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Joints position extraction
October 26, 2017
7:11 am

Hi, I'm dealing with the output .dae file and want to extract the joints position from the file to plot the skeleton in my project. After I found the "visual_scene", I visit all nodes and get their information of translation and rotation like showing below. So I translate x, y, z based on their parent's position and rotate it by Y, X, Z axis by their degrees respectively. But the skeleton I plot goes to a mess. Is there anything I missed during this process? BTW, the 'inverse_bind_matrix' is the identity matrix. Hope you could help me with it.


<translate sid="translate">-0.088257 -0.092568 -0.056613</translate>
<rotate sid="rotateY">0 1 0 -97.791161</rotate>
<rotate sid="rotateX">1 0 0 -1.866507</rotate>
<rotate sid="rotateZ">0 0 1 87.608734</rotate>
<rotate sid="jointOrientY">0 1 0 0.000000</rotate>
<rotate sid="jointOrientX">1 0 0 -0.000000</rotate>
<rotate sid="jointOrientZ">0 0 1 0.000000</rotate>


October 30, 2017
2:10 pm
Forum Posts: 985
Member Since:
December 1, 2011
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You have to reconstruct the skeleton hierarchy based on the translate, rotation and orientation that you see. I would suggest looking at the COLLADA documentation for details.


October 31, 2017
6:52 am

Hi Ari,

I finally extracted the skeleton by:

1. Translation

2. Rotation

3. Multiply the Inverse_Bind_Matrix (IBM), which is neglected by me before.

But there is still one joint named "JtJawFront" apparently wrong among them. I don't know why.

The number of joints needs to be transformed by IBM is 77 but the visual_scene defined 89 joints. So they are 12 useless joints in this tree, "JtJawFront" is one of the them, but it is the parent of three useful joints, so the bones between them are wired. And it still cannot match the .ply model when I plot them together in R, seems like the whole body skeleton needs to be moved up or down a little. 

The last question is that the AutoRiggerandReshapper always quits when process the big .ply file, for example, 210000 vertex and 420000 faces. Is it some size limits of the it? It's quite a problem for me cause I need to process large 3D models.

Kind regards,

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