工程CAD中的排图优化算法

Drawing layout optimization algorithmin in engineering CAD

图纸中图块的排版问题直接影响到CAD自动出图系统的出图效果.通过使用表达式描述图块的位置关系,使用关系对表达图块的对齐关系,使用关系组表达图块的缩放关系,建立了分析排图问题的模型.该模型同时考虑了图框大小的变化及标题栏与其他图块之间位置关系的变化.优化过程分为两步,先求出一个最优组合,使得各图块占用可用区域的面积最大,同时要满足各种约束关系;接下来优化高度和宽度两个方向上的图块间距,使得图块在图面上的分布尽可能均匀.在每个图块不超过3个可选比例的前提下,实现在可接受的时间范围内排图效果的最优.实验例证表明,该算法是可靠、有效率的,结果是合理的,能够满足商品化软件的要求.

Drawing layout will directly influence drawing quality in automatic CAD drawing system. Through using expression, relation pairs and relation groups respectively to describe location relation of drawing blocks, alignment relation of drawing blocks and zoom relation of drawing blocks, an analysis model of drawing layout is presented. This model also takes variation of drawing layout area and relation between title bar and other drawing blocks into account. Optimization procedure is divided into two steps： firstly, an optimum combination, which satisfies all restrictions and could make the useable area of drawing blocks as large as possible is obtained： secondly, spaces among blocks could be optimized in both height and width directions to make distribution of drawing blocks on drawing as even as possible. On the precondition that each drawing block has three or less optional ratios, optimum layout effect is achieved in acceptable time. Layout test indicates that this algorithm is reliable, effective and its result is reasonable and could fulfill requirements of commercial applications.