Pete will put on reserve. We won't have good models for this course. Probably just triangles or something. Use whatever format you want. Triangle is just three points.
Rays are displacements.
Displacements add, points don't. But points average. They're different protocols so they shouldn't be the same thing. Type checking is a good but perhaps painful thing. Probably no reason to every have homo coords in a RT program unless you're gonna have a non-RT previewer.