maybe the term projection is not correct, my apologies
I will give you an example:
you draw a circle
then you copy that circle and paste it a bit further
then if you connect with the proper lines these two circles, you will have a cylinder!
this is what I am trying to do, but for more complicated 2D drawings
simple copy/paste works to draw the second circle, but the tricky part is to draw the lines to connect the two 2D drawings, as they maybe needed more than two simple lines to give that 3D effect