目前有关画法几何学的书籍,大都把直角投影定理作为详述的一节,用以论述空间垂直相交(或垂直相叉)两直线,其中有一条直线,其中有一条直线平行于投影面时的图示规律和图解方法。而未能解决任意平面角的图示和图解问题。本文就此作初步探讨,以期充实画法几何学的基本内容、解决生产实际中任意平面角的图示和图解问题。 At present, most of the books about the geometry of painting have mostly used the right-angle projection theorem as a detailed description to describe two straight lines (or vertical cross) in the space, including a straight line, of which a straight line is parallel to the projection plane The graphic rules and graphical methods. But failed to solve the graphic and graphic problems of any plane angle. This article makes a preliminary discussion on this, with a view to enrich the basic content of the geometry of painting, to solve the graphic and graphic problems of any plane angle in the actual production.