Methods Of 3-D Terrain And Creating Of Highway Surface

In the mid-fifties of 20th Century, the scientists of Massachusetts Institute of Technology made the computer used in the photographing survey and put forward a new concept of digital terrain models which is usually called DEM(digital elevation model). Nowadays, DEM which is used in various fields has been developed greatly and is videly used in GIS, too. DEM can be used in three-dimension analysis, simulating continuous distnibuling terrain and prouiding terrain, road design and management analysis.Because the famous GIS software such as ARC/INFO shich can only provide tools of developing three-dimensinal terrain without developing three-dimensional road and management system was very expensive(about 100,000RMB). And the roadway system which is made by Ministry of Communications highway graduate school of Ministry of Communications. Recently, through CAD, the highway graduate school of Ministry of Communicatin formulate a roadway system, which has only simple descriptions of roadway seenery without complex and practical functions of earthwork calculation. So I'll discuss the application of DEM in three-demensional terrain and roadway formation, that is how make analysis through DEM provide scientific effective method for three-dimensional terrain, roadway design and management analysis. Specificly speaking is to present digital elevation data, through the original data and triangle treatment we can get a new data. Then OpenGL will deal with this data to develop a true three-dimensional terrain and three-dimensional road.there are seven parts in this passage. In the first part we can know the DEM defination and tis application in GIS, the development of present three-dimensional terriain and roadway software, and problems to be solved in this article. Some technique points and difficulties including data structure triangle analysis-OpenGL tools are summarized in the 2, 3, 4, 5 parts, and the author's method is stressed, too. The particular introduction of three-dimensional road developtment in the sixth part. And the last part is the brief explanation. Now there are some brief introductions to these questions.Two kinds of DEM data structures are introduced in this article. One is contour line which is widely used in Two-dimentional plane map. The other is regular reseau used in procedure of three-dimensinal terrain development and outputting data. This regular reseau occupies small room and is easily to be searched and managed.Because OpenGL's advantage in protracting regular triangle net. I use square reseau to form, triangle net which is easily stored and managed, too. The regular triangle net can be got through original data on by insent. And then at the base of square reseau, two new triangles are formed by a diagonal.The expression used in this article is Z=1/Q∑QiZi (i=1…n), Z is其中Z为内插点高程, Qi=1/(|X-Xi|+|Y-Yi|),The tool used in this article is OpenGL, which is software meeting jaws including over 300 orders and functions. On the aspect of sunshine and color dealing average peak vector quantitiles are used and it will make the picture smoother.The procedures of developing three-dimensional roadway are as follows: adjusting roadway altitude ->displaying roadway midline ->developing roadway rectangle ->adjusting roadway rectangle ->finding out all the critical points, using different colors to show roadway lines of up-mountains and down-mountains ->developing bucket-wall polygon ->bucket-wall incising triangle pieces displaying the changed bucket-wall polygon ->joining continuous bucket-wall polygon ->roadway incising triangle pieces ->joining incised triangle pieces.