DTM and DEM

The Digital Terrain Model (DTM) was originally proposed for the Automatic Design of highways (Miller, 1956 ). Since then, it has been used for the design of various line selection (railway, highway, transmission line), calculation of the area, volume, and slope of various projects, the cross-view judgment between any two points and the drawing of any broken line. It is used to draw contour lines, slope and slope directions, and three-dimensional perspectives in surveying and mapping, and to create a positive image and map repair test. Remote sensing applications can be used as auxiliary data for classification. It is also the basic data of the geographic information system, which can be used for the analysis of the current land use situation, reasonable planning and flood danger forecast. It can be used for military navigation, missile guidance, and electronic sandbox operations. The Research on DTM includes the precision problem, terrain classification, data collection, DTM coarse difference detection, quality control, data compression, DTM application, and the establishment and application of DTM with irregular Triangle network.
From the mathematical point of view, the elevation model is a continuous function of the elevation Z on the plane coordinate X and Y. The Digital Elevation Model (DEM) is only a finite discrete representation of it. The most common expression of an elevation model is the altitude relative to the sea level or the relative height of a reference plane. Therefore, an elevation model is also called a terrain model. In fact, terrain models not only contain elevation attributes, but also other surface morphology attributes, such as slope and slope. A digital terrain model is a digital expression of the information about the terrain surface. It is a digital description with spatial location features and topographic attribute features. When the terrain attribute of a Digital terrain Model is an Elevation, it is called a Digital Elevation Model (DEM ). An elevation is the three-dimensional coordinate of a geographical space. Because the data structure of the traditional geographic information system is two-dimensional, the establishment of the digital elevation model is a necessary supplement. DEM is usually represented by an elevation matrix composed of a regular grid element on the earth's surface. The generalized DEM also includes the digital representation of all the expressions of the ground elevation, such as contour lines and triangular mesh. In geographic information systems, DEM is the basic data for DTM. Other terrain elements can be directly or indirectly exported from DEM, which is called "Derived Data", such as slope and slope.