Aspects on True-Orthophoto Production

In many occasions orthophotos in the background of GIS applications enrich their presentation. Often they serve for data capturing. Geometrically such images posses a defined, homogeneous geometry. One produces orthophotos since several decades with ever increasing demands and performance in quality and quantity. However, large-scale city orthophotos using standard algorithms and procedures typically have following problems: (a) Displacements and occlusions make it difficult to superimpose vector data for checking and change detection purposes; (b) The orthorectification of the image is partly geometrically inaccurate and/or incomplete (i.e., buildings are distorted from their true location as they are not modelled in the DTM). By using Digital Surface Models (DSM) and considering occluded areas it is possible to generate True-Orthophotos which do not have above mentioned problems. In this article the aspects on the generation of True-Orthophotos will be discussed. Different methods and economical aspects to build up the DSM for the True-Orthophoto production will be mentioned.