Hi there all,

I'm practising with character tools like setting up bone hieararchies and IK systems using the apprentice version. Studying with training videos and buzz3d tutorials I had been able to achieve some nice results and going well so far.

I've setup a basic leg IK, made some automation with expressions and chops. Mirrored the half to make it symmetrical. Then I decided to load up a character geometry and reposition the bones to fit it. At first it might seem not the correct way to set up a character, creating the bones first then bringing the gometry, but when you think to use your custom rig to fit your other characters as well, it is necessary. And here the problems start…

I couldn't be able to reposition my bones symmetrically. I pick up the bones OP and start to scale and position the bones but the mirrored half stays fixed. And while repositioning them some strange things happens to childs in hierarchy, they change their positions and scales. Try to correct them and this time the parents starts to jump off.

I think there must be a way to reposition or edit your mirrored bones and hierarchy to fit into another character. I must doing something wrong there. Hope I could explain the problem clearly, and appreciate some help on the situation.

Thanx in advance,
Cya.

In Houdini, bones are pretty much any regular object except with some extra parameters. That means if you scale them, you will affect everything down your hierarchy. What you often want is to actually change the “Length” parameter instead of “Scale”. It's on the second page of the Bone object parameters. It's really much neater if you repositioned them using the Bones tool which will do the right thing.

As for mirroring object heirarchies, it's currently non-procedural as it simply makes a copy of your source hierarchy and more or less adds in a negative scale in the right places. So this means that moving the right side will NOT affect the left side. This is what people often want … for example, you don't really want moving the left leg to also move the right leg when animating.

Off the top of my head, some ways that one could approach this:
- Only create half the rig. When reusing a rig, bring it in, reposition the bones, and then mirror. This assumes that your rig is simple enough to use the object-level mirror tool though. Some extra script might need to be written to properly connect the mirrored side.
- Create a full rig. Only position one side. Now run a script which copies the bone positions from one side to the other. I had written a small script example on odforce before on how to position bones (here [odforce.net]) which may help.
- Do something even more automated (aka “autorigs”). Instead of bring in a bone hierarchy, bring in an hierarchy of null objects of where the joints should be. You can make this rig procedural in the sense that the right side will always follow the left side symmetrically. When you're doing positing the nulls, run a script which creates the whole rig from these nulls. This is a lot of work but at least it can be nicely encapsulated in a custom object subnet operator and distribute it as a .OTL file. You plop it down, position the nulls inside, and hit a button on it which creates the rig.

Thanks for the reply edward. While I'm using chops those are fed by the data from the left and right leg (like for positioning the root null automatically between the foot nulls), as you delete, or post create the other half then your preperations or premade chops goes to trash.

I thought of activating a symmetry button say in a mirror state while editing, then disabling it when it comes to animate. I see it is not easy or painless as I think of… sob

Thanks again for your kind reply.

Diya.