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freespark

Bone capturing

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Hello all,

I know this is probably a real pain, but what are some general rules of thumb for capturing geometry particularly in the shoulder region so that the geometry doesn't buckle or bend in a weird way. I am particularly having this problem with the shoulder region. I must say though, setting up bones and ik constraints in Houdini have never been this easy. I really enjoy it. Any suggestions, tips, and habits are much appreciated.

Nevins Duret

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Sorry, had to move this to the character section since its pretty much a weighting/boning problem.

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Well, I am no character animator but I understand that this is tricky area, which involves all the issues - modelling, weighting & deformation. There are some great tips for modeling shoulders out there on the web - try Bay Raitt, (an excellent modeler who worked on Lord Of The Rings) for some tips.

There are various papers out there to try and solved the deformation problem - trying to steer away from linear deformations and toward only solutions, like the Siggraph paper on "Pose Space Deformation" and such. I dont know anything about the simple tricks except I discovered how easy it is to take a character, deform him into a position where the problems are bad, Sculpt SOP the danger area, re-wire the Sculpt SOP to before the Deform SOP and then blend the new position in based on a simple boneangle() expression. This will yield non-linear deformations which work quite well.

I love that you can re-wire the Sculpt SOP like that, to effect the same changes to the rest position as you did to the deformed model. I'm pretty certain some more research into this will give some good results. Perhaps you could look at that?

Cheers!

Jason.

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Hello Jason,

Thanks much on that quick reply. It's a really good resource. My problem is not the modelling, it's definitely in the weighting and deformation prodedures. This is what I'm struggling with. But thank you for bringing the new sculpt tool to my attention, I knew it worked procedurally along the same lines as the edit sop, but i had no idea you could remove it from the network and place it before the deform SOP. The only thing I don't quite get is the "then blend the new position in based on a simple boneangle() expression", -where specifically do I get info on this? When you mentioned blend, I thought the blend sop with the existing scult node would work nicely sense the blend sop affects points weight. This is the part I don't quite get. Again, I thank you for the response. I will definitely give this a try.

Nevins

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Hi Nevins,

Recently I learned the Blend/Sequence Blend deformation technique. This technique was probably been used in the industry for quite some time now. It was shown to me by one of my good Mayan friend here using Set Driven Key BlendShape.

Houdini's approach is very similar, however, the only thing is that you will have to use the expression to control your "set driven key". So for area that is very complex to control (i.e. shoulder), this approach works extremely well. However, for other area, such as your stomach, you can simply use CapturePaint SOP to paint weight on the character.

I like the "set driven key blendshape" (sorry, not quite certain what to call in Houdini) approach because it gives me full control over my model's topology. This way, I can keep my them clean because I am basically modeling the deformation in.

As for the expression part, it can get kinda nasty. Therefore, I would keep things a little bit cleaner and possibly simpler by writing my own custom expression function to control the blend. Say, if you have to rotate your arm at X axis only, you'd use expression to control the Blend/Sequence Bblend weight if bone_x approaches certain angle. The if() and fit() will be used a lot I would say.

It's quite simple really. I really like it. And like Jason said, I can always go back to tweak it. :) However, in Houdini, this technique is not a "magic button" approach either and at times, it will call to your problem solving skills.

But this technique ought to make it slightly easier for a very complex area like the shoulder. :)

Cheers!

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Hello Alex,

Again, another quick reply. I can't thank you guys enough for getting back to me on this. I will definitely try to icorporate these things in the way I set them up. The sculpt tool so far is very promising. Thanks again.

Nevins

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