Hi,
the reason I’m asking - it is a well known fact that to draw a perfect circle in perspective - it has to be drawn inside a perfect square. And if your square is actually a rectangle rather than a square - you’ll end up drawing an ellipse in perspective and not a circle…
So, the question is - how do I know that I’m drawing a perfect square? I can’t find the answer - be it in Photoshop or on a paper. Pleas help!
If I understand well you are using a tablet for digital painting. I don’t know the principles of digital painting too well, so I’m not sure if using some tools other than a pen is allowed in this industry (I mean it’s not for noobs or something 
). Anyways… In my opinion, the thing is quite simple (if I understand your needs well). You can choose a tool for making squares or circles and while creating/drawing it if you press and hold the ʺshiftʺ key on your keyboard, you will get a totally perfect shape. After that you can run the modify mode (ctrl+t) and through RMB choose perspective which will allow you to play around with the perspective. Enter = confirm. After that you can draw whatever you want on it. Unfortunately, it won’t work on regular paper 
Well, one method is to draw a perspective grid.
There’s a good tool for that from Epic Games:
http://epicgames.com/community/2012/11/free-art-tool-released-thanks-to-epic-friday/
Video tutorial: http://ctrlpaint.com/videos/perspective-grid-utility/
A circle in perspective is an ellipse.
The confusing part is that the center of the circle in perspective is not the center of the ellipse.
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.