Summary
Computes, for each cell, the horizontal or vertical component of downslope distance, following the flow paths, to cells on a stream into which they flow. In the case of multiple flow paths, minimum, weighted mean, or maximum flow distance can be computed.
If an optional flow direction raster is provided, the down slope directions will be limited to those defined by the input flow direction raster.
Illustration
Usage
This raster analysis portal tool is available when you are signed in to an ArcGIS Enterprise
portal that has an ArcGIS Image Server configured for Raster Analysis . When the tool is invoked, ArcGIS Pro serves as a client and the processing occurs in the servers federated with ArcGIS Enterprise. The portal tool accepts layers from your portal as input and creates output in your portal.The input raster layer supports a layer from the portal, a URI or URL to an image service, or the output from the Make Image Server Layer tool. This tool does not support local raster data or layers.
To limit downslope directions along which flow distance is measured, provide an optional input flow direction raster that can be derived using the Flow Direction tool. Choose from D8, D-Infinity (DINF) and multi flow direction (MFD) flow models while generating an optional input flow direction raster. Use the Input flow direction type to specify which method was used when the flow direction raster was created.
If an optional input flow direction raster is provided, it is recommended that this raster be created using the Flow Direction tool using the same input surface raster that you'll provide to the Flow Distance tool.
If this input surface raster is void of sinks, the distance measurements will be to stream cells represented by the input stream raster.
If this input surface raster has sinks present, some flow paths can be terminated short by them flowing into sinks before reaching streams. In such cases, flow distance measurements for these cells are calculated only up to the sink cells into which they flow.
When the tool is run without an optional flow direction raster, flow distance is assessed by considering all possible downslope flow paths from each cell to cell(s) on a stream into which they flow.
When the tool is run with an optional D8 flow direction raster, there is only one possible downslope flow path from every cell to a cell on the stream, and flow distance is measured along this single flow path.
It is recommended to create the input stream raster using the same input surface raster that is provided as input to the tool. If you have a Spatial Analyst extension license available, you can create stream rasters from an input surface raster using the Flow Direction, Flow Accumulation and Con tools respectively. If you wish to use streams from other data sources, for best results, you would have to burn them into the input surface raster first and then running the Flow Distance tool.
When multiple flow paths exist from each cell to cells on the stream into which they flow, use the Statistics type to compute minimum, weighted mean, or maximum flow distance.
If there exists only a single flow path from each cell to a cell on the stream, all statistics types produce the same result.
Syntax
arcpy.ra.FlowDistance(inputStreamRaster, inputSurfaceRaster, outputName, {inputFlowDirectionRaster}, {distanceType}, {flowDirectionType}, {statisticsType})| Parameter | Explanation | Data Type |
inputStreamRaster | The input raster that defines the stream network. | Raster Layer; Image Service; String |
inputSurfaceRaster | The input raster representing a continuous surface. | Raster Layer; Image Service; String |
outputName | The name of the output flow distance raster service. The default name is based on the tool name and the input layer name. If the layer name already exists, you will be prompted to provide another name. | String |
inputFlowDirectionRaster (Optional) | The input raster that shows the direction of flow out of each cell. When a flow direction raster is provided, the down slope direction(s) will be limited to those defined by the input flow directions. The flow direction raster can be created using the D8, MFD, or DINF method. Use the flowDirectionType parameter to specify the method used when the flow direction raster was created. | Raster Layer; Image Service; String |
distanceType (Optional) | The distance type to be calculated.
| String |
flowDirectionType (Optional) | Specifies the input flow direction raster type.
| String |
statisticsType (Optional) | Determines the statistics type used to compute flow distance over multiple flow paths. If there exists only a single flow path from each cell to a cell on the stream, all statistics types produce the same result.
| String |
Derived Output
| Name | Explanation | Data Type |
| outputRaster | The output raster. | Raster Layer |
Code sample
This example calculates the minimum downslope horizontal flow distance to a cell on the stream raster.
import arcpy
arcpy.FlowDistance_ra("https://myserver/rest/services/streams/ImageServer","https://myserver/rest/services/elevation_fill/ImageServer","outFlowDistanceVertical1")This example calculates the minimum downslope vertical flow distance to a cell on the stream raster.
#---------------------------------------------------------------------------
# Name: FlowDistance_example02.py
# Requirements: ArcGIS Image Server
# Import system modules
import arcpy
# Set local variables
inStreams = "https://myserver/rest/services/streams/ImageServer"
inSurface = "https://myserver/rest/services/elevation_fill/ImageServer"
outputFlowDistance = "outFlowDistanceVertical2"
inFlowDirection = ""
distanceType = "VERTICAL"
# Execute Flow Distance raster analysis tool
arcpy.FlowDistance_ra(inStreams, inSurface, outputFlowDistance, inFlowDirection, distanceType)Environments
Licensing information
- Basic: Requires ArcGIS Image Server
- Standard: Requires ArcGIS Image Server
- Advanced: Requires ArcGIS Image Server