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DTMs have the advantage of faster processing by computer, and provided a suitable grid density is used they provide a mathematically better representation of the terrain. Grid densities of 100 meters or better are suitable for aviation.

In addition to the elevation data some DTMs also contain feature codes or surface roughness information for each grid point. Feature codes specify the type of terrain such as bush, urban areas, or water.

DTM navigation is a term which describes low level free flight against a digital terrain model.

A moving 3D display of the terrain in front of the aircraft is shown along with all known obstacles. Even though the aircraft may be in low cloud, fog, or white-out conditions, it can still be navigated as freely as if the aircraft was in visual meteorological conditions (VMC).

DTM Navigation Display

Modern high performance processors and 3D graphics software make this type of display possible. Advanced lighting techniques and surface texturing is also becoming a practical reality. Surface texturing allows a standard map image showing roads, rivers, and towns, or even aerial photographs to be draped over the DTM image. This results in a highly realistic display, conveying a level of data about the terrain surrounding the aircraft that is not possible with any existing instrumentation.

DTM displays are intended as an aid to increase the pilot's situational awareness during night flying, marginal visual meteorological conditions, or IFR flight using navigation channels. DTM displays can be used on their own or combined with the navigation channel display as required.

Widespread use of DTM displays will see a decrease in the number of accidents caused by a loss of situational awareness.

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