-->question part<-- The part that I''m wondering about is how do you find the intersection of a vector and the triangle''s plane, given the triangle''s three points (or possibly the normal if you need that). Notice I said vector, and not ray. That should be an easy question, but it stumps me. I have the following worked out though: Thanks for any help. darrennix@msn.com -->solution part<-- A point is in a triangle if the point is contained by all three of the triangle''s angles. A point is contained if its angle from an edge is less than the angle. In other words, if(ptinangle(point, a, b, c) && ptinangle(point, b, c, a) && ptinangle(point, c, a, b)) // it''s in the triangle! bool ptinangle(CONST POINT &v, CONST POINT &v0, CONST POINT &v1, CONST POINT &v2) { double fTheta = acos(((v.x-v0.x)*(v2.x-v0.x)+(v.y-v0.y)*(v2.y-v0.y))/(mag(v-v0)*mag(v2-v0))), fAngle = acos(((v1.x-v0.x)*(v2.x-v0.x)+(v1.y-v0.y)*(v2.y-v0.y))/(mag(v1-v0)*mag(v2-v0))); if(fTheta < fAngle) return true; return false; } That''s in 2D because I wrote a simple test app that fills all points with a color depending on whether they''re in the triangle. Email me if you want to see it.