Thirdly, applications using DTMs are now part of our everyday lives (e.g., Google Earth 3, Microsoft Virtual Earth 4, NASA World Wind 5, Radrouten Planer 6…). These additional data sources can provide valuable input for integrated DTM production, as exemplified in Slovenia (Podobnikar, 2005) and in Europe (EuroGeographics, 2008). Even datasets without height attributes such as lines of a hydrological network, roads, railways, and standing water polygons can be used (Podobnikar, 2005). In addition to the aerial photographs and contour lines, different point datasets with height attributes could also be applied, such as fundamental geodetic network points, boundary points of land-cadastre, databases of buildings, spot elevations, and other related datasets such as highway construction or hydrological network measurements. The second factor is the increasing availability of additional data sources that are useful for the DTM quality assessment or enhancement. For larger scales and more local usage, airborne laser scanning (ALS) techniques have been applied 2 (e.g. At small scales (coarser spatial resolution) radar interferometric techniques (IfSAR) had been applied to generate global DTMs 1 (Burrough and McDonnell, 1998 Maune, 2001). The first was the introduction and development of new methods for data acquisition, especially from satellites and airplanes.