DTM and DSM Creation

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There is no official usage of the Term Digital Terrain Model (DTM) and Digital Surface Model (DSM). In most cases, the first term represents the bare ground surface while the second term represents the Earth’s surface including all objects on it. The term Digital Elevation Model (DEM) represents every elevation information.
Map uses elevation models, either for direct production or ortho-correction of orthophotos and true orthophotos. For the creation of elevation models, the company uses airborne and terrestrial Lidar scanners which extract elevation information with the best accuracy and density possible as well as stereoscopic aerial images. Map has already created a DTM for the total of the Greek surface from which any new elevation information can be extracted.
The initial DTM for the whole country’s surface was created with the use of overlapped Aster Satellite Images. Combined with known geodetic points and the digitizing of rivers and triangulation points, this DTM has been certified with accuracy better than 10m, exceeding the specifications of the 1:50.000 scale (pixel size 40cm). Moreover, this product has been updated with stereo aerial images processing (scales from 1:40.000 to 1:15.000). As a result, a DTM of accuracy better than 3m (grid size 20m) of the total of the Greek surface is offered.