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betty

Handle OBJECT/CHOP

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ok, i'm back at trying to make sense of these character tools which i'm struggling with.

the latest thing to get me is the handleOP at the object level. now i'm reading that this works in tandem with the handleCHOP. i've played around with these but cannot seem to get anything going.

has anybody used these with any succees?

betty

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They're mainly intended for mocap data where each bone can "reach" for several marker null objects.

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They're mainly intended for mocap data where each bone can "reach" for several marker null objects.

Hi Edward,

The Handles have always intrigued me...

Do you have an example of their intended use? I'd love to see how these were designed to be used. Also, how best to to these for custom rigs that don't use motion capture data.

Cheers!

J.

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Hi Jason,

I don't have one offhand right now at home but the way it works is like this. To each bone, you append one (or more) Handle objects. Each handle object can be positioned along the length of the bone and then extended outwards. For each of these Handle objects, you specify a target object which it will "reach" for, pulling its parent bone along with it. And then you create a Handle CHOP giving it all the bones to control and it will solve the bone rotations which you then export with. I can dig up some notes I have on using the Handle CHOP and probably a contrived hip file too if anyone wants.

The idea again, is that this was intended for mocap data. You first have a program which creates a null object for each mocap marker. So now you have all the markers animated in Houdini as Null objects. Now you go to frame 1 and for each bone in your skeleton, select some mocap markers for it in the viewport. Once you have the bone and its markers selected in the viewport, you press a function key which runs a script that creates all the necessary Handle objects positioned at exactly where each marker is extending from the chosen bone. If anyone wants, I have a script which does this. Once you have all the markers associated with the bones, you then create a Handle CHOP to solve everything. You can also specify bones that are supposed to move in synch with each other like shoulders and pelvic bones. At the end of all this, you can then use the raw edit tools in CHOPs to do further clean up. This is where CHOPs is really good for cleaning up of mocap data.

The primary advantage of this system is that you can effectively have more than one "end affector" for each bone. However, it's a purely iterative solver in which you need to specify how many iterations to solve and the maximum angle to move a bone at each iteration. So it needs more tweaking in order to get the solution you want.

On the otherhand, if you want inexact solutions, this would be your best bet (soft-IK maybe?). It gives you control over the "looseness" of the bone solutions. I'm not really sure how you would use this in custom rigs. Maybe floppy ears by animating the number of iterations in each frame over time? Maybe you can come up with some situations where it is easier to control via multiple end affectors per bone. Ideas? :)

-Edward

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Er, after saying all that, just wanted to note that Houdini also has command line utilities which convert some common mocap formats into script files which can be sourced into Houdini. They are: mcacclaim (Acclaim), mcbiovision (Biovision), mcmotanal (Motion Analysis). For further info on this, see the Using Motion Capture Data in the CHOPs chapter of the manuals.

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Thanks for the info, Edward..

It's odd, I've seen these executables and ops in Houdini for quite some time but I haven't yet seen any mocap work in Houdini yet. Do you know of any pieces done using the mocap tools in Houdini recently? I feel there's an untapped strength in Houdini for motion capture work. Do could probably do some simple retargeting of animation within CHOPs as it is quite easily.

Actually Edward, I'd find it very enlightening to see a hipfile demonstrating the Handle ops if you can whip one up. One thing I noticed is that the CHOP doesn't recook automatically if you adjust the handle offsets interactively. (I guess it's an OP_Interest thing?).

Thanks!

Jason

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Hi Jason,

Ok, I'll try to come up with a sample file sometime then but it might have to wait until the weekend or the week after. Goodie, I can now do something with the japanese CD of Prisms/Houdini mocap data which we found while cleaning up. :)

As for who has been doing mocap work recently, Jeff or Peter would know a lot better. The last person I talked with about using the Handle CHOP was with Simon Barrick. If you find out anything, let me know. :)

-Edward

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