3D Representation Theory And Technology Of Geographic Information

Based on the deep study of 2D(two dimensions) digital topographic map and DEM(digital elevation model), the author puts forward the concept of 3D(three dimensions) digital topographic map. In 3D digital topographic map, configuration of the ground and features on earth are all 3D spatial objects, their spatial position and cubic shape are represented with 3D discrete points. 3D digital topographic map has the following characteristics:â‘ It can show not only the configuration of the ground, but also the cubic shape of features on earth;â‘¡3D digital topographic map is vector map, in which relief and features are represented with 3D discrete points, the planimetric position and size of features and the elevation or height are all showed in scale 1:1;â‘¢3D digital topographic map is usually applied in small area , it is large scale or high resolution(e.g., 1:500or 0.05m,1:1000 or 0.1m,1:2000 or 0.2m), so spatial geographic information can be represented more accurately and more integrally.â‘£3D digital topographic map exists only in digital or electronic , it can not be presented in paper. 3D digital topographic map is actually the 3D spatial data display and visualization based on abstract symbol, it unfolds geographic landscape before user with cubic modeling technique, so it can accurately reflect the spatial characteristic of geographic entity, we can acquire not only the planimetric relationship among spatial entities ,but also elevation of the earth's surface and height of surface features from 3D digital topographic map. 3D digital topographic map greatly promotes the spatial expression ability and the measurement level of digital map, further promotes the spatial cognitive ability and the spatial analysis ability. 3D digital topographic map can be used in a variety of projects, especially in complex terrain region, 3D digital topographic map is very useful. Many operations can be made in 3D digital topographic map, for example, querying 3D coordinates(planimetric coordinates and elevation)of arbitrary points; measuring or querying the slope distance, the horizontal distance, elevation difference, slope, horizontal azimuth and spatial azimuth between two points; computing or querying the spatial length of line features such as electrical wire, highway, railroad and irrigation ditch; 3D analysis such as intervisibility analysis between two spatial points and lighting area analysis etc.. 3D digital topographic map makes many projects plan and design more simple and speedy. Furthermore, based on 3D digital topographic map, we can make more accurate 3D image map, as well as make 3D spatial data visualized. 3D digital topographic map is the data source and technique base of virtual reality technique and 3D GIS(geographic information system), which are the cores of 3D spatial data display and management technique, study on 3D digital topographic map will powerfully promote the development of virtual reality technique and 3D GIS. In this paper, we mainly discuss the concepts, core theories and technology of 3D digital topographic map, many problems need deep study such as data capture, graphic processing, data management, cartography synthesizing and 3D display etc., based on these studies, we will put forward a set of methods and design symbol system of feature representation in 3D digital topographic map.