| When handling 2D-CAD drafting which contains a large number of data, 2D-CAD software——specially domestic 2D-CAD software——always has a significant performance degradation. This paper presents a multi-line simplification algorithm to deal with this problem. When refreshing the screen, the algorithm reduces the amount of data to display on the screen with the promise of the quality of graphic display. The algorithm can improve the response speed of 2D-CAD significantly.Good algorithm needs appropriate data structures. This paper attempts to organize the data in a 2D-CAD drafting by spatial data structure, and finally selects R-Tree. As a dynamic data structure, R-Tree allows elements overlap each other, and this feature makes it suitable for the geographic information systems and CAD systems. The multi-line simplification algorithm demonstrated in this paper is based on R-Tree.Firstly, the algorithm"Tiny Node Simplification"is present: when transform the minimum boundary box of an R-Tree node to screen coordinates, if its maximum side length is not more than one pixel, draw a point on the screen, and ignore the all elements which are the children of the node.Secondly, with the naturally data accumulation effect of R-Tree, the algorithm"Multi-line Simplification by Covering and Splicing"is presented. Based on the"tiny node simplification"method, the algorithm tries to achieve the display of several lines by only one line display process. The multi-line simplification algorithm is composed by"Tiny Node Simplification"and"Multi-line Simplification by Covering and Splicing".Thirdly, to make multi-line simplification algorithm works better, this paper presents a new framework for the display module of 2D-CAD, and describes the working mechanism of the framework as well as advantages.Finally, the paper tests the effect of the algorithm by experiment. The result shows that the"Multi-line simplification"algorithm can play an effective role on the improvement of response speed for 2D-CAD. |
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