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

Rangi Sutton rsutton at dnahelix.com
Wed Mar 22 12:22:38 EST 2006

Peter Bowmar wrote:

>     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 ;)



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
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 ;)


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