Thursday, August 4, 2016

Software Scenario Functions: Visibility Analysis

The portion of the terrain that can be seen from any particular elevation is known as viewshed. The process of visibility and intervisibility at a particular point on a topographic surface is called viewshed analysis or visibility analysis.

Some of the uses of this technique are:

  1. Siting television, radio and cellular phone transmitters and receiving stations
  2. Locating towers for observing forest fires
  3. Routing highways that are not visible to nearby residents
Visibility analysis is useful in planning that requires features to be either visible or concealed .

The simplest method is to connect an observer location to every possible target location.
In the next step, ray tracing is carried out. This is done by following the line from the target point back to the observer point. Higher points obstruct the observer's view.
Among the many possible ways to determine intervisibility, the ray tracing technique is simple and useful, although it is less accurate.

Visibility analysis requires the use of a Triangulated Irregular Network (TIN) data model in which the surface is defined by triangular vertices.

Example: Consider a builder constructing houses at the foothills of a mountain range and desires to present a beautiful view of the landscape from the location of each house. After shortlisting the potential locations, the TIN model for each location is used by the GIS software to look in all directions at the vertices for a view from the vertices of the model. The software retrieves the elevation values and compares these values with the elevation of potential building sites. All the areas higher in elevation are classified as invisible. The resulting polygon map shows visible areas for each coverage tested.
Raster methods of visibility analysis are similar except that they are less elegant and more computationally expensive.