Enhanced Digital Terrain Model height data

An Enhanced Digital Terrain Model (DTM) is a digital file showing break-lines and spot heights. Break-lines show changes in slope for cliffs and road embankments. An enhanced DTM provides a detailed representation of the topographical variations in the earth's surface.

Updating the data

Enhanced DTMs are updated within the same cycle as the orthophotography:

Information about the enhanced DTM

The enhanced DTM has a point file of heights, along with break-lines showing differences in height.  The enhanced DTM data features are:

  • suitable for digital creation of 3D mapping such as slope and aspect maps
  • using Geographical Information software, orthophotographs and maps, it can be draped over a Triangular Irregular Network (TIN) derived from a DTM to create a 3D view of the land surface
  • can abe used in a GI software to create thematic maps, grids and contours
  • can be used in the electronic process of representing topography in three dimensions for example in a Geographical Information or CAD system

Where to use an enhanced DTM

An enhanced DTM is suitable for applications in:

  • planning
  • engineering
  • visualisation
  • height analysis
  • environmental impact analysis
  • sight lines
  • wind flow and pollution dispersion
  • soil erosion modelling
  • flow direction and accumulation
  • watershed delineation

Technical information

The enhanced DTM is created from stereo imagery in the orthophotography production process.  It has:

  • DXF format
  • 60m point spacing with break-lines for notable changes in slope
  • all height measurements in metres mean above sea level at Belfast Lough
  • an accuracy of 1.0m RMSE (root means square error) - 65 per cent of data has an accuracy of 1.0m, 90 per cent has an accuracy of 2.0m, and 99 per cent of the data has an accuracy of 3.0m

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