[X3D-Ecosystem] Rotate bone around what? Found pivot in Blender API

[Joe D Williams]

> Head is 0 

Same as parent Joint of Segment representing that bone. 
The geometry for that bone must be positioned so that
it operates as expected. 
So, it is possible that this 'constraint' allows adjusting the
geometry pivot point so as  to work right. 

In any case I think this does not change the
bone head as parent Joint center location
but probably is more like a hack to move
geometry because the geometric end of the bone
is not typically the correct geometric pivot point. 

x3d and HAnim would take care of this by correctly
transforming the geometry to the correct location
in the first place and not use this parameter.

So, if this term is not 0 then the affected
geometry would need to be translated to
compensate for hanim lack of this parameter? 
Hint: it is lacking because it is not needed.

If this 'constraint' could be animated it might work
like a piston:)  

All Best,
Joe

   
-----Original Message-----
From: John Carlson <yottzumm at gmail.com>
Sent: Jan 16, 2025 9:47 PM
To: X3D Ecosystem public discussion <x3d-ecosystem at web3d.org>, Joe D Williams <joedwil at earthlink.net>, Katy Schildmeyer KS APPAREL DESIGN <katy at ksappareldesign.com>, Carol McDonald <cemd2 at comcast.net>, <hanim at web3d.org>
Subject: Rotate bone around what? Found pivot in Blender API

class bpy.types.PivotConstraint(Constraint)Rotate around a different point
head_tailTarget along length of bone: Head is 0, Tail is 1
TYPE:float in [0, 1], default 0.0


So in Blender, one can rotate the bone along any point in its length, from 0 to 1.
AFAIK, I am setting the joint center to the bone head.  I don’t understand what I’m doing wrong, but the next step is to look at how skin weights/vertex groups work in Blender.  AFAIK, the skin is okay, and the rig is okay.  So now we need to narrow down the search to how vertex groups are set up in Blender as opposed to skin coord info is set up in X3D.  I think we can set bone center to rest, except perhaps discussion about humanoid root.  Bone head is joint center, unless you like weird, non-default setups.  Should these be handled?
I believe there are other options for non-bone objects.  Thanks to Joe for helping me sort through miscreant iOS web search.
If anyone is setting head_tail to something other than 0 in Blender, grr.
John 

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