The Flow direction operation determines into which neighbouring pixel any water in a central pixel will flow. Flow direction is calculated for every central pixel in input blocks of 3 by 3 pixels, each time comparing the value of the central pixel with the value of its 8 neighbouring pixels. The output map contains flow directions as N (to the North), NE (to the North East), etc.
Dialog box options:
Input DEM: |
Select an input raster map. Open the list box and select the desired input map, or directly drag a raster map from a Catalog into this box. The input map is supposed to be a sink-free Digital Elevation Model (DEM). |
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Select this option when flow direction should be calculated according to the steepest downhill slope between a central pixel and its 8 neighbour pixels. |
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Select this option when flow direction should be simply be calculated as:
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Output raster map: |
Type a name for the output raster map that will contain the flow directions. |
Description: |
Optionally, type a description for the output map. The description will appear in the status bar of the Main window when moving the mouse pointer over the map in a Catalog, and in the title bar of a map window when the output map is displayed. If no description is supplied, the output map will use its own definition as description. |
When you click the Show button, the dependent output map will be defined, calculated and shown. When you click the Define button, the dependent output map will only be defined; if necessary the map will be calculated later, for instance when the map is opened to be displayed.
The output map will always use system domain FlowDirection.
See also: