Feature Description
Flow direction refers to the direction in which surface water flows across a hydrologic surface. Calculate the flow direction is one of the key steps in hydrology analysis. Many hydrological functions rely on a flow direction raster, such as calculating cumulative flow accumulation, flow length, and watersheds.
In SuperMap, the eight neighboring raster cells around the center cell are encoded. The encoding uses powers of 2. Starting from the cell directly to the right of the center cell and proceeding clockwise, the encoding values are 2 to the power of 0, 1, 2, 3, 4, 5, 6, 7, which correspond to 1, 2, 4, 8, 16, 32, 64, 128. These represent the eight possible flow directions from the center cell: East, Southeast, South, Southwest, West, Northwest, North, and Northeast, as shown in the figure below. The flow direction for each center cell is determined by one of these eight values. For example, if the flow direction from the center cell is West, its flow direction value is assigned 16; if the flow direction is East, the value is assigned 1.
Parameter description
| Parameter Name | Default Value | Parameter Interpretation | Parameter Type |
|---|---|---|---|
| Original Terrain Data | Original terrain data | DatasetGrid | |
| Force boundary raster flow out | false | Whether to set the flow direction of boundary cells to flow outward. True means water from all grid cells at the edge of the raster surface flows outward. | Boolean |
| Target Datasource | The specified datasource where the resulting dataset will be stored. | Datasource | |
| Flow direction grid dataset name | Name of the resulting flow direction grid dataset. | String | |
| Drop grid dataset name （Optional） |
dropGrid | Name of the resulting drop grid dataset. | String |
| Create the drop grid （Optional） |
false | Whether to create the drop grid. When true, the process of calculating the flow direction will also compute the elevation change gradient for each cell, outputting a drop raster. This option is not selected by default, meaning the drop raster will not be created. | |
| Boolean |
Output Result
| Parameter Name | Parameter Interpretation | Parameter Type |
|---|---|---|
| Result direction dataset | Resulting flow direction raster dataset. | DatasetGrid |
| Result drop dataset | Resulting drop dataset. If the creation of a drop raster is not specified, null will be returned. | DatasetGrid |