Break-lines show dramatic change in slope for example cliffs, road embankments.
How often is the data updated?
Enhanced DTMs are updated within the same cycle as the orthophotography:
- the enhanced DTM consists of a point file of heights, along with break-lines showing dramatic changes in height
- spot heights are on average 60m apart although the enhanced DTM carries a higher density of data where it is most needed
- can be used in the digital creation of 3D mapping such as slope and aspect maps
- using Geographical Information software, orthophotographs and maps can be draped over a Triangular Irregular Network (TIN) derived from a DTM to create a 3D view of the land surface
- DTM data can also be used in a GI software to create thematic maps, grids and contours
- the enhanced DTM can be used in the electronic process of representing topography in three dimensions for example in a Geographical Information or CAD system.
- the enhanced DTM is Land & Property Service’s most detailed height product
- height analysis
- environmental impact analysis
- sight lines
- wind flow and pollution dispersion
- soil erosion modelling
- flow direction and accumulation
- watershed delineation
- the DTM is created from stereo imagery in the orthophotography production process
- text format
- all height measurements refer to elevation in metres above mean sea level at Belfast Lough
- enhanced DTMs can be used to generate 3D Triangular Irregular Networks (TIN)
- the DTM has 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