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Johnny_Scott
04-19-2003, 03:39 PM
I'm having a problem and I hope sombody can help me resolve it.

The problem is that sometimes when I go to animate the rotation of bone objects in a fk hierarchy they shear as they are rotated.

I suspect that some sort of transformation is happening to the pivot point but I know that I'm not actually selecting the pivot point and giving it key frames. (see images below)

However, I usually have adjusted the pivot point of these objects from original and also done some non-uniform scaling to make them match the mesh of a character (there might be some no-no to non-uniform scaling of bones I'm not aware of, one ought to be able to adjust center of rotation). The objects I'm using for bones in this examble are dummy objects (it happens with meshes as well occasionally).

http://home.att.net/~johnny.w.scott/shearingexample.jpg
Image of shear, the red objects are linked top to bottom and are the ones shearing, the green object is for comparision it is rotated at the same angle as the lowest child in the fk hierarchy

MAX file... (http://home.att.net/~johnny.w.scott/shearingexample.max)

http://home.att.net/~johnny.w.scott/fishWIP.jpg
WIP character (study of pixar's finding nemo hero) destined to inherit bones that work(don't complain - I know that clown fish have fins...)
Johnny_Scott
04-19-2003, 08:49 PM
is anybody going to reply?

Could sombody who's read this far please reply with a simple "Sorry, but I have nooo clue!" if only to give me the piece of mind that people are in fact reading this thread but simply not having any answers for me..... thanks ;)
EricChadwick
04-21-2003, 06:56 PM
Parents have non-uniform scale. Re-create the dummies without using non-uniform scale, or remove the hierarchy and reset the scale for each dummy then re-link.

Or use Bones instead (but don't non-u scale, instead use the Bone Tools to change proportions).
Johnny_Scott
04-21-2003, 10:41 PM
Thanks for the reply posm :thumbsup: , I pledge never again to non-uniform scale bones again. :shame: oops, that's redundant!
EricChadwick
04-21-2003, 10:45 PM
It's weird, because Biped lets you non-u scale its bones. But all other linkage systems have ugliness with non-u scale.
Johnny_Scott
04-21-2003, 11:17 PM
interesting....I have never animated with biped, I've played with it but it felt confusing with the whole footsteps thing and a bit artificial with prepackaged walk-cycles (I understand they are really just for a foundation upon which to work from...)

I wonder what the non-uniform scaling restriction is about ...?:hmm:
EricChadwick
04-22-2003, 02:04 PM
The non-uniform scaling problem has to do with the order that transformations (position, rotation, scale) are applied to a child of another object.

A child object is given the transform of its parent first, then its own transform. When the parent has non-u scale, the child has to rotate through the parent's distorted space, thus the skewing. Uniform scale doesn't distort the parent's space.

However, in most cases you can non-u scale if you are in Sub-Object mode, since you aren't affecting the transform of the object, instead you're affecting the shape of the individual vertices.

I hope this helps.
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