Three Parameters of Viewshed Analysis: Viewpoint, Azimuth, & Radius (Especially for GATE-Geospatial 2022)

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Several parameters can influence the result of a viewshed analysis including the viewpoint, the height of the observer, the viewing azimuth, the viewing radius, vertical viewing angle limits, the Earth՚s curvature, and tree height.

Diagram Shows Three Parameters of Viewshed Analysis

The Viewpoint

The first parameter is the viewpoint. A viewpoint located along a ridge line would have a wider view than a viewpoint located in a narrow valley. There are at least two scenarios in dealing with the viewpoint in GIS. The first scenario assumes that the location of the point is fixed. If the elevation at the point is known, it can be entered directly in a field. If not, it can be estimated from an elevation raster or a TIN. ArcGIS, for example, uses bilinear interpolation to interpolate the elevation of a viewpoint from an elevation raster. The second scenario assumes that the viewpoint is to be selected. If we further assume that the objective is to gain maximum visibility, then we would select the viewpoint at a high elevation with open views.

Figure Shows Visible and Invisible of an Elevation Raster

Viewing Azimuth

The second parameter is the viewing azimuth, which sets horizontal angle limits to the view. For example, uses a viewing angle from to . The default is full sweep, which is unrealistic in many instances. To simulate the view from the window of a property, a viewing azimuth is more realistic than a sweep.

Figure Shows the Visible Areas between Viewing Angle in Deg …

Viewing Radius

Viewing radius is the third parameter, which sets the search distance for deriving visible areas. For example, shows viewable areas within a radius of 8000 meters around the viewpoint. The default view distance is typically infinity. The setting of the search radius can vary with project.

Figure Shows the Visible Areas Betweenthe Search Radius

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