Where can I find documentation on the tool Relief Segmentation of the library Terrain Analysis?
Relief Segmentation is one of SAGA Tool Chain, like Model Builder / Graphical Modeler in other GIS software. So it does not have any official documentation, as you have already found out. Still, it works closely with SAGA as if it were a native SAGA Tools.
This is a short summary of Relief Segmentation.
- Elevation (DEM) raster data (projected to CRS in meters)
Position Index Radius: You will need to provide Inner radius (m); Outer radius (m) pair. This is used in TPI calculation.
Band width: Default is set to 2. I would suggest a larger number (e.g. 5). It will reduce the number of seed points, thus slightly increase the size of polygons. Usually larger polygons are easier for our visual check. Also, it will run faster (in my environment turn-around time with Band width=5 was approx. 40% shorter than Band width=2).
Number of Clusters: Default is 10 and it would be sufficient.
[Basic Workflow of the tool] - All these process are automatically done by the tool.
- Calculate Topographic Openness, Slope, TPI, and TWI.
- Perform Principle Component Analysis (PCA)
- Generate Seed points from PCA output.
- Create polygons (simple region growing algorithm)
- Vectorize polygons and calculate statistics
- Cluster Analysis on the output from 5.
- Dissolve polygons.
- The output polygon has only one attribute = Cluster Number. It is up to the user to understand how these polygons are related to the original topography.