I would like to know if it's possible to rig imported obj. or fbx. characters
for animation? I've attempted this but with problems. Has anyone done this successfully?

Imported obj file contains geometry only, and rigging process should be pretty straightforward. So, could you elaborate a bit about problems you encountered?

Same thing is with fbx. If you export/import geometry data only, rigging process should be straightforward…

I've Imported FBX formatted rigs with animation as well….the process went well. The animation data arrived uncorrupted and useable. The rig ‘looked’ like a skeleton, but I was told that the FBX ‘import’ didn't construct the bone objects…they were merely ‘visualizations’ of the bones….ah…okay. They ‘render’ out as a chain…but not incoming…?? When I read ‘answers/explanations’ like these, I turn in a new direction…..

Then I tried to setup IK solutions with this same rig, and where things started to go wrong…with rotation order.

Then I discovered the ‘rig’ that imported wasn't constructed as if you'd construct a skeleton from the ‘ground up’, and would probably not work well with any IK solution. I'll be honest; I ceased pouring time into this aspect of the program.

I ‘believe’ the thrust of this Thread: how do you deal with Imported FBX rigs, for setting up IK..??

Cheers!

I'm finding that the skeletons don't form to the mesh or in the case of FBX they distort.

Not sure about your particular FBX file, but here's something that may clarify it. Houdini's rigging and IK is done on bones, whereas most FBX skeletons are represented using joints instead. The joint-based system is by definition more flexible than the bone-based one, and you cannot convert an arbitrary joint-based system into a bone-based one without losing or distorting data.

This is why the FBX importer, when it finds a skeleton in an FBX file, mimics the joint-based system by creating null nodes for every joint. It also creates bones between these nulls/joints, but these bones are for visualization only. All the vertex weights are stored in the nulls instead.

This means that, in particular, Houdini's IK algorithms won't work on this setup, since they only work on chains of bones. However, there's nothing preventing you from unbinding imported nulls (or not importing them to begin with), and re-rigging the mesh.

Alternatively, you could write a quick script to automatically create a proper bone-based system based on a particular static snapshot of the joint/null-based system, and go from there.

If a joint based system is more flexible by definition, why does Houdini uses bones?

while oleg may be right about joint based systems being ‘by definition more flexible’…having used both in production I strongly urge you to forget he even said anything about it…it doesn't matter…

as for the FBX stuff…
why rig in one app then import it into another app and expect a rig? if you're rigging in app A - stay there till the rigging/animation is done, then, if you need rigging type stuff in app B, FBX will give you nulls - more than enough to start with IMO.

haha, ok .. now I'm really curious. I've used 3ds Max and Houdini for rigging. They both seem to have the same idea going with the bones etc. What exactly are joint based systems; which applications use them?

Maya.

Alternatively, you could write a quick script to automatically create a proper bone-based system based on a particular static snapshot of the joint/null-based system, and go from there.

Well, I guess I was under the mistaken impression this is what the Import process was doing for me, so I could begin using it in HD?? This was a eye opener and something not expected, to begin working in a ‘new’ schema and find out what you've been given in the UI, isn't going to cooperate with the existing IK math.

…if I could just ‘whip’ up some sort of script to build a rig, I would, and I'd be set; guess I'm more the hammer and chisel artist than mathemagician….I can script for my game engine….I've assembled skeletons from text…I've assembled skeletons with geometry pointers…and mere Tree hierarchies…and I feel HD even has to potential to generate scripts, I'm not a level to assemble all these pieces with no guide…, willing to lead.

andrewlowell
What exactly are joint based systems; which applications use them?

As mentioned, Maya is joint-based. Also, Cinema4d and Lightwave are now joint-based, as of C4d r11 and LW 9.5.

Here is some more info: http://www.okino.com/conv/skinning.htm [okino.com]