在平面内有一个已知图形G~*和一条已知直线l与G~*相交(即它们有公共点),现将这个平面沿l翻折成一个二面角α-l-β,使其平面角等于已知角θ.试问:怎样画出这个翻折图形的直观图呢?本文谈谈这类直观图的斜二测画法,供参考.(一)首先讨论:怎样画出上述问题中的二面角α-l-β的直观图?(1)设θ=90°.这时α-l-β是直二面角,它的直观图的斜二测画法是众所周知的.按习惯,总是把它的一个面β置于竖直位置,并且面β正对着看图者.画直观图时,作一个平行 In the plane there is a known pattern G~* and a known straight line l intersects with G~* (ie, they have common points). Now fold the plane along l into a dihedral angle α-l-β so that The plane angle is equal to the known angle θ. How do you draw a visual plot of this folded graph? This article talks about the oblique plot method of this type of intuitive graph for reference. (A) First discuss: how to draw the above The dihedral angle α-l-β in the question is a visual map of (1) Let θ=90°. At this time, α-l-β is a straight dihedral angle. The oblique digraph method of its intuitive graph is well known. By convention, always put one of its faces, β, in an upright position and face β is facing the viewer. When drawing an intuitive picture, make a parallel