
Length to Roof Base / 5.11 / 5.01 / 7.22
Table 1
The differences (Using Polyworks Accuracy of 1cm as Reference)
Atlanta Advantage / PictometryTheatre Front View / 0.1 / 3
Theatre Side View2 / -0.1 / 2.99
overall height / -0.1 / 2.98
Rooftops / 0.1 / -2.02
Length to Roof Base / 0.1 / -2.11
Table 2
Graph of Comparison
Graph 1
Conclusion
Scanned data obtained from 3D Fast scanners can be integrated into GIS and