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Fig. 14.1 Base of
inaccuracies arising from a
different 2D-3D relief
expression (source: the
authors)
models. A map is the most frequent source of altimetric relationships used for
determining values for computer models. Projection of the earth's surface to a topo-
graphic
projection plane causes the biggest deviations in relief expression. In the case
where the region is used as one of the input quantities, a difference in 2D and 3D
area appears (Fig. 14.1).
Selection of type of digital elevation model : When generating a DEM the selec-
tion of type (grid, TIN) entails another deviation from the reality - the modelled
earth surface is represented either by a system of blocks (raster grid type) or an
irregular polyhedron (vector TIN type). It is generally true that the TIN type is
a much more accurate relief expression than the grid type; nevertheless its struc-
ture does not necessarily have to be suitable as the input for all models of physical
geographic phenomena.
Selection of interpolation method of DEM : Even when the most suitable alti-
metric data source is selected, a DEM of the highest accuracy is not necessarily
ensured because to generate the model it is necessary to choose a suitable interpo-
lation method, and set its parameters. The selection of an interpolation method and
its parameters depends primarily on the relief type. The dependencies of setting the
parameters of interpolation methods and the relief types are discussed in the work
by Kadlcíková and Tucek (2008).
The generated DEM is used for deriving values of various morphometric and
other characteristics of relief (Voženílek et al., 2001); however, their values differ
according to the parameters of interpolation methods used. An improperly selected
and set interpolation method results in the creation of a DEM of low quality, which
then results in the derivation of erroneous values of geomorphometric parameters.
Thanks to DEM visualisation, the following Fig. 14.2 shows changes in the course
of the relief (and derived morphometric characteristics) depending on the changing
values of input parameters of interpolation methods.
Errors in derived parameters are usually much more evident than in the original
DEMs. This is further enhanced by the properties (configuration) of the real relief -
flat land, hilly areas, highlands and mountainous areas. It is evident that there is
direct proportion between the relative relief segmentation and the examined inaccu-
racies - in hilly areas the inaccuracies are smaller than in mountainous areas (see
previous text in this chapter). Any error in the DEM then generates an error in the
application results where relief is one of the factors.
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