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in reply to Re: Rotate a 3D vector
in thread Rotate a 3D vector

how do you find the angles , , and between two vectors?

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Re^3: Rotate a 3D vector
by Anonymous Monk on Apr 28, 2010 at 23:02 UTC
    To find the angle between the two vectors, you need to normalize them (so they have length of 1 unit) by doing this (v is the vector you want to normalize):
    float distance = sqrt(v.x*v.x + v.y*v.y + v.z*v.z); v.x = v.x/distance; v.y = v.y/distance; v.z = v.z/distance;
    Then find the dot product of the two normalized vectors (Va and Vb):
    float dotProduct = Va.x*Vb.x + Va.y*Vb.y + Va.z*Vb.z;
    This gives you the cosine of the angle, so simple do:
    acos(dotProduct);
    This will give you the angle. I think this post was a bit late :S