How to rasterize walls for grid calculations

For some calculations, it may be relevant to know where the walls of structures exist. This is a trivial consideration, but a bit more complex to implement in a geographical calculation. However, by using some localized checks on the behavior and local changes of elevation models, it is possible to create a spatial calculation which can find the locations of walls of structures.

Editor → Current Situation (Ribbon tab) → Overlays (Ribbon bar)

How to rasterize walls for grid calculations:

1. Add a Heightmap Overlay, configured as DTM, to the Project (if it does not exist yet)
2. Add a Heightmap Overlay, configured as DSM, to the Project (if it does not exist yet)
3. Add an Average Overlay to the Project.
   Set the averaging to the DSM Heightmap Overlay.
   Set the averaging distance to approximately 2.5 times the grid cell size.
4. Add a Combo Overlay to the Project with the following configuration:
   A: DTM Overlay
   B:DSM Overlay
   C:Average Overlay of DSM
   Formula: AND(GT(SUB(C, A), 1), GT(SUB(C, B), 1))
5. Modify the legend of the Combo Overlay to have only the following values:
   Value 0: No wall
   Value 1: Wall
6. Rename the Combo Overlay to "Walls"

Notes

• This calculations performs an estimation of the locations of walls, and may miss spots. This calculation should therefor not be taken at absolute value, but can be used as a valid estimation in other calculations, such as the percentage of walls which also overlaps with specific sightlines.
• The formula of the Combo Overlay checks whether the localized average DSM exceeds the absolute height by at least 1 meter, which generally means that the height of a wall should be at least 2 meters high. By changing the "1" into a lower or higher number, the approximation can be made more or less sensitive respectively.