raster_tools.surface.tpi#

raster_tools.surface.tpi(dem, annulus_inner, annulus_outer)[source]#

Compute the Topographic Position Index of a DEM.

This function compares each elevation value to the mean of its neighborhood to produce a scale-dependent index that highlights ridges (positive values) and valleys (negative valleys). Values close to zero, indicate areas with constant slope such as plains (slope of zero). The basic function looks like this:

tpi = int(dem - focalmean(dem, annulus_inner, annulus_outer) + 0.5)

An annulus (donut) is used to select the neighborhood of each pixel. Larger radii values select features at larger scales.

Parameters

  • dem (Raster or path str) – The DEM raster to use for TPI analysis.

  • annulus_inner (int) – The inner radius of the annulus. If 0, a circle of radius annulus_outer is used to select the neighborhood.

  • annulus_outer (int) – The outer radius of the annulus. Must be greater than annulus_inner.

Returns

tpi – The resulting TPI index for dem at the scale determined by the annulus radii.

Return type

Raster

References