Digital elevation model course notes
Chapter 2 Data acquisition of digital elevation model
DEM data includes two information of plane position and elevation data. What data source and corresponding process depending on the availability of these source data, on the other hand, depending on the resolution, accuracy requirements, number of quantity, and technical conditions depending on the DEM.
Data source of the first number of digital elevation models
Image, topographic map, ground itself, other data sources
Second section data acquisition method
Existing photogrammetry sampling methods involve DEM data acquisition including contour line method, rule grid, selection sampling method, gradual sampling method, cross-sectional method, mixed sampling method.
Get data from existing topographics, hand-held tracking digitization, scan data, and screen digitization,
The theoretical contact of the third quarter
If the sampling of a function g (x) is subjected to a sampling of the DX, the function of the function above 1 / (2x) will not be recovered by repeating the sampling data.
There are three different views of the sampling method: based on the sampling of statistical views, based on the sampling of geometry, based on the sampling of the characteristics.
Statistical perspective: The DEM surface can be considered as a specific set of points (or sampling space), and there are two methods of random and system for collection.
Geometry point of view: The surface of the DEM can be expressed by geometry, which can be divided into rules and irregularities according to their own properties, while the former can be subtracted into one-dimensional structure and two-dimensional structure. The irregular structure used for data points sampling is typically an irregular triangle or polygon. For the rule structure. If a rule is exhibited in one dimensional space, the corresponding sampling method is called a cross-sectional method or the like, and the two-dimensional rule structure is usually square or rectangular, or a series of continuous equilateral triangles, six sides Shape or other geometric graphics.
Based on feature: The DEM surface consists of a limited number of points, and the information contained in each point may vary depending on the position of the DEM surface. In this view, the point on the surface of the model can be studied, and the points on the surface of all DEMs can be composed of feature points and lines. The other set consists of a random point. The feature point refers to the topic of the top, such as the top of the mountain, such as the top of the mountain, and the footprint, such as the characteristic point, such as the ridgeline, valley line, fracture line, Construction line, etc. Features point, line not only contains its own coordinate information, but also implies some information of its own surrounding features, more importantly, if only feature points, lines are collected for the entire surface, the main features of the surface can still be obtained. In this sense, the sampling method can be divided into two methods of selecting sampling and non-selective sampling.
