Use of digital terrain model in road design

Later, further data were provided by the European Remote-Sensing Satellite (ERS) using the same method, the Shuttle Radar Topography Mission using single-pass SAR and the ASTER instrumentation on the Terra satellite using double-pass stereo pairs. In 1986, the SPOT 1 satellite provided the first usable elevation data for a sizable portion of the planet's landmass, using two-passes stereoscopic correlation. Alternatively, other kinds of stereoscopic pairs can be employed using the digital image correlation method, where two optical images acquired with different angles taken from the same pass of an airplane or an Earth Observation Satellite (such as the HRS instrument of SPOT5 or the VNIR band of ASTER). One powerful technique for generating digital elevation models is interferometric synthetic aperture radar: two passes of a radar satellite (such as RADARSAT-1), or a single pass if the satellite is equipped with two antennas (like the SRTM instrumentation), suffice to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters. Дigital Elevation Model of the United States using shade relief derived from slope data Дigital elevation models may be prepared in a number of ways, but they are frequently obtained by remote sensing rather than direct survey. One cannot describe continuously varying terrain using only three discrete variables, so all descriptions are necessarily approximations of reality. Geometry, however, has only three terms: point, line, and area. Prominent terrain features can be verbally described using many terms, such as smooth slope, cliff, saddle and so on. The systematic part is best represented by lines and typical single points. The systematic part of the terrain surface is characterized either by sharp cracks in the terrain, such as the top or bottom of a road cut, or by characteristic points such as spot depression and spot height. It is usual to use a network that creates sloping triangles or regular quadrants. It would take an endless number of points to describe exactly the random terrain shapes, but these can be described in practice with a network of points. The random (stochastic) elements are the continuous surfaces with continuously varying relief.

The terrain surface can be described as compromising of two different elements random and systematic. DEMs are used often in geographic information systems, and are the most common basis for digitally-produced relief maps. DEMs are commonly built using remote sensing techniques, but they may also be built from land surveying. While the term can be used for any representation of terrain as GIS data, it is generally restricted to the use of a raster grid of elevation values.

It is also widely known as a digital terrain model ( DTM). Topography of the Andes from a digital elevation modelДЄ digital elevation model ( DEM) is a digital representation of ground surface topography or terrain.

Use of digital terrain model in road design