If you take a square and look at it from some point in space it looks like a quadrilateral. What are the possible shapes of this quadrilateral?
... haven't Renaissance artists solved this?
It's twopoint perspective. Select two points on the horizon. One set of realworldparallel lines converges at one of the points and the perpendicular set of realworldparallel lines converge at the other point.
The only calculation that needs doing in producing the image of the square on the floor is that when the nearest vertex of the square is not equally distant in the picture from the two vanishing points, one of the nearer sides is shorter than the other, but by how much? After that, it's just connecting the vertices to the vanishing points.

Posted by Charlie
on 20091107 00:51:26 