Viewshed
The Viewshed request is used to identify visible areas based on observer locations you provide.
Request URL
https://elevation.arcgis.com/arcgis/rest/services/Tools/Elevation/GPServer/Viewshed/submitJobDescription
The Viewshed request is used to identify visible areas. You specify the places you are interested in, either from a file or interactively, and the Viewshed request combines this with ArcGIS elevation data to create output polygons of visible areas. Some questions you can answer with the Viewshed analysis include the following:
- What areas can I see from this location?
- What areas can see me?
- Can I see the proposed wind farm?
- What areas can be seen from this proposed fire tower location?
Depending on the DEM resolution selected, different data sources will be used by the request.
- By default, this request currently works worldwide between 60 degrees north and 56 degrees south based on the 3 arc-second (approximately 90-meter) resolution SRTM dataset.
- For 30m, the request will use 1 arc-second resolution data in North America (Canada, United States, and Mexico) from the USGS National Elevation Dataset (NED), SRTM DEM-S dataset from Geoscience Australia in Australia and SRTM data between 60 degrees north and 56 degrees south in the remaining parts of the world (Africa, South America, most of Europe and continental Asia, the East Indies, New Zealand, and islands of the western Pacific).
- For 24m, the request will use 0.8 arc-second (approximately 24-meter) data from the global dataset WorldDEM4Ortho from Airbus Defence and Space GmbH, excluding the countries of Azerbaijan, DR Congo, and Ukraine.
- For 10m, the request will use 1/3 arc-second resolution data in the continental United States from USGS National Elevation Dataset (NED) and approximately 10-meter data covering Norway, Finland, Denmark, Austria, Spain, Japan, Latvia, Lithuania, Slovak Republic, Italy, Switzerland, and Liechtenstein from various authoritative sources.
Refer to the locator map to see the areas covered and to learn more about the data sources currently available.
Usage
The request will return an error message if the specified resolution is not available at any of the input feature locations.
If the DEMResolution parameter is empty or not supplied, the resolution of 90 meters will be used.
If FINEST is specified for the parameter, the request will use the smallest resolution available at your observer location that is allowed by the MaximumDistance parameter. This means when the MaximumDistance is less than or equal to 5 kilometers, and for areas where it is available, the 10m resolution data will be used. If the maximum distance is greater than 5 kilometers but less than or equal to 15 kilometers, and where it is available, the 24m resolution data will be used. Otherwise, if the distance is greater than 15 kilometers, the 90m resolution data will be used.
For the MaximumDistance parameter itself, the allowed value for the 10m, 24m, and 30m DEM resolutions is 15 kilometers or less. For the 90m DEM resolution, the allowed value is 50 kilometers or less. If this parameter is not specified, the request will use a default value based on the DEM resolution parameter. For 10m resolution, the default maximum distance is 5 kilometers. For the 24m, 30m, and 90m DEM resolutions, the default distance is 15 kilometers.
The request uses a single-resolution elevation source for the input features. All the input features must fit into a single resolution, or the request will pick the highest resolution that can cover the features.
Visibility into water is limited, so the tool uses the water surface as the elevation. Oceans have been assigned a value of zero, and major water bodies have been assigned an appropriate flat local elevation.
The output viewshed is returned as polygon features. The field named Frequency is used to record the number of observation points that can see each polygon. The field named DEMResolution is used to record the source DEM resolution for the viewshed computation. Three additional fields, which identify the DEM data source used in the calculation, are returned. Those fields are Product Name, Source, and Source URL.
A lower DEM resolution will result in a faster response from the request. For example, the 90m resolution typically has the shortest response time. The tradeoff is that a lower DEM resolution has a lower accuracy in the viewshed result compared to that of a higher DEM resolution.
The MaximumDistance parameter may also affect the response time. In general, using a smaller distance results in a shorter response time.
The maximum number of input points is 1,000. If additional input points are provided, the request will return an error and will not execute.
Request parameters
| Parameter | Description |
|---|---|
InputPoints (Required) | The point features to use as the observer locations.
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MaximumDistance | This is a cutoff distance where the computation of visible areas stops. Beyond this distance, it is unknown whether the analysis points and the other objects can see each other. It is useful for modeling current weather conditions or a given time of day, such as dusk. Large values increase computation time. Unless specified, a default maximum distance will be computed based on the resolution and extent of the source DEM. The allowed maximum value is 50 kilometers. Use MaximumDistanceUnits to set the units for MaximumDistance.
|
MaximumDistanceUnits | The units for the MaximumDistance parameter.
|
DEMResolution | The approximate spatial resolution (cell size) of the source elevation data used for the calculation. The default is 90m. The resolution values are an approximation of the spatial resolution of the digital elevation model. While many elevation sources are distributed in units of arc seconds, the keyword is an approximation of those resolutions in meters for easier understanding.
|
ObserverHeight | This is the height above the ground of the observer locations. The default is 1.75 meters, which is approximately the average height of a person. If you are looking from an elevated location, such as an observation tower or a tall building, use that height instead. Use ObserverHeightUnits to set the units for ObserverHeight.
|
ObserverHeightUnits | The units for the ObserverHeight parameter.
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SurfaceOffset | The height above the surface of the object you are trying to see. The default value is 0.0. If you are trying to see buildings or wind turbines, use their height here.
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SurfaceOffsetUnits | The units for the SurfaceOffset parameter.
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GeneralizeViewshedPolygons | Determines whether the viewshed polygons are to be generalized. The viewshed calculation is based on a raster elevation model that creates a result with stair-stepped edges. To create a more pleasing appearance and improve performance, the default behavior is to generalize the polygons. The generalization process smooths the boundary of the visible areas and may remove some single-cell visible areas.
|
Response
When you submit a request, the request assigns a unique job ID for the transaction.
Syntax:
{
"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 the topic Checking job status. Once the job has successfully completed, use the jobId to retrieve the results. To track the status, you can make a request of the following form:
https://elevation.arcgis.com/arcgis/rest/services/Tools/Elevation/GPServer/Viewshed/jobs/<jobId>
Accessing results
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://elevation.arcgis.com/arcgis/rest/services/Tools/Elevation/GPServer/Viewshed/jobs/<jobId>/results/OutputViewshed?token=<your token>&f=json