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Poster Session
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A Topographic contour lines reading system
Geometric processing
- Conversion of Rater to Vector
Line following is carried out in raster data structure overlapping the original image. The raster data are converted into vector form to be easy to geometric rectification and plotting.
- Geometric Rectification
Because the following reasons, geometric rectification should be done for the results of contour of line following.
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The orientation of the CCD camera is unknown. That will be solved by using 4 grid (e.g. kilometer grids) points as control points.
- Geometric distortion of CCD camera needs to be corrected, which can be together with the geometric rectification.
- Mosaicking
Because of the limited size of CCD array, a map sheet needs to be imaged patch by patch to obtain a satisfactory resolution. Therefore the rectified data should be mosaicked from patchs. To simplify the procedure, kilometer grids are used as the patch edges. All patchs are rectified into a common co-ordinate system.
Experiment and conclusion
A normal pointed topographic map has been chosen for the experiment. A patch of the results is shown in Fog. 5 in which the detected lines are completed overlapping on the original contour lines. The maximum deviation is less than 0.1mm, because the pixel is 0.2mm. The results can be displayed in both raster and vector form. Fig.6 is a Raster displaying.
Fig.5 Overlap display
Fig.6 Contour lines
References
- T. Luhman etc. Proceeding on fast processing of photogrammetric data, ISPRS (1987) 35.
- Y. Shirai, Three dimensional computer vision, Springer verlag (1987) 32
- Lin Zongjian, Acta Geodetica et Cartogra-Phica Sinica, 14-2 (1985) 111
- Lin Zongjian, Journal of Wuhan Technical university o surveying and Mapping 13-4 (1988) 37
- Wang Zhizhuo, Principles of Photogrammetry, Publishing House of Surveying and Mapping Beijing.
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