Visibility

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Once you have created a surface, Maptitude can perform a visibility analysis. This determines the areas of the map (or surface) that are visible from a point on or above the surface. For example, you could determine the areas of the map that can be reached by a 100m high radio mast. Or you could determine if a power pylon is relatively hidden, or is visible over a large area of the landscape. The visibility information is written to a new area layer on your map.

To perform a visibility analysis, first zoom the map so that it covers the area you wish to analyze. The resulting coverage polygons will be clipped by this window. Next, display the Surface Analysis Toolbox (select Toolbox on the Tools->Surface Analysis sub-menu):

Click the Visibility Analysis button (the eye, third button from left). Next, click on the required location on the map. Maptitude will then display the Visibility Analysis Point dialog box:

The Visibility Analysis Point Dialog box

Set the height above the surface of the analysis point. 2 meters (as above) might be appropriate for a human. For this demo we will enter 100m, which is more appropriate for a radio mast.

It might be tempting to set the height above the surface to be 2m – representing the view that a human would see. This should work, but experience has shown that it is very susceptible to errors in positioning, as well as both horizontal and vertical errors in the digital elevation model (DEM). Such errors become less significant with greater heights.

Once you have set the height, press OK. Next, Maptitude will prompt you for the name of the new geographic file that will store the area visibility layer. Maptitude will then start analyzing the data. Note that this can be time consuming if your surface has a lot of data points or if the area of visibility is wide and/or complex.

Here is an example taken from the Guadalupe Mountains example:

The visibility results. The hatched areas are locations not visible from the red triangle. (click for larger view)

Here we have selected a 100m height (e.g. for a radio mast). Maptitude has marked this location with a solid red triangle annotation marker.

The location is north of the main Guadalupe Mountains, on a small north-south ridge. Areas which are not visible are drawn with green boundaries and black hatching in the new Viewshed layer. Notice that due to the curvature of the ridge, much of it is actually out of view. However, the valleys either side are visible, as are some of the (magenta) mountain peaks in the south. The mountain ridges to the east provide an effective block to visibility: Their western sides are visible, but nothing else is.

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