I am working with a problem to try to translate a projection onto a plane. It is in the simple case, a square projected onto a surface where only two degrees of rotation are allowed. This should result in a trapezoid but I can not see how the cartesian points are being determined by the equations below. I can't seem to understand how the two equations below for Xcouch and Ycouch, determine the four vertices of the trapezoid.
It has been a long time for me working with these geometric equations. Any help would be appreciated. I hope the inserted graphic is legible.
Thanks in advance. Glen Naekel.

It has been a long time for me working with these geometric equations. Any help would be appreciated. I hope the inserted graphic is legible.
Thanks in advance. Glen Naekel.
