Module Topographic Position Index (TPI)
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.
References:
- Guisan, A., Weiss, S.B., Weiss, A.D. (1999): GLM versus CCA spatial modeling of plant species distribution. Plant Ecology 143: 107-122.
- Weiss, A.D. (2000): Topographic Position and Landforms Analysis. poster.
- Wilson, J.P. & Gallant, J.C. (2000): Terrain Analysis - Principles and Applications.
- Author: O.Conrad (c) 2011
- Specification: grid
- Menu: Terrain Analysis|Morphometry
Parameters
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | Elevation | Grid (input) | DEM | - | - |
| Output | Topographic Position Index | Grid (output) | TPI | - | - |
| Options | Standardize | Boolean | STANDARD | - | Default: 0 |
| Radius | Value range | RADIUS | radius in map units | - |
| Weighting Function | Choice | DW_WEIGHTING | - | Available Choices:
[0] no distance weighting
[1] inverse distance to a power
[2] exponential
[3] gaussian weighting
Default: 0 |
| Inverse Distance Weighting Power | Floating point | DW_IDW_POWER | - | Minimum: 0.000000
Default: 1.000000 |
| Inverse Distance Offset | Boolean | DW_IDW_OFFSET | Calculates weights for distance plus one, avoiding division by zero for zero distances | Default: 1 |
| Gaussian and Exponential Weighting Bandwidth | Floating point | DW_BANDWIDTH | - | Minimum: 0.000000
Default: 75.000000 |
Command-line
Usage: saga_cmd ta_morphometry 18 -DEM <str> [-TPI <str>] [-STANDARD <str>] [-RADIUS_MIN <str>] [-RADIUS_MAX <str>] [-DW_WEIGHTING <str>] [-DW_IDW_POWER <str>] [-DW_IDW_OFFSET <str>] [-DW_BANDWIDTH <str>]
-DEM:<str> Elevation
Grid (input)
-TPI:<str> Topographic Position Index
Grid (output)
-STANDARD:<str> Standardize
Boolean
Default: 0
-RADIUS_MIN:<str> Radius
Value range
-RADIUS_MAX:<str> Radius
Value range
-DW_WEIGHTING:<str> Weighting Function
Choice
Available Choices:
[0] no distance weighting
[1] inverse distance to a power
[2] exponential
[3] gaussian weighting
Default: 0
-DW_IDW_POWER:<str> Inverse Distance Weighting Power
Floating point
Minimum: 0.000000
Default: 1.000000
-DW_IDW_OFFSET:<str> Inverse Distance Offset
Boolean
Default: 1
-DW_BANDWIDTH:<str> Gaussian and Exponential Weighting Bandwidth
Floating point
Minimum: 0.000000
Default: 75.000000