Abstract 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 objectoriented 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 graphicoriented design.
