Everything makes sense to me except for "Establish depth at first square foot." How am I suppose to do that accurately? If I put the line too high or too low it will turn out to be a rectangle.
Thank you for posting this, that picture helped me understand perspective better! Initially, i was about to say that there's no precise way to calculate the square sizes, my teacher taught me always to estimate the square's depth, but then i figured out what the artist meant. From what i can tell, the diagonal vanishing point is needed.http://i17.photobucket.com/albums/b66/homeworld4/squares.jpg
After you have the diagonal, you can just put the horizontal lines through each intersection, the way the artist shows. Of course, my squares are very distorted, especially to the bottom, i'm not sure why they came out like that. Probably because the original artist put his diagonal vp farther to the left than me. I have no idea how to incorporate this into two-point perspective, though.