USING A THREE DIMENSIONAL SPATIAL DATABASE TO ORTHORECTIFY AUTOMATICALLY REMOTE SENSING IMAGES

Following SPOT5 launch, Spot Image and French National Geographic Institute (IGN) have decided to design a worldwide accurate database called Reference3D™ using data from the High Resolution Stereoscopic SPOT5 instrument (HRS). This database consists in three information layers : Digital Elevation Model at 1 arc.second resolution, Orthoimage at 1/6th arc.second resolution and Quality Masks ; with a specification of circular planimetric accuracy better than 16 m for 90 % of the points and elevation accuracy better than 10 m for 90% of the points. It has also been decided to develop and commercialize a system called ANDORRE to archive Reference3D database and produce orthorectified images and DEM thanks to Reference3D™ data. ANDORRE has been designed to take advantage of Reference3D horizontal and altimetric accuracy to automatically register and rectify any image from SPOT satellites in any area where Reference3D™ data is available. This system could also be upgraded to process other satellite data. Spot Image has delegated to French Space Agency (CNES) the realization and industrialization of the algorithmic core of the processing chain. This paper presents the automatic ortho-rectification process composed of three main steps : generation of a reference image (in focal plane geometry) using SPOT rigorous sensor model and Reference3D™ Orthoimage and DEM layers ; modeling of the mis-registration between the reference image and the SPOT image to be processed, using a multiresolution image matching algorithm, in order to improve the SPOT location model;resampling of the image into a cartographic reference frame using Reference3D™ DEM and the improved SPOT location model.It also focuses on some difficult cases and the robustness of the algorithm (different landscapes, DEM and image resolution) and on the processing time needed to achieve the rectification of the SPOT image in different cases.