Retard here, can someone explain what am I doing wrong? I am trying to make a cheat sheet for boxes in perspective, starting with isometric view. I am stuck on the first view and I don't understand why the box is wrong. This is 45 degree view so every convex edge should be the same length. I take the upper plane and multiply the lengths by cos(45) because of the viewing angle. I also project it onto the line, which is how I get the distances for the upper rectangle, which seems to be correct. Now, as the lower convex edge is also in a 45 degree angle towards the viewer, it should also be shortened by cos(45). But here the lower edge falls shorter than the other convex edges, which is wrong! Can someone help me?