DIGITAL SURFACE MODELS IN BUILD UP AREAS BASED ON VERY HIGH RESOLUTION SPACE IMAGES

The geometric resolution of very high resolution optical space sensors like IKONOS, QuickBird and OrbView-3 allows the generation of detailed digital surface models also in build up areas. This may be used as base for a 3D-city model. As result of automatic image matching the height value of the building top show the form of the houses within the spacing of the height models well, but in most cases the neighboured points on the ground have some distance from the building caused by viewing shadows. The size of the used sub-matrix for image matching also will lead to some rounding of the edges caused by the fact that the pixels partially are located on top of the buildings and partially on the ground or even the wall. IKONOS, QuickBird, OrbView-3 and Cartosat-1 stereo pairs have been used for the generation of digital surface models in city areas. By simple theory the height accuracy is linear depending upon the height-to-base-ratio. This is the case for open and flat areas as well as for manual measurement, but not for image matching in cities. With a small height-to-base-relation (close to 1:1) only a limited number of points can be determined on the ground, degrading the overall information contents. In city areas it has been shown that a smaller convergence angle has some advantages and is not linear influencing the vertical accuracy - for a small convergence angle of the space images the standard deviation of the x-parallaxes is still better. Of course the mentioned problems are not the same for the very time consuming manual 3D-measurements. But in some cases of very high buildings also problems of the stereo impression are caused by a large convergence angle of the used satellites. Also this is leading to relative better results for a limited height-to-base-relation.