射影即正投影是空间几何的重要内容,在初中的图形的认识和高中数学新教材立体几何的第一节都在知觉感知、操作确认的层面上涉及了许多射影知识,立体几何第二节中在思辨论证和计算的层面上又涉及到了射影内容.许多学生都会错误地认为,一个角在平面上的射影总不会比这个角小,因此 Projective projection is an important part of spatial geometry. The understanding of the graphics in junior high school and the first section of high school mathematics new textual three-dimensional geometry involve many projective perceptions and operational confirmation aspects. In the second section of the solid geometry Projections and calculations also involve projective content, and many students mistakenly assume that a projective angle in a plane will never be smaller than this one, so