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