The Digital Elevation Model 1:25.000 (dem 25) for the Federal Republic of Germany

The fusion respectively the homogenisation of the digital terrain models of the federal states (Länder) of Germany to a nationwide digital elevation model for Germany is described. The aim is a nationwide, consistent, at the moment not yet existing, digital elevation model with an accuracy of ±1 to ±3 m. The incoming data from the states have different grid sizes, techniques and dates of data acquisition and, of course, different accuracies. These different accuracies range from the quality of laser scanning or high resolution photogrammetry to the quality of digitalisation of contour lines. For checking the quality of each incoming database the differences in the overlapping areas adjoining the neighbour state are calculated. Regions showing great differences (errors) are checked by field measurements using a DGPS-method (SAPOS). After checking the data the error-free DTM-Data will be merged with algorithms that depend on the data accuracy. Possible height steps in the data will be prevented using a distance-depending adaptation. After the flooding catastrophe of the river „Elbe“ in the year 2002 Germany has an urgent demand for high resolution digital elevation models with respects to possible flooding areas. Therefore, the DEM25 will be supplemented with a high resolution DEM with an accuracy of 0,5 m and better in these regions.