Topographic Position Index (TPI)

Author(s)	O.Conrad (c) 2011
Library ID	ta_morphometry
Tool ID	18
Version	1.0
Menu	Terrain Analysis \| Morphometry

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	Grid System	grid system	`PARAMETERS_GRID_SYSTEM`	-	-
	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

Command Line


Usage: saga_cmd ta_morphometry 18 [-DEM ] [-TPI ] [-STANDARD ] [-RADIUS_MIN ] [-RADIUS_MAX ] [-UNIT ] [-DW_WEIGHTING ] [-DW_IDW_POWER ] [-DW_BANDWIDTH ] [-PROC_BUFFER ]
  -DEM:               Elevation
	grid, input
  -TPI:               Topographic Position Index
	grid, output
  -STANDARD:          Standardize
	boolean
	Default: 0
  -RADIUS_MIN:     Scale
	value range
  -RADIUS_MAX:     Scale
	value range
  -UNIT:              Radius Unit
	choice
	Available Choices:
	[0] map units
	[1] cells
	Default: 0
  -DW_WEIGHTING:
                           Weighting Function
                           	choice
                           	Available Choices:
                           	[0] no distance weighting
                           	[1] inverse distance to a power
                           	[2] exponential
                           	[3] gaussian
                           	Default: 0
  -DW_IDW_POWER:   Power
	floating point number
	Minimum: 0.000000
	Default: 2.000000
  -DW_BANDWIDTH:   Bandwidth
	floating point number
	Minimum: 0.000000
	Default: 75.000000
  -PROC_BUFFER:    Processing Buffer Distance
	floating point number
	Minimum: 0.000000
	Default: 0.000000