Automating the checking and correcting of dems without reference data

The need for Digital Elevation Model (DEM) checking has raised since the automated matching techniques emerged. The use of reference data is a luxury and therefore cannot be used in all cases. This article presents a completely new mathematical model, which translates discrepancies between two orthophotographs created from different photographs, into precise corrections of the DEM. These corrections are the differences from the real surface and, if applied over the existing DEM, can produce a more accurate one. The mathematical model is straightforward, does not approximate, and therefore there is no need for iterations. In order to test the algorithm a reference DEM has been manually collected and distorted with a known pattern. The corrections produced by the algorithm follow the known pattern. Tests over automatically created DEMs by commercial software has also been made and compared against the reference DTM. Obvious applications include checking of automatically created DEMs, refinement of existing DEMs using aerial photographs and update of orthophotographs based on the previous DEM and new imagery