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# IK, constraining joints with quaternions

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Hi, I have already got some IK working using the very simple method that Jeff Landers described a while back. If no one rememebers I will give a short explanation in psuedo code. EEVector = IK Target - End Effector Angle = EEVector DOT BoneVector (parallel to the length of the bone) Normal = EEVector cross BoneVector Rotate bone Angle degrees around Normal. Simple right. Well I am trying out some constraint systems on it and its turning out to be a little expensive and prone to Euler problems. Can anyone refer me to some sources that can constrain Quaternions? It would be easy to convert the above to quats but after that I dont know how to constrain them without converting back to matrices and then I am back where I started. If you couldnt tell I am not proficient at Quats, I only know the basics on how to use them for rotations. Plus I apologize if this is not the right place for this question. If anyone can tell me where to post this question that would help too. Thanks, Kevin

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I ran into the same problem with my animation system about 8-10 months ago...I never had a decent fix for it, so I sort of left it that way..so far it hasn''t been an issue(we don''t actually use the IK system for anything, YET), but I know it''s sitting there in the code waiting to come back to haunt me. I would love to know the solution if someone has one. I went nuts with it for awhile, but couldn''t justify any more time spent due to other active issues(which affected features actually in use).

I''m keeping an eye on this one..Kevin_C, I''ll also send you an email if I find the answer. NOTE: If "finding the answer" involves long head-scratching hours _on_company_time_ without outside assistance, I won''t be able to share the results, but if I find it independently I will definitely let you know

"Like all good things, it starts with a monkey.."

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I found a couple things online which sounded promising but unfortunately I havent had time to read thru them yet. I have the same problem as you where I have to work on other things. In fact this IK stuff is what I have been working on when I dont have other scheduled stuff to do. Here are some links.

http://mech.polimi.it/azionamenti/pubblicazioni/archive/tasora_euromech404.pdf

http://ligwww.epfl.ch/~fua/papers/herda-et-al-fg02.pdf

I hope these actually contain information on the problem and I am not just posting crap.

I will probably get to take a look at these the beginning of next week.

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quote:
Original post by Kevin_C

Thanks, I''ll check them out over the weekend at home, then we can both benefit

"Like all good things, it starts with a monkey.."

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