Digital terrain models are three dimensional digital images of ground terrain. Digital terrain models can be used for the creation of relief maps, physical models and for aerial photography to aid with correcting the geometry of the photographs. They are usually built using satellite and other remote sensing techniques.
A digital terrain model can be represented by a grid of squares (raster) or as a series of irregularly shaped triangles (Triangular Irregular Network).
Terrain maps are created by land surveying and remote sensing techniques which help to reveal the bare ground by digitally removing features like forests and cities from the mapped area. This is done through manual editing, proprietary software, and quality control processes which obtain altitudes based on measurements from the original data.
Digital terrain models are often used in the topographical mapping development process. Digital terrain modeling also supports digital mapping, agricultural, and flood applications among others.
The DTM terrains can be used electronically to create 3D terrain models representing topography, including slope and aspect maps.
Using topographic GIS data, orthophotographs and maps can be draped over a Triangular irregular network created from a DTM to create a 3D image. DTM data can also be used to create maps, grids and contours.
Digital terrain modeling is used by a number of industries including the construction industry where they are used to create elevation models. Digital data such as maps and photographs are draped over the elevation models to give a 3D view of the ground surface. 3D architectural models of future developments can be added to the data to properly assess planning and environmental impact.
DTMs are also used for various analytical applications. As an example, insurance companies use DTM terrains to carry out floodplain analysis, to identify which areas have high and low flooding risk, when setting premiums.
Digital terrain modeling is also used for physical geography, geomorphology, physical geodesy, gravimetry, gravity measurement, satellite imagery and aerial photography.
Height information is integral to DTM. The quality of a DTM is dependent on the grid interval and data source from which it is created.
A DTM can be visualized through 3D-wire mesh models which use colored height columns. Cross sections, contour lines, volume calculation and slope models can also be derived from the DTM topographical mappings. DTM is also crucial to the production of geo-referenced aerial photos.
In order to calculate a DTM, a sufficient amount of height information is necessary. This can be gathered from laser scanner mapping or from photogrammetric restoration. First a cloud of heights is generated by software which is done simultaneously in multiple images through automated elevation collection. The results are then checked by the operator and corrected as necessary. Elevation points on vegetation and man-made features can then be removed and the gaps filled. The final DTM is then created.
Aside from the previously specified usages, DTM are also used in flight simulation, battlefield training and for digital earth mapping such as Google Earth and Microsoft's Virtual Earth.