What is 4D (DRG, DLG, DOM, DEM) data?

There are different sayings below, but the meanings are very similar. 1. DOM (Digital Orthophoto): The image data generated by using a digital elevation model to scan and process digitized aerial photos and remote sensing images, correct them pixel by pixel, and crop them according to the frame range. Its information is relatively intuitive. It has good interpretability and measurability, and physical geographical and socio-economic information can be directly extracted from it. In SAR image processing, it is often necessary to use DEM data to solve the geometric distortion of slant range imaging caused by RD positioning. Therefore, solving X, Y, Z considers three equations. That is, distance formula, Doppler frequency formula and earth coordinate formula. In other words, DOM requires DEM for secondary processing, and it is also the most advanced product among 4D products. DEM (Digital Elevation Model): A digital collection created through contour lines or aerospace images to express the undulating shape of ground elevation. Currently available are 90m SRTM and 30m Aster GDTM data. The former is obtained using InSAR technology, while the latter is obtained using high-resolution stereo photogrammetry technology. Both similarities require two images, precisely registered. A certain baseline length is required, and the value needs to be within a certain range. The difference is that the former is obtained using the principle of wave coherence, while the latter is the linear equation generated by the linear propagation of light. DEM data is the basic data. DRG (Digital Raster Map): Digital raster map is a digital product in the form of a paper topographic map that can be integrated with DOM and DEM to derive new visual information. This type of data mainly rasterizes existing paper maps and then registers them. Currently, this type of map is rarely used and is mostly replaced by high-resolution images, or the main features are vectorized and represented. Storage, most current GIS software supports this function. DLG (Digital Line Map): Use aerospace images to identify and vectorize the images to establish a vector data set with hierarchical storage of basic geographical elements, including both spatial information and attribute information, which can be used in the space of various professional information systems Positioning basics. This picture is the main form of electronic maps currently left on the Internet such as Google Maps, Baidu Maps, and Sogou Maps. Google Map does the best because it has powerful raster image data and is high-resolution. Therefore, after superimposing vector data, the reflected map image is more intuitive, clear and accurate. 2.

Digital Elevation Model (DEM) is the plane coordinates (X, Y) and elevation (Z) of regular grid points on a certain projection plane (such as Gaussian projection plane) data set. The grid spacing of the DEM should be compatible with its elevation accuracy and form a regular grid series. According to different elevation accuracy, it can be divided into different types. In order to fully reflect the surface morphology, discrete elevation point data can also be added.

Digital Line Graphic (DLG) is a vector data set of existing topographic map elements. It saves the spatial relationship and related attribute information between each element, and comprehensively describes surface targets.

Digital Raster Graphic (DRG) is a raster data file obtained by computer processing of existing paper topographic maps. After each topographic map is scanned and digitized, it is geometrically corrected, content updated and data compressed. The color topographic map should also be color corrected to make the color of each image basically consistent. The digital raster map is consistent in content, geometric accuracy and color with the national basic scale topographic map.

Digital Orthophoto Map (DOM) uses a digital elevation model (DEM) to scan and process digitized aerial photos, and performs projection difference correction and mosaic on a pixel-by-pixel basis. A digital orthophoto data set generated by clipping the national basic scale topographic map frame range. It is an image with both map geometric accuracy and image characteristics. It has the advantages of high precision, rich information, intuitive and real. 3. DOM (Digital Orthophoto Map) is the English abbreviation of Digital Orthophoto Map. It uses a digital elevation model to scan and digitize (or obtain directly digitally) aerial photos (or aerospace images). After digital differential correction, digital Mosaic, and then cut the generated image data set according to the frame range. Digital orthophoto products can be divided into color and black and white according to color.

Main applications: Topographic map revision and testing, production of composite digital products and three-dimensional landscape maps, land use detailed investigation and dynamic monitoring, land use database construction and update, land resources and environmental dynamic monitoring, urban Planning and design, background information on GIS systems, etc.

DEM (Digital Elevation Map) is the English abbreviation of Digital Elevation Model Map. It is data defined on discrete points (rectangles or triangles) in the X and Y domains (or latitude and longitude domains) to express the undulations of the ground in terms of elevation. Set, that is, a data set that specifies the plane coordinates (X, Y) of the mesh points and their elevation coordinates (Z) on the Gaussian projection plane. It is one of the important components of my country's basic geographical information data products.

DEM products are divided into two categories according to the grid type, standard grid DEM and non-standard grid DEM. They are also divided into different levels of products according to their different elevation accuracy. Main applications: highway and railway route selection and design, planning and dynamic monitoring of soil erosion control, mobile communication base station layout design and optimization, mine development design, site selection design of large and medium-sized reservoirs, calculation and analysis of earth excavation and landfill, flood Submerged analysis and more.

DLG (Digital Line Graphics) is the English abbreviation of digital vector map. It is a vector data set of basic geographical information elements on existing topographic maps, and saves the spatial relationship between elements and related attribute information.

Main applications: different professional geographic information systems, detailed land and resources surveys, and vehicle-mounted and airborne GPS navigation information systems.

DRG (Digital Raster Graphics) is the English abbreviation of Digital Raster Map. It is a map graphic data set stored in raster data format and is an important part of my country's basic geographical information data products. Digital raster maps are basically consistent with topographic maps in terms of content, geometric accuracy and specifications, and colors. This product can be formed from simulated maps after scanning, geometric correction, color naturalization, etc., or it can be converted from map graphic data in vector data format.

Main applications: computer map query, background maps of different professional geographic information systems, and base maps for urban planning and design. 4. The maximum accuracy of the map

The shortest distance on the map that the naked eye of a person with normal vision can distinguish is 0.1 mm. Therefore, the actual horizontal length equivalent to 0.1 mm on the map is the most precise limit that can be represented on the map, which is called the maximum accuracy of the scale.

The following table shows the maximum accuracy of the national basic scale topographic map:

Scale 1:10,000 1:25,000 1:50,000 1:100,000 1:250,000 1:50 10,000:1 million

Maximum accuracy (m) 1 2.5 5 10 25 50 100

Digital maps are stored on media such as computer hard drives, floppy disks, optical disks or tapes. Map content is represented by numbers, and special computer software is required to display, read, retrieve, and analyze these numbers.

Digital Raster Map (DRG)

Digital Raster Map (DRG) is a raster digitized product of paper maps. Each map is scanned, assembled, processed, and compressed to form a raster file that is consistent with the map in terms of content, accuracy, and color.

Digital Line Map (DLG)

Digital Line Map (DLG) is a digital map formed in vector data format. This kind of map can layer and overlay spatial information, extract attribute data, query attributes according to vector objects or query vector objects according to attributes. The data is easy to update and edit, create thematic attributes and draw thematic maps, etc.

Digital Elevation Model (DEM)

Digital Elevation Model (DEM) is a digital representation of regional ground elevation. It is a plane coordinate (x, y) and its elevation (z) data set are the core data systems on which geographic information systems rely for analysis. The horizontal interval of DEM can change with different landform types, and it can be divided into different levels of products according to different elevation accuracy.

At present, the world's major developed countries have established digital elevation model systems covering their own countries

Digital Orthophoto (DOM)

Digital Orthophoto (DOM) ) is an image data generated by using a digital elevation model to scan and process digitized aerial photos or remote sensing images (monochrome or color), correct them pixel by pixel, then mosaic the image, and cut the ribbon according to the frame range. Usually a plan with a kilometer grid, outline decoration and annotations.

my country began to establish a national high-precision GPS network in the 1990s. There are 33 national A-level outlets and 818 B-level outlets. The average side length is 50-70 kilometers in the eastern region, 100 kilometers in the central region, and 150-200 kilometers in the western region. These two networks are a new generation of coordinate frameworks established under the International Terrestrial Reference Framework (ITRF), and have established a conversion relationship with my country's astronomical geodetic network, bringing the construction of my country's geodetic coordinate framework to a new level. The last thing I want to say is: DEM data is the most primitive data. With the Tendem interference energy of TerraSAR-X, DEM with 1m resolution will be easier to obtain in the future. Then the next problem is the processing of DEM data. As we all know, DEM is a matrix, a matrix representing height. Equipped with some Image Tie Points, you can know the geographical coordinates corresponding to each point. Such as X, Y of UTM, so now how can we further explore the potential information of DEM data? And how to obtain the data you want according to the requirements of related remote sensing sensors? For example, SAR image simulation based on DEM data. DEM data can also be processed into light and shadow renderings, contours (contour lines), slope, orientation, and profile. . . Wait for a series of data, which lay the foundation for subsequent applications.