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Date: Sat, 1 Jul 1995 17:47:27 -0400
Subject: Re: Bone hierarchy in LW
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On Thu, 29 Jun 1995 [e-mail] wrote:

> Is it just me, or do other LW users have difficulty positioning children
> bones whose parents' heading and pitch have been adjusted?

This is a normal "problem" with any object that's been parented to
something else...when manipulating a child object(or bone), you're no
longer changing the child relative to the LW "world" but relative to the
parent object.  So, if the parent object is altered, then the child
objects will be altered also and will move in relation to the parent's
new position/rotation.


> The reason I am asking is so I can position bones in a character whose arms
> and legs are separate objects.

Try modeling your seperate limb objects aligned with the Z axis and with
their main pivot point at 0,0,0.  In other words, after you model you arm
object, rotate and move it so that the shoulder rotational point is
positioned at 0,0,0 and the hand points straight down the +Z axis.  Save
or export this object to Layout and start adding bones...you'll find that
the bones are automatically aligned with the object already and all you
have to do is tweak their rest length.  Don't move this object until you
have the skeletal structure all laid out and have the Rest positions
set...then parent the arm to your torso object, and rotate and move it
into position, relative to the torso.

What all of this will do is leave your bones' rest rotational values
untouched, so that when it comes time to bend the arm into position, all
of the Heading and Pitch rotations will come easily and you won't have to
worry about the "gimbal lock" thingy, or whatever it's called.  =)


>   I  also am trying to have seamless joints
> between the torso and arms.  Are a number of limited region bones the way to
> tie down the seam while allowing for movement of the rest of the arm?

Limited Region bones are usually only good for subtle movements, like
facial expressions, but they may work in this situation.  You may have
more success by just adding a standalone bone (not parented to anything)
with unlimited region and position it at the inner edge of your arm
object's shoulder joint.

There are many other tips I could give you on making this work, but I'm
beginning to experience "gimbal lock" in my wrists!  =)  Besides, I think
I have another topic for an upcoming tutorial in LightSpeed!  (whaddaya
think, Manny?)  :-)


Hope this helps!

                                      -David Warner
                                       Event Horizon Graphics


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