Research Of Key Map Symbolization Algorithm And Design Of Symbolization Engine

Map symbol is an abstract form of the real world. The map symbolizing process is to use the map symbols to represent the geometry element, and to render the map with map symbols based on geometry ingredients. With the popularity of the online map, how to render faster and get better display quality become key issue of the symbolization. Symbolizing is accomplished by Symbolic Rendering Engine, therefor a high efficient Symbolic Rendering Engine is crucial to a Geographic Information System. However, there are only few symbolizing rendering functions in nowadays commercial software, lead to an extremely hard work of the promotion of symbolization on the arithmetic level in the normal commercial software because of their closed source. The main work of this paper is exploring the new symbolizing algorithms and designing symbolizing rendering engine.1.This paper design the subparagraph algorithm for rendering many map symbols which have several subparagraphs. The most difficult symbolizing in map symbol is to paint subparagraph symbols. In order to render them, the algorithm must calculate the coordinates of every subparagraph. This paper analyzes the problems which will be encountered when rendering subparagraph symbols, and designs the algorithm for calculating the coordinates of every subparagraph. Meanwhile, coordinates of subparagraph and location of point symbol which was contained by the subparagraph are calculated at the same time, therefore the calculating time is saved and efficiency is promoted.2.The element relationships also need to be processed while rendering, this paper came up with dealing the problem of these two problems:(1) Appearance of virtual segment in the end of piecewise linear symbolRegarding of the problem of unable to determine the endpoint of line symbol caused by appearance of virtual segment in the end of piecewise linear symbol, the author came up with the idea to add two coordinate points and render with universal segmentation algorithm to realize in an easier way.(2) The intersection of empty part with the solid part of subparagraphsThe intersection of empty part with the solid part of subparagraphs, the area of the intersection of the empty parts of subparagraphs brought the problem of inaccuracy in making sure of the intersection point of the location represented by symbols. To deal with the problem, Bentley-Ottmann algorithm method was used for reference to develop an algorithm of changing the empty part into a solid part or putting a special mark on the intersection.3.Planar symbol rendering algorithm mainly based on Filling Algorithm. Since a conventional Polygon scan line filling algorithm is not efficient, the author came up the scan line filling algorithm based on an edge table sorting elements according to the vertical axis of the sort or the horizontal axis sort. Both of these two algorithms are trying to reduce intersection operation to promote the efficiency.4.On the base of the research of computer cartography and symbolic algorithms, Symbolic Rendering Engine was designed. Through designing symbols class encapsulates the symbol rendering algorithms, Symbolic Engine can easily expand the symbol and algorithm. Symbolic Engine offers abstract data read interface, which can read a variety of symbol files and geographic information files. Additionally, Symbolic Engine designs abstract graphics library call interface, which can extensionally calls multiple graphics library API. After the test, the Symbolic Rendering Engine developed by this paper can render every kind of complex symbol, and process some element relationships with relative fast speed.