TRUEDOP – A NEW QUALITY STEP FOR OFFICIAL ORTHOPHOTOS

Abstract. The National Mapping Agencies (NMA) of the German federal states derive nationwide digital orthophotos with a ground resolution of 10 to 20 cm by aerial surveys at regular cycles of two or three years. Standard surveys use large format cameras, the direct georeferencing informations and normal overlap ratios of 70% forward and 30% sideward overlap. These basic geodatasets are in use in a variety of applications. Most commonly authoritive agencies use these orthophotos as a fundamental dataset in their GIS-systems.

Interactive work for deriving the orthopohotos is necessary for updating the terrain model and for defining seamlines for objects above the reference plane. With respect to the developments in dense image matching using the semi global matching algorithms it is possible to derive surface models with pixel resolution and full color informations of the aerial photos. Using these high resolutioned height informations for the orthophoto procedure some software solutions are able to derive the quality of true orthophotos without remaining occluded areas. The rectification additionally uses always a height model from the same survey so that there will be no interactive steps in the working process left. TrueDOP visualises the correct position of all objects without the fault effect of the central perspective. This is a basic condition for using the dataset for effective rasterbased classification applications, in special for the use in change detection.

The Working Committee of the Surveying Authorities of the States of the Federal Republic Germany (AdV) evaluates the replacement of the classical ATKIS-DOP by the TrueDOP. In this connection the TrueDOP is understood as a qualitative upgrading of the existing AdV-product ATKIS-DOP. The resulting advantages and disadvantages in reference to the technical and economical aspects are considered and compared.