Introduction to the other two branches of
DTM are digital models represented by a variety of non-ground features, including natural geographic elements, and social economy and humanities related to the ground. Such as soil type, land use type, rock formation depth, land price, commercial advantageous area, etc. In fact, DTM is one of the grid data model. It is the difference between its raster representation of the image. The image is: the image represents a point representing the properties of the entire cell, and in the DTM, the point of the grid only indicates the attribute of the point, and the attribute between the point and the point can be Insert the calculation.
Establishment method
There are a variety of methods for establishing DEM. From the data source and acquisition, it is: (1) directly from the ground measurement, the instrument involved has a horizontal guide rail, the needle, the needle, the relative elevated measuring board, or the GPS, all station, field measurement The high-end instrument; (2) According to the aerospace or aerospace image, obtain the photographic measurement pathway, such as stereo coordinate meter observation and empty three encryption method, analyze the map, digital photogrammetry, etc. (3) Collect from the existing topographic map , Such as grid reading, digital instrument hand tracking and scanner semi-automatic acquisition and then generates DEM, etc. The DEM interpolation method is much, mainly inserted into the whole, plug-in interpolation and insertion in points. The overall insertion model is established by the observation value of all sampling points in the study area. The block interpolation is a block that divides the reference space into a number of sizes, using different functions to each block. Point-by-point interpolation is centered on the intent, define a partial function to fit the surrounding data points, and the range of data points varies with the position of the position, so it is also known as mobile fit. There are two algorithms with rule network structure and irregular network, referred to as TInse.
The currently common algorithm is TiN, and then the DEM is interposed through linear and double linear. The advantages of recording surface fluctuations with regular squares are: (x, y) location information can be implied, no need to serve as a raw data storage due to rule network high-range data, it is easier in data processing. Disadvantages: Data collection is more troublesome, because the grid points are not feature points, and some micro-land may not be recorded. The advantage of TIN structure data: the surface morphology can be described with different levels. Compared to the grid data model, the TIN model can use less space and time more accurately in a particular resolution. More complex. Surface. Special local shape contains a large number of features such as fracture lines, and the TIN model can better take these characteristics.
Form
Data organizations in digital elevation models have a variety of forms, including two types with regular rectangular grids commonly used in land use works.
(1) Rules Rectangular Grid. The rule rectangular grid is on the Gauss bounce platform, in the Z, Y-axis direction, the planar coordinates (Z, Y) and its equation (Z) of the equivalents, and its equation, any point P_ {I, J} The planar coordinates can be calculated based on the row number I, J, and stored in the DEM in the DEM file. The advantage of rectangular grid DEM is that the amount of storage is small and can be compressed, which is easy to use and manage. In the development of agricultural land, due to the smaller range and the terrain changes, the square mesh method is generally used when calculating the floor, so it is applied with a rectangular grid.
(2) irregular triangular network. The irregular triangular network is a DEM represented by an irregular triangular network, usually called DEM or TIN (Triangulate Irregular Network), because each point constituting TiN is raw data, avoiding the loss of interpolation accuracy, so TIN can be better Estimated the characteristics of the geomorphology, line, indicating that the complex terrain is accurate than the rectangular grid. However, TiN has a large amount of data, except for the topology of the network point connection, which is generally applied to a larger range of aerosol measurement.
Data Source
Data Sources of Digital Elevation Models Mainly include:
photogrammetry, ground measurement, existing topographic diagram, existing Extract in the DEM library. For local earthwork, it is obviously in economical, unless it is economically inadvertent, unless it is economically inadvertent, and is not suitable for the grid spacing, unless the original information is applied). Therefore, in the actual work, the existing large-scale topographic graph scan vectorization is mainly taken, or the three-dimensional coordinates of the measuring point are directly measured by a full station, the rangefinder + electronic plate.
Resolution
DEM resolution is an important indicator of DEM portraying the accuracy of the terrain, and is also a major influencing factor determined by its scope of use. The resolution of the DEM refers to the length of the smallest cell. Because DEM is discrete data, the (x, y) coordinates are actually a small square, and each small square identifies its elevation. This small square is the resolution of the DEM. The smaller the resolution value, the higher the resolution, the more precise the shape of the portrait, and the data volume is also growing in geometry. So the production and selection of DEMs should be balanced between accuracy and data. At present, my country has completed the construction of a DEM of 1:50 000 topographic maps.
Purpose
Due to DEM, it is the ground elevation information, which is in mapping, hydrological, weather, geomorphology, geological, soil, engineering construction, communication, military construction, national economy and national defense construction. And a wide range of applications in the field of humanities and natural sciences. As in engineering construction, it can be used for earth equivalent calculations, visual analysis, etc. In terms of flood control and disaster reduction, DEM is based on hydrological analysis such as Huishui analysis, water system network analysis, rainfall analysis, storage and changing calculation, submergence analysis, etc. On wireless communication, the base station analysis of the cellular phone can be used.
Product case
National provinces and cities DEM data products are one of the land resource data products launched by geographical national conditions. Based on the TIN algorithm, the DEM data is built on the DEM data, and the data accuracy is 30m, 90m, 1km, and the data quality is good, and the user's specific needs can be satisfied.
The electronic elevation (rendering) data products in various provinces and municipalities across the country.