Using the ArcGIS Spatial Analyst toolbar to calculate Viewshed
Release 9.2 Last modified May 2, 2007

About calculating viewshed

By calculating viewshed, the cells in an input raster that can be seen from one or more observation points or lines can be identified.
This is useful for applications in which the visibility of an object is important—such as finding well-exposed places for communications towers.
You can control the visibility in the Viewshed tool by setting some optional parameters. To use the optional parameters OFFSETA, OFFSETB, RADIUS1, and so on, add these fields to the feature attribute table. Each feature can have different values for these parameters. Once these fields are added, they will automatically be used when you open the Viewshed tool.
Learn more about optional parameters
Learn more about calculating viewshed
Learn how to calculate viewshed using the Viewshed tool
Learn about other Spatial Analyst toolbar functions

How to calculate viewshed

Calculating viewshed

1. Click the Spatial Analyst dropdown arrow, point to Surface Analysis, and click Viewshed.
   
2. Click the Input surface dropdown arrow and click the input surface from which you want to calculate the viewshed.
   
3. Click the Observer points dropdown arrow and click the feature layer to use as observer points.
   
4. Specify a z-factor if your z units are in a different unit of measure than your x,y units.
   
5. Optionally, change the default Output cell size.
   
6. Specify a name for the output raster, or leave the default to create a temporary dataset in your working directory.
   
7. Click OK.
   

Tips

The z-factor is the number of ground x,y units in one surface z unit. The Input surface values are multiplied by the specified z-factor to adjust the input surface z units to another unit of measure. It is important to specify a z-factor if the z units are not in the same unit of measure as the x,y units. For instance, if your x and y units are in meters and your z units are in feet, you would specify a z-factor of 0.3048, since there are 0.3048 meters in one foot. Optional viewshed parameters (SPOT, OFFSETA, OFFSETB, AZIMUTH1, AZIMUTH2, VERT1, and VERT2) will be used if they are present in the feature observer attribute table.

Controlling visibility in a viewshed

1. Click the View menu in ArcMap, point to Toolbars, then check the check box next to Editor to open the Editor toolbar.
   
2. Right-click the Observer point layer and click Open Attribute table.
   
3. Click the Options button and click Add Field.
   
4. Enter the name for the field of the optional parameter, for example, OFFSETA, and modify the other default options if necessary.
   
5. Click the Editor menu and click Start Editing.
   
6. Enter the values for the OFFSETA field into the table.
   
7. Repeat steps 3 through 6 for other fields.
   
8. Click the Editor menu and click Stop Editing.
   
9. Click Yes to save your edits.
   

Tip

SPOT, OFFSETA, OFFSETB, AZIMUTH1, AZIMUTH2, VERT1, and VERT2 store visibility parameters in the Feature Attribute table.

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