Art and drawing has always been a mental process even when I used charcoal. It’s not the hand but the brain at work.I first thought of the idea represented by the above image in 1966. My initial thoughts were about flying through and around a drawing in 3d. But I had to wait a long time before raster graphics appeared. The idea needed lighting models to give emphasis to 3d cues. Fog or atmosphere helps. An animation language had to be invented along with procedures using bicubic patches and b-splines for the lines.
The movement and direction of the lines in my image are determined by the vertex points of invisible objects. The bspline provides nice curvature. Later, you might enjoy my flight throughout the drawing.