Surface Analyst > Viewshed

Viewshed

With Viewshed tool, the visible locations for one or multiple observer points or lines can be determined. Every observer point is located at different elevation, so the visible location differs. In the output value, the cell that is visible from the observer point is assigned 1; the cell that is invisible from the observer point is assigned 0. Observer point or line is acceptable. As to the observer line, its vertices will be treated and used as the observer points.

See the figure above, a man is standing at the centroid higher than the lawn, house and woods, so he can see all the spots mentioned. In the figure, the blue part refers the visible extent, green refers the invisible extent. To some locations, they are invisible due to being hidden by the foreground.

Description of Parameters

Item	Description	Data Type
Input Surface	The data to perform Viewshed analysis.	Raster layer
Observer Data	The location to observe, the maximum allowable number of points is 16.	Feature layer(point, line)
Z Factor	The default is 1; it means the unit of vertical and horizontal direction are the same.	Integer/Floating point
Cell Size	The cell size of output raster.	Integer/Floating point
Output Raster	The filename and storage path of the output raster(the output can be two kinds of value, 0 and 1. 0 represents invisible area, 1 represents the visible area ).	Raster layer

Flexible parameters for visibility:

ViewShed supports multiple parameters such as height observation, angle observation, etc.

Parameters’ setting and explanation are listed below:

Item	Description
Surface offset	This parameter, whose default value is 0, is used to set the elevation value adding on the height value of the observation point. Let’s give an example: This parameter can be applied to specify the height of the observation point surrounded by woods while conducting viewshed analysis. If the height of woods surrounding the observation point is 1 meter; users have to set a value of surface offset as 1m. And then viewshed analysis will be conducted based on the height value and surface offset value and the height value. Finally, the surface will be 1 meter higher than the input surface.
Observer elevation	This parameter is used to set height of an observation point. The default value of the observation point is the height value detected from the DTM.
Observer offset	This parameter is used to set height of an observation location. Users can apply this parameter to set height of the observation locations such as stations, buildings. The default value is 0.
Inner radius	The parameter, inner radius, defines the start distance of visible range. Cells closer than the inner radius are invisible in the output but considered in the analyst. The gray part in the figure below shows the visible range. The inner radius and outer radius help users define a visual range and make analyst result more realistic to the real world.
Outer radius	This value specifies the maximum distance of visible range. Cells beyond the outer radius are excluded from the analysis. The default value is infinite; you can select a field to specify different values for each observer or assign a value to all.
AZIMUTH1	Horizontal field of view 1 (Horizontal FOV 1), whose default value is 0 degree.
AZIMUTH2	Horizontal field of view (Horizontal FOV 2), whose default value is 360 degree. To get the horizontal vision angle of observation location, please subtract value of AZIMUTH1from value of AZUMUTH2 by setting the two parameters. You can refer to the figure below:
VERT1	The vertical field of view (Vertical FOV 1) whose degree is defined from the observation location to the upper horizontal plane. The default degree is 90 degree.
VERT2	The vertical field of view 2 (Vertical FOV 2) whose degree is defined from the observation location to the lower horizontal plane. The default degree is -90 degree. The vertical viewshed of observation location contains vision angle of VERT2 and of VERT1.