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build a DEM over wide areas where elevation data from non-homogeneous (in density and accuracy) input sources
are available. The input elevation data include contour lines and spot heights derived from the Italian Regional topographic
maps, satellite-based global positioning system points, ground based and radar altimetry data. Owing to the
great heterogeneity of the input data density, the DEM format that better preserves the original accuracy is a Triangular
Irregular Network (TIN). A Delaunay-based TIN structure is improved by using the DEST algorithm that enhances
input data by evaluating inferred break-lines. Accordingly to this approach, biased distributions in slopes and
elevations are absent. To prevent discontinuities at the boundary between regions characterized by data with different
resolution a cubic Hermite blending weight S-shaped function is adopted. The TIN of Italy consists of 1.39×109
triangles. The average triangle area ranges from 12 to about 13000 m2 accordingly to different morphologies and different
sources. About 50% of the model has a local average triangle area <500 m2. The vertical accuracy of the obtained
DEM is evaluated by more than 200000 sparse control points. The overall Root Mean Square Error (RMSE)
is less than 3.5 m. The obtained national-scale DEM constitutes an useful support to carry out accurate geomorphological
and geological investigations over large areas. The problem of choosing the best step size in deriving a grid
from a TIN is then discussed and a method to quantify the loss of vertical information is presented as a function of
the grid step. Some examples of DEM application are outlined. Under request, an high resolution stereo image database
of the whole Italian territory (derived from the presented DEM) is available to browse via internet.
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