To the Graduate Council: I am submitting herewith a thesis written by ...

Chapter 3: Data Collection and Modeling 263 DATA COLLECTION ANDMODELINGThe computer vision approach to reverse engineering and under vehicle inspectionrequires digitized data. We hence require a system that can automatically (or withminimal manual intervention) capture geometric structure of an object and store thesubsequent shape and topology information as a digitized model. We make use of 3Drange scanners for this task. We introduce in this chapter the process of range dataacquisition and solid modeling geared towards generating mesh models using a sheetof-lightlaser scanning mechanism and share our experience with the IVP range sensorto create 3D models of automotive parts and automotive scenes.3.1 Range Data AcquisitionRange images are a special class of digital images. Each pixel of a range imageexpresses the distance between a known reference frame and a visible point in thescene. Therefore, a range image produces the 3D structure (though not completely) ofa scene and can be best understood as a sampled surface in 3D. Range images (oftenreferred as depth maps, depth images, xyz maps, surface profiles and 2.5D images) areobtained using range sensors. Range sensors are devices that make use of opticalphenomena to measure range. In general range image acquisition systems areclassified into one of the following types based on their principle of operation:triangulation (passive or active), time of flight, focusing, holography and diffraction.We discuss each of these methods very briefly in Section 3.1.1 and document theprinciple of operation and calibration details of our range sensor in Section 3.1.2.3.1.1 Range Acquisition SystemsWe begin our discussion with triangulation-based techniques. Passive triangulation(stereo) is the way humans perceive depth. It involves two cameras taking a picture ofthe same scene from two different locations at the same instant of time. Depth cues areextracted by matching correspondences in the two images and using epipolargeometry. Passive triangulation is however challenged by the ill-posed problem ofcorrespondence in stereo matching. The correspondence problem is eliminated by