ArcGIS REST API

Flow Accumulation

Description

Flow Accumulation task

The Flow Accumulation task creates a raster of accumulated flow into each cell. A weight factor can optionally be applied.

The result of this task is a raster of accumulated flow to each cell determined by accumulating the weight for all cells that flow into each downslope cell.

The task supports three flow modeling algorithms while computing accumulated flow. These are the D8, Multiple Flow Direction (MFD), and D-Infinity (DINF) flow methods.

If the input flow direction raster is not created with the FlowDirection task, there is a chance that the defined flow could loop. If the flow direction contains a loop, the Flow Accumulation task will go into an endless cycle and never finish.

Input flow direction can be created using the D8, MFD, or DINF method. The type of input flow direction raster between these three influences how the FlowAccumulation task partitions and accumulates flow in each cell. Use the flowDirectionType parameter to specify which method was used when the flow direction raster was created.

Additional details on how flow accumulation is calculated

  • The accumulated flow is based on the number of total or a fraction of cells flowing into each cell in the output raster. The current processing cell is not considered in this accumulation.
  • Output cells with a high flow accumulation are areas of concentrated flow and can be used to identify stream channels.
  • Output cells with a flow accumulation of zero are local topographic highs and can be used to identify ridges.
  • Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow.
  • For an input D8 flow direction raster, a cell is considered to have an undefined flow direction if its value in the flow direction raster is anything other than 1, 2, 4, 8, 16, 32, 64, or 128.
  • For an input DINF flow direction raster, a cell is considered to have an undefined flow direction if its value in the flow direction raster is -1.

Request parameters

ParameterDetails
inputFlowDirectionRaster

(Required)

The input raster that shows the direction of flow out of each cell.

Syntax: This parameter can be specified as a Portal Item ID, a URL to a raster image service layer, a cloud raster dataset, or a shared raster dataset.

Examples:

//Portal item as input raster
"inputFlowDirectionRaster": {"itemId": <portal item id>}

//URL as input raster
"inputFlowDirectionRaster": {"url": <image service layer url>}

outputName

(Required)

The output image service name that will be created.

You can specify the name, or you can create an empty service using Portal Admin Sharing API and use the return JSON object as input to this parameter.

Syntax: A JSON object describes the name of the output or the output raster.

Output name example:

"outputName":{"serviceProperties":{"name":"testrasteranalysis"}}

Output raster examples:

//Output portal item:
"outputName":{"itemId": <portal item id>}

//Output url:
"outputName":{"url": <image service url}

//Output raster layer service:
"outputName":{"serviceProperties":
  {"name":"testrasteranalysis",
    "serviceUrl":"https://<server name>/server/rest/services/Hosted/testrasteranalysis/ImageServer"},
  "itemProperties":{"itemId":"8cfbd3ec25584d0d8f4ed23b8ff7c43b","folderId":"sdfwerfbd3ec25584d0d8f4"}
}

inputWeightRaster

An optional input raster for applying a weight to each cell.

Syntax: This parameter can be specified as a Portal Item ID, a URL to a raster image service layer, a cloud raster dataset, or a shared raster dataset.

Examples:

//Portal item as input raster
"inputWeightRaster": {"itemId": <portal item id>}

//URL as input raster
"inputWeightRaster": {"url": <image service layer url>}

dataType

The output accumulation raster can be one of several different data types.

Syntax: A string describing the data type, which can either be one of the following:

  • FLOAT: The output raster will be floating-point type. This is the default.
  • INTEGER: The output raster will be integer type
  • DOUBLE: The output raster will be double precision (64-bit) floating-point type.

Example:

"dataType": "DOUBLE"

flowDirectionType

The input flow direction raster can be of type D8, Multi Flow Direction (MFD), or D-Infinity (DINF).

Syntax: A string describing the flow direction type, which can be one of the following:

  • D8 is for the D8 flow direction type. This is the default.
  • MFD is for the Multi Flow Direction type.
  • DINF is for the D-Infinity type.

Example:

"flowDirectionType": "DINF"

context

Contains additional settings that affect task execution. This task has the following settings:

  • Extent (extent): A bounding box that defines the analysis area.
  • Output Spatial Reference (outSR): The output raster will be projected into the output spatial reference.
  • Snap Raster (snapRaster): The output raster will have its cells aligned with the specified snap raster.
  • Cell Size (cellSize): The output raster will have the resolution specified by cell size.
  • Mask (mask): Only cells that fall within the analysis mask will be considered in the operation.
f

The response format. The default response format is html.

Values: html | json

Response

When you submit a request, the task assigns a unique job ID for the transaction.

{
  "jobId": "<unique job identifier>",
  "jobStatus": "<job status>"
}

After the initial request is submitted, you can use the jobId to periodically check the status of the job and messages as described in Checking job status. Once the job has successfully completed, you use the jobId to retrieve the results. To track the status, you can make a request of the following form:

https://<raster analysis tools url>/FlowAccumulation/jobs/<jobId>

When the status of the job request is esriJobSucceeded, you can access the results of the analysis by making a request of the following form:

https://<raster analysis tools url>/FlowAccumulation/jobs/<jobId>/results/outputRaster

Example usage

Below is a sample request URL for FlowAccumulation.

https://services.myserver.com/arcgis/rest/services/System/RasterAnalysisTools/GPServer/FlowAccumulation/submitJob

JSON response example

The response returns the outputRaster output parameter, which has properties for parameter name, data type, and value. The content of value is always the output raster dataset itemId and the image service URL.

{
  "paramName": "outRaster",
  "dataType": "GPString",
  "value": {
    "itemId": "f121390b85ef419790479fc75b493efd", 
    "url": "https://<server name>/arcgis/rest/services/Hosted/<service name>/ImageServer"
  }
}