This type of sidewalk chalk drawings are done by Julian Beever, the guy on the diving board in this picture. They are all 2d but look 3d from the right angle. More can be seen at http://users.skynet.be/J.Beever/pave.html . I covered this in an art class in college so I thought I would all share it with you. I would love to see a giant insulator rising out of the pavement.