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Poser Python Scripting F.A.Q (Last Updated: 2024 Dec 02 3:16 pm)

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Subject: WorldQuaternion - broken?

face_off opened this issue on Jul 11, 2005 · 5 posts
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face_off ( ) posted Mon, 11 July 2005 at 10:01 PM · edited Wed, 30 October 2024 at 1:00 PM

OK, I've been working on a major Poser application, and been stuck on a roation problem from about a week now. To cut a long story short, I'm trying to get a rotation matrix from a quaterion from Actor.WorldQuaternion. Now I've tried a number of methods for converting the quaternion to a rotation matrix - including http://www.flipcode.com/documents/matrfaq.html#Q54. The rotation for the X and Z axes is comes out ok, but not the Y Axis. So I did some tests.... A prop with 10 degrees X Rotation gives a Quat of (1.575, 0.1378, 0.0, 0) - where the tuple is ordered W, X, Y, Z. 10 degrees Z rotation gives (1.575, 0.0, 0.0, 0.1378) - notice the same magnitude, and X now at Z. But 10 degrees of Y rotation gives (1.571, 0.0, 0.2210, 0.0) Notice the magnitude has changed, and the Y variable is not the same as X/Y in the previous examples. Converting the 10 degrees Y rot quat into a rotation matrix and then working out the euler angles introduces a 2-3 degree error in the Y rotation. But it only happens on the Y rotation - X and Z are ok. Anyone got any thoughts on this?

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PoseWorks ( ) posted Tue, 12 July 2005 at 12:53 PM

Is it related to the change in W?

stewer ( ) posted Tue, 12 July 2005 at 2:29 PM

file_269788.jpg

WorldQuaternion() seems to have problems with objects that are not scaled at 100%. I ran into the same problem once and wrote my custom routine to extract a quaternion from WorldMatrix().

face_off ( ) posted Tue, 12 July 2005 at 5:31 PM

Stewer - thanks for your code sample. And YES - I noticed it's only a problem when the object is scaled! I ended up simply extracting the rotation matrix from the world matrix. Although I noticed you've got a different way removing the scale from the WorldMatrix - which I need to lok at. Anyway, thanks again.

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an0malaus ( ) posted Sat, 16 July 2005 at 9:35 PM

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