Using Internet Resources for Teaching - Perspective (art)

After a request from my wife I started looking for teaching resources to help with drawing in perspective.  I thought this type of subject which is not simple but does follow rules, would be ideal for internet and I was right.  There is a lot of material.

Sources for slide presentations includes slideshare and slideboom, and of course there was some very useful material on YouTube.  Strangely enough Wikipedia was not so useful on this occasion, which is unusual.  The above picture is one of my own. The following is the shortest useful presentation I found on YouTube.