中文摘要：

为解决在AutoCAD中只能用短直线拟合表示回旋线、计算和绘制效率低、不能实现修改和查询等问题，采用改进的级数展开积分法保证计算精度和效率；运用ObjectARX自定义实体和面向对象编程技术，从曲线基类派生自定义回旋线类；论述了自定义回旋线的绘制、修改、查询、存储和拖动的程序实现方法，讨论了精度控制方法。实验结果表明，该方法能高效的开发自定义回旋线程序，解决短直线拟合所产生的问题，实现面向图形的设计。

英文摘要：

In AutoCAD, clothoid can be fitted only by short straight lines, which cannot be modified and queried, and this method is inefficient in calculation and drawing. The series expansion integration method is improved to ensure the accuracy and efficiency of calculation. With the techniques of ObjectARX custom entity and objectoriented programming, the custom clothoid class is derived from the curve base class. The programming methods for drawing, modifying, querying, storing and dragging of the custom clothoid are stressed and the accuracy control method is discussed. The experimental results show that the above methods can develop the programs for custom clothoid efficiently, which can solve the problems caused by fitting and implement the graphicoriented design.