Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 18

Application requirements play an important role to expected characteristics of
the used DEM. For example, it is not necessary to use high geomorphologic
quality of DEM for regional, small-scale analysis and for calculating average
altitudes. But geomorphologic accuracy is more sensitive for visibility analyses
and even more for analyses that uses algorithms bases on derivates like slope,
aspect, cost surface, drainage, path simulation, and so on [ 15 ].
Interpolation techniques based on the principles of spatial autocorrelation,
which assumes that objects close together are more similar than objects far apart.
On the edges of the interpolated area extrapolation is also reasonable. Unfortu-
nately, no one of the interpolation techniques is universal for all data sources,
geomorphologic phenomenon or other purposes. It is necessary to be aware that in
the praxis, different interpolation methods and interpolation parameters on the
same data sources lead to different results. The best chosen algorithms on fair data
sources should not differentiate much from nominal ground, that is idealization of
our desired model and which is commonly similar to the actual Earth's surface.
Divergences between results of interpolation and from nominal ground are espe-
cially consequences of the following circumstances [ 15 ]:
• Available data sources do not approximate terrain distribution, density, accu-
racy, etc., of the sources is not appropriate.
• Selected interpolation algorithm is labile (is not robust enough) on the employed
data sources.
• Chosen, interpolation algorithms or data structure, are not suitable for selected
terrain geomorphology or application.
• Perception or interpretation of the Earth's surface (better: nominal ground) is
not the same when more DEM operators work on the same problem; operator's
own imagination is common and a reasonable problem in DEM production [ 15 ].
Application requirements play an important role to expected characteristics of
the used DEM. For example, it is not needed high geomorphologic quality of DEM
for regional, small-scale analysis and for calculating average altitudes. But geo-
morphologic and hydraulic accuracy is more sensitive for visibility analyses and
even more for analyses that uses algorithms bases on derivates like slope, aspect,
cost surface, drainage, path simulation, bathymetry of the river, and so on [ 15 ].
In the most cases, a very high quality DEM should cover all application
demands. So it is preferable to find a good and robust interpolation algorithm.
Even if a more generalized surface is required, DEM with high detail can be
simplified to the required quality. It should be noticed that appropriate general-
ization methods are very important for producing required DEM. Commonly these
methods are complex [ 15 ].
The quality of a derived DEM can vary greatly depending on the data source
and the interpolation technique. The desired quality depends on the application for
which the DEM is to be used, but a DEM created for one application is often used
for other purposes.