I have two points in 3d space, cameraPosition and billboardPosition. In addition to this i have their normals. I want billboardPosition to be rotated so that its normal points at cameraPosition. basically...I'm stuck. I've found the equation of the vector that passes through both points using equation (18) on http://mathworld.wolfram.com/Line.html (its the correct one to use yeah?). So how do i go about finding the angle between billboardNormal and the line i found? also is this the easiest way to go about matters or is there a faster/easier method?