Digital elevation models (DEMs) are three-dimensional maps of an areaâs topographical features or surface terrain. They differ from other types of digital terrain models (DTMs) in that they offer continuous elevation data of the various locations included in a mapped area. Thus, terrain maps like contour line maps or topographical maps might be referred to as DTMs but not DEMs. Techniques for creating digital terrain models include remote sensing techniques like satellite and plane imaging, as well as the more traditional method of direct land surveying. DEMs today are used in geographic information systems (GIS) and in consumer and industrial electronic devices and products, like GPS maps and digital location based services offered by cellphone providers. Specific MethodsThe most powerful technique for creating digital elevation models is called the interferometric synthetic aperture radar technique. This is where orbiting satellites take radar images over the course of two passes over the terrain that is being mapped. This is sufficient to produce a DEM map of ten kilometers per side and with a resolution of 10-meters. Another common, if not as powerful method, is called digital image correlation, whereby two optical images taken by a plane or earth observation satellite are combined. The two pictures, taken from different angles, produce a more complete data set for each portion of the terrain being mapped. The first set of usable elevation data for a large portion of the earthâs continental surface was procured by the earth observation satellite SPOT 1 in 1986 using this method. The traditional method of direct land survey is not as common when it comes to digital elevation models as the two discussed above. However, land survey is still used for mapping mountainous regions, which are not as accurately mapped using remote sensing methods. Some of the specific fields in which DEMs are being used today include flight simulators, GPS devices, precision farming, advanced driver assistance systems and intelligent transportations systems. This last field has probably generated the most activity and speculations. With the help of advanced 3D elevation mapping it might be possible to make vehicles more autonomous even outside of the controlled city streets.
To learn more about digital terrain maps and the digital elevation model please visit http://www.intermap.com.
Ryan Frank is a 23 year writer and blogger living in San Diego, CA.
