I have amassed a number of interesting props with which to teach the concepts of linear perspective, including this Brownie camera. I use wrapped gifts, cereal boxes; toy chairs and houses, spice boxes, and a host of interesting rectangular vases.
When I teach linear perspective; it can get a little "mathy" which is not a problem for me as that is my avocation. However, turns out my challenge is to discern the line (pun intended) between too mathy and just right when describing the process to my painting students.
When my teen-aged daughter has a day off which coincides with my painting class, she loves to accompany me; paint, and sometimes advise. Recently, she said to me after class, 'Mom, you had them all at "parallel", lost a couple at "perpendicular", but you have to draw the line at "orthogonal"! ' So, there's the virtual line... somewhere between parallel and perpendicular. See it? I do, now.