I'm following this example on finding the intersection point between a plane and a line. (it's about three quarters down)
http://paulbourke.net/geometry/pointlineplane/
However this seems to only show how to solve u.
1. I don't understand what u is.
2. How do I find out the intersection point, in terms of (x, y, z)?
Edit: as you are using normal vector and delta to define the plane, I think that the formula is u = (pln.d-dot(pln.n, p2)) / dot(pln.n, p1-p2); (maybe confused p1 with p2)