DEM Terrain Attributes
Category: Mega-Polis → Analysis → Analysis Design Tools
Node ID:SvMegapolisDemTerrainAttributes
Tooltip: Provides methods for extract Terrain Attributes values: Aspect, Curvature, and Slope.
Dependencies:richdem
Functionality
Computes a selected terrain attribute from a DEM raster array using RichDEM (rd.TerrainAttribute).
It accepts a DEM array (2D elevation grid), converts it into a RichDEM rdarray with a fixed NoData value, then calculates one attribute (e.g., slope in degrees, aspect, curvature) and outputs:
- A flattened 1D array of attribute values
- The full attribute array (same shape as the input DEM)
Inputs
| Socket | Type | Description |
|---|---|---|
| Dem Array | SvStringsSocket | 2D DEM elevation array (e.g., output from Read DEM). Must be linked. |
Parameters
| Name | Type | Default | Description |
|---|---|---|---|
Terrain Attribute (attributetype) |
Enum | slope_degrees |
Select which attribute RichDEM computes via rd.TerrainAttribute(..., attrib=...). |
Available attributes
aspect
profile_curvature
planform_curvature
curvature
slope_riserun
slope_degrees
slope_percentage
slope_radians
Outputs
| Socket | Type | Description |
|---|---|---|
| Attribute Values | SvVerticesSocket | Flattened 1D array of computed attribute values (dem_slope.flatten()). |
| Array Out | SvVerticesSocket | Full 2D attribute array (dem_slope) as returned by RichDEM. |
Example
Compute slope (degrees) from a DEM
- Use Read DEM to load a GeoTIFF and output the elevation matrix (DEM array).
- Connect Read DEM → DEM data (array) into Dem Array.
- In Terrain Attribute, select
slope_degrees. - Use outputs:
- Attribute Values to drive point-based mapping (e.g., colour/size by slope)
- Array Out for raster-style workflows or further terrain processing
Compute aspect
- Set Terrain Attribute to
aspect. - Visualise Attribute Values as a histogram or map values back onto the terrain grid.
Notes
- The node wraps the input array as
rd.rdarray(self.array, no_data=-9999). If your DEM uses a different NoData value, you may want to standardise it upstream. - Output Attribute Values is a flattened 1D array. If you need grid indexing, use Array Out (2D).