Design And Realization Of The System Of Automatic Relief Shading Oriented To Project Application

Generally,the main part of the total information and content expressed by a map is related to relief ,so the rational terrain expression on 2 dimension is greatly significative and important to the information expression and transmission of maps.But the surface of earth is scraggly .How to express the scraggly surface of earth is a difficult and complicated problem.The cartographers proposed several methods to express terrain after long-term research;The main methods are contour lines, altitude tinting,symbol and hill shading. Relief shading has became one of main methods of expression terrain, because it has several advantages as following:1 , Relief shading can make the expressed relief take on greatly three-dimensional vision.So it can make maps attractive and easy to be readed.2 , Relief shading has enough abilities to express most relief.3 , Relief shading itself has artistic property.A lot of maps from many countries were exhibited on the ICA (Internation Cartograph Association) meeting held in Beijing on August 2002.A11 these maps were almost digital maps and relief shading was used by almost 80 percent of these maps.Moreover,several countries ruled that the relief on national maps of fundamental scale must be expressed by relief shading. It is obvious that the relief shading takes on brilliant outlook.This article discussed the origin , development , the fundamental theory and principle of relief shading .Moreover,this article introduced the fundamental knowledge of three-dimensional open graph libray(OpenGL) and the method of automatic relief shading . In addition,the article proposed resolvents for several key problems which prevented the relief shading from being applied widely .These resolvents are:1, proposed and used incremental method to improve the several main processes of automatic relief shading and achived the fleet production of relief shading for enormous data;2, used the method "transform the vector features to bitmap" to settle the problem that concave polygon can not be drawn by OpenGL and achived the precise superposition of relief shading and other vector features in the same coordinate.3 , used the method "magnify model" to settle the problem that mosaics arise when the relief shading maps with other vector features are zoomed in .4, adopted neatly the technique of "Mipmaps"to settle the problem that OpenGL can only mapped the texture of which width and height are all the power of 2 and achived to mapped the texture of arbitrary size to the relief shading. 5, used the method "combination level of detail(LOD) and adjoining blocks" to achieve the fast virtual terrain flying.In the end ,a practical software which can produce relief shading and meet users' manifold requirements was designed and programmed .