[Sidefx-houdini-list] Converting FK to IK?

Peter Bowmar pbowmar at gmail.com
Wed Mar 22 12:48:02 EST 2006

Hey Rangi,
      Diddums indeed! Amazing what one simple script can do :) Fixed
all my problems in one fell swoop. No need to graft FK to IK etc etc.
Thanks very much!!
      I guess this has been broken for a while now? It was about
exactly a year ago you posted that... Anyways, you have saved my ass
     Say hi to the nice DNA folks from me :)


Peter B

On 22/03/06, Rangi Sutton <rsutton at dnahelix.com> wrote:
> Peter Bowmar wrote:
> >Hello,
> >     I'm kind of sick right now and my normally slow brain is moving
> >backwards it seems... I have some mocap data in IK (from Biovision)
> >that works OK (mildly broken but I can fix it with a script). However,
> >mcbiovision isn't bringing in the feet and hand "leaf" nodes so I
> >don't have hands :(
> >
> >
> Ah diddums ;)
> http://www.sidefx.com/index.php?option=com_wrapper&Itemid=151
> ------------------
> This perl script will add a redundant bone to the end of each skeleton
> branch since the houdini conversion script mcbiovision drops the last
> bone in any branch. You get your fingers, toes and heads back!
> $ bvhpad.pl orignal.bvh > padded.bvh
> $ mcbiovision padded.bvh
> My perl is so rusty the engine has fallen out, so caveat emptor. Most
> especially if your motion data lines have a leading space it screws up
> horribly. Someone fix that.. please?
> -------------------
> >     However, mcacclaim is correctly bringing in the feet and leaf
> >nodes, but has a lot of bone flipping problems so I can't use it
> >directly.
> >
> You can fix a lot of stuff simply piping these channels through a
> transform chop. Make sure you get the rotation order correct though..
> >Also, bizarrely, the scale is off. What I've done that seems
> >to work is take the FK Acclaim feet and hand objects and graft them
> >onto the IK from Biovision to create a complete character. All fairly
> >easily scripted so far.
> >     What I can't get my little brain around is converting the FK
> >hands and feet (mostly the hands) to IK so I'm not mixing editing
> >solutions when it comes time to edit this frankenstein monster. IK has
> >a lot of advantages over FK for mocap editing, I've found recently :)
> >    So, anyone have any ideas? I was thinking I could put a null as
> >the child of the FK bone, then use a Geometry CHOP to capture its
> >world position space, then I'd have an affector and then convert the
> >bone to IK. Does that make sense though? I could script that pretty
> >easily too I'd think...
> >
> >
> You pretty much have it but I think your making life hard on yourself.
> Parent a null to your FK creatures bone and that's your IK end affector.
> You probably want to parent another null to the previous bone to create
> a twist affector, or maybe keyframe this otherwise you might find
> yourself recreating the flipping ;)
> Beers,
> r.
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