DEM optimization

Algorithm

With the DEM optimization operation, the following can be achieved:

Gradual drop of (drainage) segments in the output DEM, over a certain distance to the (drainage) segments.
Gradual raise of (watershed-divide) segments on the output DEM, over a certain distance to the (watershed-divide) segments.
Additional sharp drop or raise of segments on top of the gradual drop or raise.
Simple drop or raise of polygons in the output DEM.

The output Digital Elevation Model (DEM) is calculated based on:

The parameters Buffer distance, Smooth drop and Sharp drop can be specified:

as simple values for all segments, or
in an attribute table of the segment or polygon map for each class/ID of the segments or polygons.

Process:

The height values of the input DEM are read into memory (OriginalHeight).
The vector map with the drainage or catchment features is temporarily rasterized.
For each pixel in the DEM, distances are calculated towards the closest drainage/catchment feature.
Thus, for each pixel the distance towards the nearest drainage/catchment feature is known (CalcDist).

In case an attribute table is used, also a temporary Thiessen map is calculated, so that for each pixel in the DEM it is known which BufferDistance, SmoothDrop and SharpDrop values should be used.

NewTempHeight = OriginalHeight - SmoothDrop * (BufferDistance - CalcDist) / BufferDistance

NewTempHeight = OriginalHeight

NewTempHeight = NewTempHeight - SharpDrop

Reference:

The DEM optimization operation complies with the AGREE method, developed by Ferdi Hellweger at the University of Texas, Austin, 1997. For more information, refer to: http://www.ce.utexas.edu/prof/maidment/gishydro/ferdi/research/agree/agree.html