Points within regions


to determine if a point is within a region 


	1. draw a line through the point in any direction


	2. if the line crosses the boundry at two points, a and b,

		and the distance a->c + c->b = a->b then the

		point is within the region. If no such situation
	
		exists, the point is not within the region. 


		The existance or otherwise of other points at which the line

		crosses the boundry does not affect this result.


		applicable to 2-d, 3-d etc. shapes, regions


no proof derived




Hidden surface removal


	Draw a line from a point on the surface to the viewer.

	if the line crosses a surface, and the distance x->v is

	less than the distance p->v, then the surface with the 

	point 'p' on it is hidden by another surface, and shouldn't

	be drawn. (the surface with the point 'x' on it would be).




(no proofs avail.)
