Start of a module for coordinate frames.
Working on arrowheads, I realized that I was doing all rotations within world coordinates. Clearly this was wrong and the obvious solution is to add frames (with origin and ortho vectors). I've done this but I'm stuck on how to integrate them. With homogeneous coordinates there is an immediate relation between t1 t2 and the frame within the transformation matrix:
1 0 t1
1 -1 t2
0 0 1
But I'm not sure what the relation actually is and I don't know what operations a frame should support. The presentations I've seen quickly move from frames to homogeneous coordinates and I'm failing to deduce the connection.
