While visiting the National Gallery of Art I learned about an interesting little machine called the Camera Obscura:
"Light from an external scene passes through the hole and strikes a surface inside where it is reproduced, upside down, but with color and perspective preserved. The image can be projected onto paper, and can then be traced to produce a highly accurate representation."
Many variations of the camera obscura have been used for centuries.
These artists were getting their basic outline by TRACING.
And it wasn't cheating.
I love this revelation as I have traced photos (cameras are just a modern Camera Obsecura with a way of keeping the image) to get basic shapes and perspectives on drawings and I thought I was cheating. Turns out I was just following in the footsteps of Canaletto and Leonardo Da Vinci!