Topographic Position Index
Each cell's elevation minus the mean of its eight neighbours; positive on ridges, negative in valleys.
Pitfall. Some tools compute it over a larger window or standardise it by the window's standard deviation, which is a different number.
Pitfall. Cells on the raster's edge have incomplete neighbourhoods; engines leave them nodata or compute them differently.
| Also called | TPI, difference from mean elevation, gdaldem TPI |
|---|---|
| Group | raster/terrain |
| Checks | raster.nodata |
| Pitfalls | 2 listed above |
| Columbus tool | Not stated |
| Notes | Not stated |
| Status | active |
| Broader | Not stated |
| Narrower | Not stated |
| Related |
Parameters
Not stated
Inputs and outputs
| Direction | Name | Type | Geometry | Note |
|---|---|---|---|---|
| Input | raster | raster | Not stated | An elevation model. |
| Output | output | raster | Not stated | Not stated |
In each engine
| Engine | Tool | Parameters | Differences |
|---|---|---|---|
gdal | gdal raster tpi |
| None noted |
postgis-raster | st_tpi |
| None noted |
qgis | gdal:tpitopographicpositionindex |
|
|
terra | terra::terrain |
| None noted
Preset: {"v":"TPI"} |
xarray-spatial | xrspatial.tpi |
|
|