Abstract
Digital stereo-photogrammetry allows users an automatic evaluation of the spatial dimension and the surface texture of objects. The integration of image analysis techniques simplifies the automation of evaluation of large image sets and offers a high accuracy [1]. Due to the substantial similarities of stereoscopic image pairs, correlation techniques provide measurements of subpixel precision for corresponding image points. With the help of an automated point search algorithm in image sets identical points are used to associate pairs of images to stereo models and group them. The found identical points in all images are basis for calculation of the relative orientation of each stereo model as well as defining the relation of neighboured stereo models. By using proper filter strategies incorrect points are removed and the relative orientation of the stereo model can be made automatically. With the help of 3D-reference points or distances at the object or a defined distance of camera basis the stereo model is orientated absolute. An adapted expansion- and matching algorithm offers the possibility to scan the object surface automatically. The result is a three dimensional point cloud; the scan resolution depends on image quality. With the integration of the iterative closest point- algorithm (ICP) these partial point clouds are fitted to a total point cloud. In this way, 3D-reference points are not necessary. With the help of the implemented triangulation algorithm a digital surface models (DSM) can be created. The texturing can be made automatically by the usage of the images that were used for scanning the object surface. It is possible to texture the surface model directly or to generate orthophotos automatically. By using of calibrated digital SLR cameras with full frame sensor a high accuracy can be reached. A big advantage is the possibility to control the accuracy and quality of the 3d-objectdocumentation with the resolution of the images. The procedure described here is implemented in software Metigo 3D.
Highlights
Two digital reflex cameras Canon EOS 5D Mark II were used for 3D-evaluation on the base of stereo models in an image set at the shown object (Castle of Katzenstein)
With the integration of the iterative closest point- algorithm (ICP) these partial point clouds are fitted to a total point cloud
The here shown east wall with apse was covered with 13 stereo models and round about 100 reference points were measured by a tacheometer
Summary
Two digital reflex cameras Canon EOS 5D Mark II were used for 3D-evaluation on the base of stereo models in an image set at the shown object (Castle of Katzenstein). The calculation of relative orientation of both images of the stereo model is made on the base of the known control points. If there are not enough control points for model orientation, additional image coordinates could be detected automatically or measured by hand. By additional measurement of reference points the absolute orientation of one stereo model into overall coordinate system is made. In the absence or insufficient relation of the stereo models, additional reference points on the object surface can be measured and the absolute orientation can be calculated manually
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