# Another quaternion question

How do I figure out the 'heading' vector given a certain quaternion representing the object's orientation.

Using directX I can get the rotation matrix. is there a way to do the invesre of the D3DXMatrixLookAt for the 3 vectors (or 1 of them for that matter)?

Cheers,
Krip
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Commented:
You can go back to a rotation matrix from a quaternion

D3DXMatrixRotationQuaternion

You can also try this

D3DXQuaternionToAxisAngle

Hope this helps
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Author Commented:
Maybe I wasn't clear...

I have the rotation matrix, what I'm looking for is the LookAt vector i.e. the vector in the same direction as my object's 'heading'

D3DXLookAtLH takes 3 vectors lookAt, eye and up and builds a rotation matrix from them. Is There a way to do the opposite?

Cheers,
Krip

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Commented:
If you know the original heading vector, all you need to do is rotate it by the orientation quaternion/matrix. That is, if the original orientation vector (say v) is (0, 0, -1), you just need to use the matrix (let's call it M) to rotate it as M * v. You'll then have a rotated orientation vector, i.e. the "looks at" vector.
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Author Commented:
Naturally....
Thanks
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