Valley and Ridge Detection (Top Hat Approach)
- Author: O.Conrad (c) 2013
- Menu: Terrain Analysis | Terrain Classification
Description
The tool allows one to calculate fuzzy valley and ridge class memberships from a DEM using the Top Hat approach. The mathematical morphology functions "Opening" and "Closing" form the basis of "The Top Hat Transform" function. The function extracts peaks and valleys with a size condition corresponding to the size of the considered structuring element.
Peaks are extracted by the "White Top Hat" (WTH) function:
WTH = DEM - Opening >= t
Valleys are extracted by the "Black Top Hat" (BTH) function:
BTH = Closing - DEM >= t
The threshold value "t" works as an additional cut-off to extract only the highest peaks and deepest valleys. This means that the functions permit extracting peaks and valleys based on width and height criterions. For details see the referenced paper.
The tool is based on the AML script 'tophat' by Jochen Schmidt, Landcare Research.
References
- Rodriguez, F., Maire, _., Courjault-Rad_, P., Darrozes, J. (2002): The Black Top Hat function applied to a DEM: A tool to estimate recent incision in a mountainous watershed (Estib_re Watershed, Central Pyrenees). Geophysical Research Letters, 29(6): 9-1 - 9-4. doi:10.1029/2001GL014412.
Parameters
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | Elevation | grid, input | DEM | - | - |
| Output | Valley Depth | grid, output, optional | VALLEY | - | - |
| Hill Height | grid, output, optional | HILL | - | - |
| Valley Index | grid, output | VALLEY_IDX | - | - |
| Hill Index | grid, output | HILL_IDX | - | - |
| Hillslope Index | grid, output, optional | SLOPE_IDX | - | - |
| Options | Grid System | grid system | PARAMETERS_GRID_SYSTEM | - | - |
| Valley Radius | floating point number | RADIUS_VALLEY | The radius used to fill valleys [map units]. | Minimum: 0.000000
Default: 1000.000000 |
| Hill Radius | floating point number | RADIUS_HILL | The radius used to cut hills [map units] | Minimum: 0.000000
Default: 1000.000000 |
| Elevation Threshold | floating point number | THRESHOLD | The elevation threshold used to identify hills/valleys [map units]. | Minimum: 0.000000
Default: 100.000000 |
| Slope Index | choice | METHOD | Choose the method to calculate the slope index. | Available Choices:
[0] default
[1] alternative
Default: 0 |
Command Line
Usage: saga_cmd ta_morphometry 24 [-DEM ] [-VALLEY ] [-HILL ] [-VALLEY_IDX ] [-HILL_IDX ] [-SLOPE_IDX ] [-RADIUS_VALLEY ] [-RADIUS_HILL ] [-THRESHOLD ] [-METHOD ]
-DEM: Elevation
grid, input
-VALLEY: Valley Depth
grid, output, optional
-HILL: Hill Height
grid, output, optional
-VALLEY_IDX: Valley Index
grid, output
-HILL_IDX: Hill Index
grid, output
-SLOPE_IDX: Hillslope Index
grid, output, optional
-RADIUS_VALLEY: Valley Radius
floating point number
Minimum: 0.000000
Default: 1000.000000
-RADIUS_HILL: Hill Radius
floating point number
Minimum: 0.000000
Default: 1000.000000
-THRESHOLD: Elevation Threshold
floating point number
Minimum: 0.000000
Default: 100.000000
-METHOD: Slope Index
choice
Available Choices:
[0] default
[1] alternative
Default: 0