This is basically it, yes, along with cos(x) = 1. If the axis of rotation is much further than the distance that you move through upon rotation, the angle of ro

This is basically it, yes, along with cos(x) = 1. If the axis of rotation is much further than the distance that you move through upon rotation, the angle of rotation is very close to zero, so the approximations are very good. In the limit that the axis of rotation is infinitely far away, it is exact.