1. 4D products
With the combination and continuous development of mapping technology and computer technology, maps are not limited to previous models. Modern digital maps are mainly composed of DOM, DEM, DRG, DLG and composite models.
Mapping 4D products mainly include DOM, DEM, DRG and DLG.
What is DOM? In mapping Aerial photography it means digital orthophoto.
DOM (digital orthophotograph) refers to the image data generated by using aerial photos and Remote sensing images, which are edited according to the scope of the map after the pixel correction. Its information is rich and intuitive, with good legibility and measurability, from which the physical geography and social economy information can be extracted directly.
DEM (digital elevation model) : the digital elevation model is a set of Numbers expressing the undulations of the ground. It can be used to make perspective drawing and section drawing, calculate the engineering earth and stone, count the surface coverage area, and analyze the geomorphologic form related to elevation, access condition and flood area.
DRG (digital raster map) : digital raster maps are digital products in the raster form of paper topographic maps. It can be used as background and related to other spatial information for data collection, evaluation and update, and can be integrated with DOM and DEM to derive new visual information.
DLG: vector data set stored in layers of underlying geographic elements on existing topographic maps. Digital line drawing includes both spatial information and attribute information, which can be used for construction planning, resource management, investment environment analysis and other aspects, as well as as the spatial positioning basis of various professional information systems such as population, resources, environment, transportation and public security.
2. DOM collection method and production process
We already know what DOM means. So how does DOM(digital orthophoto graph) collect data and produce it?
Digital orthophoto image is a digital orthophoto data set generated by using digital elevation model (DEM) to correct the projection error of scanned digital aerial image or satellite image data collected at high altitude and inlay them pixel by pixel.
For aerial photos, the full digital photography system is used to restore the photographic attitude during Aerial photography, establish a three-dimensional model, detect, edit and generate DEM in the system, and finally produce DOM with high accuracy.
For satellite image data, existing DEM data can be used to generate DOM data through single-chip digital differentiation correction.
(1) DOM production process
Before generating DOM, relevant data should be collected, that is, data preparation stage, including original digital aerial photos, analytical aerial triangulation results, DEM results, etc.
After the completion of data preparation, in software, L1 level image of each strip correcting, obtain ChanHang belt are orthographic images (L2), and examine the orthogonal projection of the corrected as if there is a problem such as deformation, distortion, ghosting, fuzzy, an analysis of the causes are not ideal area, repeatedly modified until the generate qualified images.
Samples were selected based on experience. The samples required features with comprehensive elements and rich color saturation, including residential areas, roads, rivers, fields and other features. The application software, according to the sample of the corrected single strip image of the overall uniform light uniform color, make the whole area of the orthophoto tone consistent. For the deformation, loss of features, uneven color transition and other problems in the image, the software is used to repair the image.
After the above work is completed, the image results are segmented and clipped in DOM by software, and the required scale is used to generate a standard map for 20m of external expansion of the coordinate system. After framing clipping, ensure that the raster coordinates of the first pixel in the upper-left corner of each DOM are located at the center of the pixel, and that the value of the planar coordinate system of the DOM grid should be an integer multiple of the pixel resolution.
(2) DOM quality check
Once you've finished making the DOM, you need to check the quality of the DOM. From the mathematical basis of DOM results, framing and numbering, resolution, data coverage, accuracy, image quality and other aspects, the image results were 100% checked, and corresponding inspection records were formed.
Note that when DOM quality checks:
① DOM mathematical foundation should be correct, within the scope of the image should be no loopholes;
②the DOM should have clear images, moderate contrast, even color and tone, with continuous, seamless and visual consistency;
③After inlaid DOM, there should be no obvious change in gray level or obvious inlaid marks near the inlaid line;
④the features and landforms on the digital orthophoto image should be true, without distortion, noise, cloud shadow and other defects;
⑤the overall appearance of digital orthophoto images should be neat and beautiful;
⑥The edge difference on the image data does not produce the visual difference of integrity and distinctiveness
Application of DOM in various industries
DOM has the advantages of high precision, rich information, intuitive and real, and can be used as background control information to evaluate the accuracy, realism and integrity of other data. It can aggregate natural resources and social development information, and provide reliable basis for disaster prevention and public facility construction planning. It can also extract and derive new information from it to realize the revision and update of the map.
In the field of urban mapping, DOM has been widely used in urban planning and design, transportation planning and design, survey of urban green coverage rate, survey of urban built-up area development, planning of scenic spots and historic interest areas, survey of urban development and ecological environment, and research on sustainable development, and achieved significant social and economic benefits.
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