Digital terrain model of terminology interpretation photogrammetry

DTM (Digital Terrain Model) is a digital representation of terrain fluctuation, which consists of a set of X, Y and Z coordinate data of points obtained by sampling the terrain surface and a set of algorithms that provide continuous description of the ground. Simply put, digital terrain model is a data set organized according to a certain structure, which represents the spatial distribution of terrain features. DTM is the basic data for establishing terrain database, which can be used to make contour map, slope map, thematic map and other graphic products.

The measurement process of DTM is as follows: firstly, according to certain measurement methods (field direct measurement, indoor stereo photography measurement, etc. ), measure the plane position and elevation of a certain number of discrete points in the measurement area, which are called control points (data points or reference points). Then, the control points are used as the network framework, in which a large number of elevation points are interpolated. Of course, the internal broadcast is solved by the computer according to certain calculation formulas and some regular graphics (such as grids). The sum of the plane position and elevation data of control points and interpolation points is the digital ground model of the survey area. The plane position of the landform in the survey area is expressed in digital form, that is, the X and Y coordinates of a point represent the plane position, and the Z coordinates represent the characteristics of the ground.

There are two main data sources of digital terrain model: one is directly taken from the terrain surface, and the other is indirectly taken from the terrain surface simulation model. According to the different data acquisition methods, data sources can be divided into the following four types: (1) from the existing topographic map. The simplest method is to draw contour lines manually on the digital platform. The common method now is to shoot with scanning equipment. (2) Stereo model from photogrammetry. The digital system of most stereo and analytical mapping instruments can obtain data from remote sensing photos. Automatic photogrammetry system uses automatic image correlator to generate high-density elevation points along the scanning section. (3) Field measurement. That is, the plane position and elevation of ground points are directly measured in the field. Generally observed by electronic velocimeter. (4) Direct measurement through remote sensing system. Such as data obtained by radars and laser altimeters carried by aerospace vehicles.