Hi guys, I was wondering if someone could help me out with the theory and maybe even some basic code to the following problem.

I start off with a vertex and a quarternion to rotate. I calculate a second vertex from the quartonion which is fine. Now I have two vectors, I would like to calculate the angle between the first vector and my new second vector.

I decided to calculate the length of the line between the two vertexes with the following code

LineLengthX = sqrt((Y * Y) + (Z * Z))
LineLengthY = sqrt((X * X) + (Z * Z))
LineLengthZ = sqrt((X * Y) + (Y * Z))

This calculates the length of the 3 lines following the 3 angles.

I then thought I could calculate the angle by using trigonometry using atan, I now know the coordinates of a 3rd vector pointing 0 degrees as its Y is the length of the line calculated above with x being zero.

Put simply, Is that right?

Ultimately I am trying to work out the difference between two angles and then splitting it down into parts. For example if I wanted to create 3 vectors sitting in between my 2 vectors I could split the difference between the two angles by 3 and rotate the point by the angles.

I hope that makes some form of sense, I find it hard to explain, I think I am tying myself in knots hence i want to check I am heading in the right direction