| Tool Name | Convergence Index |
| Tool ID | 1 |
| Library ID | ta_morphometry |
| Version | 1.0 |
| Author(s) | O.Conrad (c) 2001 |
This tool calculates an index of convergence (or divergence) with respect to overland flow direction. Its meaning is similar to that of plan or horizontal curvature, but produces much smoother results. The calculation uses the aspects of surrounding cells, i.e. it looks to which degree surrounding cells point to the center cell. Index values are percentages, with negative values corresponding to convergent, positive to divergent flow conditions. Plus 100 would be the peak of a summit, 0 an even slope, and minus 100 a pit.
Fig. 1: Examples for index values with arrows indicating the aspect direction (a=+100%, b=0%, c=-100%).
Fig. 2: Real landscape example with contour lines and arrows indicating aspect direction.
Conrad, O. (1998): Ableitung hydrologisch relevanter Reliefparameter aus einem Digitalen Geländemodell (am Beispiel des Einzugsgebietes Linnengrund / Kaufunger Wald). Diploma Thesis, Dept. of Geography, University of Göttingen. online
Kiss, R. (2004): Determination of drainage network in digital elevation models, utilities and limitations. Journal of Hungarian Geomathematics, 2, 16–29. online
Köthe, R. & Lehmeier, F. (1996): SARA - System zur Automatischen Relief-Analyse. User Manual, 2. Edition, Dept. of Geography, University of Göttingen [unpublished].
| Name | Type | Identifier | Description | Constraints |
|---|---|---|---|---|
| Input | ||||
| Elevation | grid, input | ELEVATION | ||
| Output | ||||
| Convergence Index | grid, output | RESULT | ||
| Options | ||||
| Directions | choice | METHOD | Use either aspect only or the full gradient (including the sloping). | Available Choices: [0] Aspect [1] Gradient Default: 0 |
| Neighbourhood | choice | NEIGHBOURS | Neighbourhood used for aspect/slope calculation. Chosing '3x3' will give smoother results than '2x2'. | Available Choices: [0] 2 x 2 [1] 3 x 3 Default: 1 |