基于查表的快速圆弧裁剪算法

A Fast Table-Based Arc Clipping Algorithm

在智能CAD、图形识别与理解等复杂图形应用系统中,由于图元数量多、图元间关系复杂,且系统实时交互响应要求较高,现有圆弧裁剪算法较难满足要求.为此提出一种从2个角度大幅提高圆弧裁剪效率的快速圆弧裁剪算法.首先按圆弧与矩形裁剪窗口的位置关系,通过所在圆、圆弧、分割后的各象限圆弧段与裁剪窗口最多进行三层次适应性相关测试,以较少的操作尽可能多地排除与裁剪窗口不相交的圆弧;其次对剩余的、需通过求交操作完成裁剪的圆弧给出基于查表法的圆弧-直线交点获取方法,避免了复杂的开方操作,可快速获取裁剪结果.在图形识别及智能CAD等应用中的实验结果表明,采用文中算法可较大地提高效率.

Existing arc clipping algorithms are inefficient for many complex real-life applications like intelligent CAD and graphics recognition/understanding systems, due to their large number of graphical primitives, complicated geometrical relations and real-time interaction requirements. A fast arc clipping algorithm is proposed to greatly improve the efficiency in two steps. First, adaptive relational-tests are performed to exclude or reserve those arcs without arc-line intersections as more as possible in three levels： circular boundary boxes, arc boundary boxes and segmented quadrant arc boundary boxes. Second, a fast table-based arc-line intersections retrieval method is proposed to obtain the final clipping results for the rest arcs. Only several times of shift, comparison, addition/ subtraction or multiplication operations are needed to clip any given arc. Experimental results in reallife graphical applications show that the algorithm is very fast and more efficient.