DTM CROSS VALIDATION AND MERGING: PROBLEMS AND SOLUTIONS FOR A CASE STUDY WITHIN THE HELI-DEM PROJECT

Abstract

Almost all official national cartographic bases in Europe include Digital Terrain Models (DTMs). To perform analyses at the borders between countries, transnational geographic information is needed: a transnational DTM can be obtained by merging regional DTMs (usually at low resolution) and other typically local high resolution DTMs. To be used the different DTMs must be in the same three dimensional reference frame, they must not present biases and must be consistent at the nominal scale. The following preliminary actions are required: • 3D reference frame transformation of gridded data, • cross-validation of the regional DTMs, • cross-check of the regional LR DTMs and the local HR DTMs. The paper discusses the study, the implementation and the application of algorithms to solve these problems in the Alpine area between Italy and Switzerland. For this case study, the regional DTMs of Lombardy, Piedmont and Switzerland, respectively with a planimetric resolution of 20, 50 and 25 meters are available. In addition, a LiDAR DTM with a planimetric resolution of 1 meter for the Lombardy and Piedmont hydrographic basins is available. The different DTMs have been transformed to the same reference frame by applying the official national 3D transformations. The cross-validation and the cross-check of the elevation datasets have been performed. All these operations have required the implementation of novel approaches to interpolate and compare DTMs and to spatially analyze their differences.