I learned about fractional charges in particle physics.
Years later, I was working on Appel's Vector Hidden Line Removal algorithm at Mitsubishi, where you propagate the visibility by keeping track of the number of front facing surfaces obscure an edge. I ran into pathelogical cases when you project CAD bodies into 2D. Verticies land on edges, edges on verticies, verticies on verticies, and edges on edges. I thought of ideas in high school geometry where we would deal with half space problems. I used these concepts in my VHL algorithm. http://wheger.tripod.com/vhl