Digital Terrain Model (DTM, Digital Terrain Model) was originally proposed for automatic design of the highway (Miller, 1956). Thereafter, it is used for the design of various line lines (rails, roads, power lines) and the area, volume, slope calculation of various projects, and any two points between the two points and any section drawing. In the measuring and mapping, it is used to draw contours, slope slope, and a three-dimensional perspective, making a positive shot image map, and a map of the map. As a classified auxiliary data in remote sensing applications. It is still the basic data of the geographic information system, and can be used for analysis of land use status, reasonable planning and flood danger forecasting. In military can be used for navigation and missile guidance, combat electronic sandbox, etc. Research on DTM includes the accuracy of DTM, terrain classification, data acquisition, DTM thickness detection, quality control, data compression, DTM application, and irregular triangular network DTM establishment and application.
From the perspective of mathematics, the elevation model is a continuous function of the two arguments of the plane coordinate X, Y, the digital elevation model (DEM) is just a limited discrete representation. The most common expression of the elevation model is the alversion model is also a terrain model with respect to the altitude height of the sea level, or a relative height of a reference plane. In fact, the terrain model not only contains elevation properties, but also other surface morphological properties such as slope, slope, etc. The digital terrain model is a digital expression of the terrain surface morphid attribute information, which is a digital description with spatial location features and terrain properties. The topographic properties in the digital terrain model are elevated as a digital elevation model (DEM). The elevation is the third dimension coordinate in geospatial. Since the data structure of the traditional geographic information system is two-dimensional, the establishment of a digital elevation model is a necessary supplement. DEM usually uses an elevation matrix constituted by the land rules grid unit, and the broad DEM also includes a digital representation of all expressions such as contour lines and triangular webs. In the geographic information system, DEM is the basic data of the DTM, and other terrain elements can be exported directly or indirectly from DEM, called "derived data", such as slope, slope.
