I don't visit this site to offend people and I apologise if you took my remark as offensive as all that I was saying that perspective drawing follows simple rules which must be obeyed. To answer "perspective's" question about 2 cubes, you would use measured perspective from a plan view and that is what Larry is stating. I taught technical drawing at a high level for too many years. One area that I found hard to get across to students was how to get the vanishing point of a normal pitched roof building, or an inclined line, this can be done using an auxiliary viewpoint or using a measured elevation. In all there are only 16 simple rules that need to be followed. CAD programmes have taken the calculations out of perspective drawings so the use of rules has realy diminished which means bar simple perspectives none are taught.