Tool Name	Topographic Position Index (TPI)
Tool ID	18
Library ID	ta_morphometry
Version	1.0
Author(s)	O.Conrad (c) 2011

Description

Topographic Position Index (TPI) calculation as proposed by Guisan et al. (1999). This is literally the same as the difference to the mean calculation (residual analysis) proposed by Wilson & Gallant (2000). The bandwidth parameter for distance weighting is given as percentage of the (outer) radius.

Parameters

Name	Type	Identifier	Description	Constraints
Input
Elevation	grid, input	DEM
Output
Topographic Position Index	grid, output	TPI
Options
Standardize	boolean	STANDARD		Default: 0
Scale	value range	RADIUS	kernel radius; defines an annulus if minimum is greater than zero
Radius Unit	choice	UNIT		Available Choices: [0] map units [1] cells Default: 0
Weighting Function	choice	DW_WEIGHTING		Available Choices: [0] no distance weighting [1] inverse distance to a power [2] exponential [3] gaussian Default: 0
Power	floating point number	DW_IDW_POWER		Minimum: 0.000000 Default: 2.000000
Bandwidth	floating point number	DW_BANDWIDTH	Bandwidth for exponential and Gaussian weighting	Minimum: 0.000000 Default: 75.000000
Processing Buffer Distance	floating point number	PROC_BUFFER	Width of the buffer added around the central raster area [in radius unit]. Kernel cells within the buffered extent are evaluated, but TPI is calculated only for the inner (non-buffered) area. The buffer distance should match or exceed the maximum kernel radius to avoid edge effects.	Minimum: 0.000000 Default: 0.000000