Products produced by photogrammetry? What are DSM, DEM, DOM and DLG? What is a point cloud?

DOM (Digital Orthophoto Map): The scanned digital aerial photos and remote sensing images are corrected pixel by pixel through the digital elevation model, and the generated image data is cut according to the scope of the map. Its information is intuitive, with good interpretability and measurability, from which physical geography and socio-economic information can be directly extracted. In SAR image processing, DEM data is often used to solve the geometric distortion of slant range imaging caused by RD positioning. Therefore, three equations should be considered when solving x, y, z, y and z, namely, the distance formula, the Doppler frequency formula and the earth coordinate formula. In other words, DOM needs DEM for secondary processing, and it is also the highest-end product in 4D products. DEM (Digital Elevation Model): A set of numbers established by contour lines or aerial images to express the undulating form of ground elevation. Currently, 90m SRTM and 30m Aster GDTM data are available. The former is obtained by InSAR technology, and the latter is a high-resolution stereo photogrammetry technology. The similarity between them requires two images and accurate registration. It is necessary to have a certain baseline length and take a certain range of values. The difference is that the former is obtained by using the principle of wave coherence, and the latter is the * * * line equation generated by the straight-line propagation of light. DEM data is the basic data. DRG (Digital Grid Map): Digital Grid Map is a digital product in the form of paper topographic map grid, which can be integrated with DOM and DEM to derive new visual information. This kind of data mainly rasterizes the existing paper map and then registers it. At present, this kind of map is rarely used, and it is mostly replaced by high-resolution images, or the main features are vectorized and stored. At present, most GIS software supports this function. DLG (Digital Line Drawing): Through the recognition and vectorization of space images, the vector data set of layered storage of basic geographical elements is established, which contains both spatial information and attribute information, and can be used as the spatial positioning basis of various professional information systems. This kind of map is the main form of electronic map left over from the Internet at present, such as Google Map, Baidu Map and sogou Map. Google Maps does the best because it has powerful raster image data and high resolution. Therefore, after the vector data is superimposed, the reflected map image is more intuitive, clear and accurate.