And Maw! This

WTF XNA, Quaternion to Euler conversion

March 11th, 2008

Okay, so, XNA has quaterions, so you have {x,y,z,w}
Lets say you want to turn that back into {yaw,pitch,roll}
So you hit up Wikipedia and find some equations:

{x,y,z,w} = {q0,q1,q2,q3} right?
Well…NOOO, freaking XNA, that’s not right, hmm, perhaps its alphabetical?
{w,x,y,z} = {q0,q1,q2,q3}???

Once again, XNA slaps you around for nooo reason, here’s the right match-up:
{x,y,z,w} = {q2,q1,q3,q0}
{w,y,x,z} = {q0,q1,q2,q3}

Also, here’s some code to turn a quaterion into a vector of pitch,yaw,roll

public Vector3 QuaternionToEuler(Quaternion rotation)
{
float q0 = rotation.W;
float q1 = rotation.Y;
float q2 = rotation.X;
float q3 = rotation.Z;

Vector3 radAngles = new Vector3();
radAngles.X = (float)Math.Atan2(2 * (q0 * q1 + q2 * q3), 1 – 2 * (Math.Pow(q1, 2) + Math.Pow(q2, 2)));
radAngles.Y = (float)Math.Asin(2 * (q0 * q2 – q3 * q1));
radAngles.Z = (float)Math.Atan2(2 * (q0 * q3 + q1 * q2), 1 – 2 * (Math.Pow(q2, 2) + Math.Pow(q3, 2)));

Vector3 angles = new Vector3();
angles.X = MathHelper.ToDegrees(radAngles.X);
angles.Y = MathHelper.ToDegrees(radAngles.Y);
angles.Z = MathHelper.ToDegrees(radAngles.Z);
return angles;
}

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