Available with ArcGIS Image for ArcGIS Online.
The Geodesic Viewshed tool identifies the locations on a raster surface that are visible to the input observer locations.
The output is a hosted imagery layer.
Note:
Geodesic Viewshed was named Create Viewshed in Map Viewer Classic.
Example
A GIS analyst wants to evaluate the visual impact of a proposed wind turbine. Using an input observer point from the top of a wind turbine and an input elevation surface, this tool will create a viewshed output representing the areas that are visible from the wind turbine.
Usage notes
Geodesic Viewshed includes configurations for input layers, viewshed settings, and result layers.
Input layers
The Input layers group includes the following parameters:
Input elevation surface specifies the elevation raster that will be used to calculate the viewshed.
If the vertical unit of the input surface is different from the horizontal unit, such as when the elevation values are represented in feet but the coordinate system is in meters, the surface must have a defined vertical coordinate system. This is because the tool uses the vertical (z) and horizontal (x,y) units to compute a z-factor for the viewshed analysis. Without a vertical coordinate system and no z-unit information available, it is assumed that the z-unit is the same as the x,y-unit. The result is that an internal z-factor of 1.0 will be used for the analysis, which may cause unexpected results.
The data type of the elevation surface can be integer or floating point.
Input observer point or line features specifies the observer locations that will be used to calculate the viewshed. You can choose a layer using the Layer button or use the Draw input features button to create a sketch layer to use as the input.
The input features can contain attribute fields that define various properties of the observers, such as maximum viewing distance or the height of observers.
Viewshed settings
The Viewshed settings group includes the following parameters:
Optimize for specifies the optimization method that will be used to calculate the viewshed.
Speed—Processing speed will be optimized over accuracy for better performance.
Accuracy—Accuracy in the results will be optimized over processing speed. This is the default.
Vertical error specifies the amount of uncertainty in the elevation values of the input elevation surface.
Refractivity coefficient specifies the coefficient of the refraction of visible light in air.
The Observer parameters group includes the following parameters:
Maximum viewing distance specifies the distance at which the computation of visible areas will stop. Beyond this distance, whether the observer points and the other objects can see each other will not be determined. The options are as follows:
Value—A specified linear unit value will be used. This is the default.
Field—The values in a specified field will be used. The field can be numerical or string type.
The field specified for an observer parameter can be a string type that contains a numerical value and a unit. For example, if a string field is specified for maximum viewing distance, it can contain values such as 15 kilometers.
Computation time will increase as the maximum viewing distance increases. Unless a maximum viewing distance is provided, a default maximum distance will be computed based on the resolution and extent of the input elevation surface.
This parameter is useful for modeling certain phenomena. For example, by limiting the extent of visibility, you can model weather conditions such as a light fog. Similarly, restricting the visibility extent can provide control over the time of day by approximating the effect of dusk.
Minimum viewing distance specifies the distance at which the computation of visible areas will begin. Cells on the surface closer than this distance are not visible in the output but can block visibility of the cells between the minimum and maximum viewing distances. The options are as follows:
Value—A specified linear unit value will be used. This is the default.
Field—The values in a specified field will be used. The field can be numerical or string type.
The field specified for an observer parameter can be a string type that contains a numerical value and a unit. For example, if a string field is specified for minimum viewing distance, it can contain values such as 5 kilometers.
This parameter is useful for controlling the viewshed analysis area at a specific distance from the observer. For example, if you are evaluating the visibility from a building top to a distant park, you can set a minimum viewing distance to exclude the areas close by that are of no interest. This will also produce a better processing speed.
Viewing distances are 3D specifies whether the minimum and maximum viewing distance parameters will be measured in 3D distance or 2D distance. The options are as follows:
Checked—The viewing distances will be treated as 3D distances.
Unchecked—The viewing distances will be treated as 2D distances. This is the default.
A 2D distance is the simple linear distance measured between an observer and the target using their projected locations at sea level. A 3D distance provides a more realistic value by taking their relative heights into consideration.
Elevation of observer locations specifies the surface elevation of the observer locations. The options are as follows:
Value—A specified linear unit value will be used. This is the default method.
Field—The values in a specified field will be used. The field can be numerical or string type.
The field specified for an observer parameter can be a string type that contains a numerical value and a unit. For example, if a string field is specified for elevation of observer locations, it can contain values such as 1500 meters.
If this parameter is not specified, the observer elevation will be obtained from the input elevation surface using bilinear interpolation. If a numerical field is provided, the value contained in the field must be in the same unit as the z-unit of the input elevation surface.
Observer height specifies the height above ground for the observer locations. The options are as follows:
Value—A specified linear unit value will be used. This is the default.
Field—The values in a specified field will be used. The field can be numerical or string type.
For example, if you are viewing from an elevated location, such as a building, provide the height of the building.
The field specified for an observer parameter can be a string type that contains a numerical value and a unit. For example, if a string field is specified for observer height, it can contain values such as 10 meters.
Target height specifies the height of a target on the ground that establishes visibility. The options are as follows:
Value—A specified linear unit value will be used. This is the default.
Field—The values in a specified field will be used. The field can be numerical or string type.
For example, if the input points represent wind turbines and you want to determine where people standing on the ground can see the turbines, provide the average height of a person (approximately 6 feet).
The field specified for an observer parameter can be a string type that contains a numerical value and a unit. For example, if a string field is specified for target height, it can contain values such as 6 meters.
Horizontal start angle specifies the start angle of the horizontal scan range. The angle can be between 0 to 360 degrees, with 0 degrees orienting to the north. The options are as follows:
Value—A specified value will be used. It must be a positive integer or floating-point number; the default value is 0 degrees. This is the default.
Field—The values in a specified field in the Input observer point or line features value will be used.
Horizontal end angle specifies the end angle of the horizontal scan range. The angle can be between 0 to 360 degrees, with 0 degrees orienting to the north. The options are as follows:
Value—A specified value will be used. It must be a positive integer or floating-point number; the default value is 360 degrees. This is the default.
Field—The values in a specified field in the Input observer point or line features value will be used.
Vertical upper angle specifies the upper vertical angle limit of the scan relative to the horizontal plane. The angle can be between -90 to 90 degrees, with 90 degrees facing straight up and –90 degrees facing straight down. The options are as follows:
Value—A specified value will be used. It must be an integer or floating-point number; the default value is 90 degrees. This is the default.
Field—The values in a specified field in the Input observer point or line features value will be used.
Vertical lower angle specifies the lower vertical angle limit of the scan relative to the horizontal plane. The angle can be between -90 to 90 degrees, with 90 degrees facing straight up and –90 degrees facing straight down. The options are as follows:
Value—A specified value will be used. It can be an integer or floating-point number; the default value is -90 degrees. This is the default.
Field—The values in a specified field in the Input observer point or line features value will be used.
Result layers
The Result layers group includes the following parameters:
Output viewshed raster name specifies the name of the output raster that contains the viewshed result.
The name must be unique. If a layer with the same name already exists in your organization, the tool will fail and you will be prompted to use a different name.
The Optional layers group includes the following parameter:
Output above ground level raster name specifies the name of the optional output raster that contains the above ground level (AGL) result.
The name must be unique. If a layer with the same name already exists in your organization, the tool will fail and you will be prompted to use a different name.
- Output layer type specifies the type of raster output that will be created. The output can be either a tiled imagery layer or a dynamic imagery layer.
- Save in folder specifies the name of a folder in My Content where the result will be saved.
Environments
Analysis environment settings are additional parameters that affect a tool's results. You can access the tool's analysis environment settings from the Environment settings parameter group.
This tool honors the following analysis environments:
- Cell size
- Mask
- Output coordinate system
- Processing extent
Note:
The default processing extent in Map Viewer is Full extent. This default is different from Map Viewer Classic in which Use current map extent is enabled by default.
- Snap raster
Outputs
This tool includes the following outputs:
- The Output viewshed raster name layer stores the number of observers that can see each cell location.
- The Output above ground level raster name layer stores the AGL result in each cell, which is the minimum height that must be added to a cell that is otherwise not visible to make it visible by at least one observer. Cells that are visible will be assigned 0 in this output raster.
Usage requirements
This tool requires the following licensing and configurations:
- Creator or GIS Professional user type
- Publisher, Facilitator, or Administrator role, or an equivalent custom role
- ArcGIS Image for ArcGIS Online
Resources
Use the following resources to learn more:
- How Geodesic Viewshed works
- Create Viewshed in ArcGIS REST API
- create_viewshed in ArcGIS API for Python
- Create Viewshed in ArcGIS Pro with the Raster Analysis extension
- Geodesic Viewshed in ArcGIS Pro with the Spatial Analyst extension