Ask Mr. Perspective

Bruce Conkle of Portland, Oregon, writes:

Sorry to bother you and I won’t be bothered if you don’t answer, but I am trying to figure out the back corner of a box in 3 point perspective. If I draw a line from the top corner to the nadir, and one off to the left vp and one to the right vp, they don’t quite match up at one spot. Any tips for this? I have been making my students draw a table and chair in 3 point perspective, and this issue keeps coming up…

I asked my students to begin by drawing a box and then making each gravity line a leg and then erasing the bottom edge of the box to reveal a table shape. But one problem keeps arising, and that is placing the back leg/foot of the table. I have attached a sketch that illustrates the problem in the original box form.

The issue I am having is trouble finding the back corner of the  box. I tried to find it by taking lines back to each of the vanishing points, but instead of lining up in one spot to determine the corner, I get a triangle.

Bruce,

Perspective is an approximate art when practiced with relatively clumsy tools like rulers and pencils, and especially at a small scale it is easy for small discrepancies to magnify into major misalignments. My method when I run into lines that don’t meet is to keep drawing new ones off the points I have, until l come up with a shape that pretty much fits. With a bit of extra drawing, I was able to arrive at a bottom rectangle that seems to line up with your vanishing points pretty well. A useful check would be to add a diagonal v.p. on the top horizon- that will keep the shape of both rectangles consistent. I hope that helps.