| A digital terrain model, also known as a digital | | | | can be related to a specific location. This |
| elevation model, is a digitally-created | | | | information can then be turned into a digital |
| representation of ground topography and terrain. | | | | contour map or terrain model, which turns the |
| Although maps depicting topographical information | | | | raw data into a model enabling the viewer to |
| have been produced for hundreds of years, it is | | | | "visualize" the landscape in a virtual manner. |
| only recently that such elevation data has been | | | | Unlike contour maps, DTMs provide continuous |
| collected in such a precise digital form as to allow | | | | elevation information. Contour maps, on the other |
| the creation of digital models. | | | | hand, connect points that are equal in elevation, |
| The digital elevation model can be used to model | | | | but do not generally provide elevation data for |
| water flow or other movements, for example to | | | | intermediate points. A digital terrain model also |
| run simulated avalanches or landslides, or for | | | | differs from a contour map in its visual |
| land-use studies, transportation system planning, | | | | appearance. A digital terrain map appears 3D; in |
| and geological applications. Other uses include the | | | | many cases, "fly throughs" or similar programs |
| creation of physical raised-relief maps, flight | | | | allow the user to manipulate the map to view all |
| simulator programs, or other visualization and | | | | areas and angles of the terrain. |
| modeling applications. Digital terrain models are also | | | | A digital terrain model usually includes only the |
| incorporated into geographic information systems. | | | | Earth's surface, excluding vegetation as well as |
| There are many ways to obtain the information | | | | buildings or other man-made features. This is |
| shown in a digital terrain map. Often this data is | | | | sometimes referred to as a bare-earth model. A |
| obtained using remote sensing equipment rather | | | | Digital Surface Model, on the other hand, shows |
| than direct surveying methods. Radar satellites are | | | | such features in addition to the natural terrain. |
| often used for models of large areas of terrain. | | | | The problem with some surveying methods used |
| Though these satellites often only have a | | | | to create these models, such as radar, is that |
| resolution of about ten meters, they can obtain | | | | they reflect the highest elevation point on a given |
| information on an area tens of miles wide in a | | | | location, whether this is the top of a tree or |
| single pass. There are other methods, too. A pair | | | | building or bare ground. |
| of images acquired with different angles taken | | | | A free low-resolution digital elevation model of the |
| from an airplane or satellite can be used to infer | | | | earth, known as GTPPO30, is available. A much |
| the terrain. The first digital terrain models using | | | | higher quality DEM is available from the ASTER |
| this method were created in 1986 for a large | | | | instrument of the Terra satellite. The US |
| portion of the planet using data from the SPOT 1 | | | | Geological Survey also provides the National |
| satellite. | | | | Elevation Dataset, seamless elevation data for the |
| In many cases, digital terrain models are | | | | contiguous United States. Free digital elevation |
| generated from contour maps, often those that | | | | models can also be found for Mars. However, for |
| have been produced by direct surveying of the | | | | a specific application, purpose-created DEM, DTM, |
| land surface. Contour line data is obtained by | | | | or Digital Surface Models may be required. These |
| various surveying methods, including LIDAR, | | | | models are very accurate, and are usually |
| Doppler radar, Theodolite or total station | | | | requested by public agencies or large corporations. |
| surveying equipment. Using GPS, elevation data | | | | |