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13 - Known Issue & Special Notice: Character Symmetry for OBJ & FBX Export

Posted By Miranda (RL) Last Year
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13 - Known Issue & Special Notice: Character Symmetry for OBJ & FBX...

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Miranda (RL)
Miranda (RL)
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In version 3.3, we improved symmetrical accuracy for the export FBX files. Characters that are continuously exported and imported from and to CC will no longer become increasingly asymmetrical. This is due to slight lopsidedness of the HIK Control rig affecting the bone and mesh alignment. There are some test results and known issue for your reference.
  • How symmetrical is the CC3+ character in OBJ format?
  • How symmetrical is the CC3+ character in FBX format?
  • Why is ideal level of symmetry in OBJ not achievable with FBX?
  • Known issue: The character does not appear symmetrical in the CC view-port and deviates from the exported variant.
  • Known issue: The character does not stand flush on the ground plane when exported in OBJ and FBX.
Miranda (RL)
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Q: How symmetrical is the CC3+ character in OBJ format? 

A: Vertices on both sides of the character are symmetrical down to the fourth decimal placement.  Descriptions and test samples below:
  • CC3+ Neutral Export OBJ
    • Testing done with Maya > Symmetry Selection Tool using the smallest Tolerance setting at 0.0001.
    • Successful mirror selection at lower Tolerance levels equates to better symmetry.
    • Mirror selection is easily achievable with CC3+ base.
      • https://forum.reallusion.com/uploads/images/64897d43-0424-4f6c-8c40-4cf5.gif

  • CC3 Neutral Export OBJ
    • Using the same test methods above, the CC3 base symmetry test performs poorly.
    • https://forum.reallusion.com/uploads/images/2b558d7f-0069-41c7-aa1c-c07b.gif

  • According to the tests above, the CC3+ neutral base symmetry has been drastically improved with vertex positioning accurate down the fourth decimal placement.


Miranda (RL)
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Q: How symmetrical is the CC3+ character in FBX format? 

A: The figure is less symmetrical compared to the OBJ format. The symmetry test in Maya only passes when the Tolerance level is increased to 0.0005. Explanations and test samples below:
  • Test by using Maya > Symmetry Selection tool. Use Maya's default value of 0.0001 as the starting value.
  • Successful mirror selection at lower Tolerance levels equates to better symmetry.
  • When Tolerance is set to 0.0001, the mirror selection fails the fidelity test.
    • https://forum.reallusion.com/uploads/images/3454de9e-2c45-4146-a30b-e864.gif
  • Mirror selection passes when the Tolerance level is increased to 0.0005.
    • https://forum.reallusion.com/uploads/images/61a4a184-2571-417a-9b00-c313.gif
  • It is safe to conclude that CC3+ FBX is not as symmetrical compared to the OBJ format and only passes the symmetry test when Tolerance is set to 0.0005 or above.
Miranda (RL)
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Q: Why is ideal level of symmetry in OBJ not achievable with FBX? 

A: The FBX exporter performs a few special operations that causes inconsistencies in the data, explained below:

The CC morph data also contains bone scale data alongside the ubiquitous mesh offset data. Take the following baby model as an example:


Bone scale and mesh deformation data are two critical parts of puzzle when the neutral figures is morphed into a baby.
FBX exported from 3DXchange without additional processing into Max or Maya will retain bone scale inheritance data. 
This become apparent when the said figure is stripped of it's skin-weights inside Maya (Unbind Skin) as the figure changes in size and proportions.
https://forum.reallusion.com/uploads/images/449ac931-dbab-452b-bab7-c268.png

So we'll need to perform some addition steps in CC for FBX export:

1* Load the current mesh and keep its current shape (like the baby shape).
2* Reset bone scale to 1 and re-skin the mesh from step 1 and notice that there are some minute changes to the mesh data.

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Known issue: The character does not appear symmetrical in the CC view-port and deviates from the exported variant

Currently inside CC3 and iC7, the pose and animation systems are driven by the HumanIK control rig on top of the Motion Bones.
Because the two systems do not map to each other perfectly, the symmetry in the view-port breaks down on extreme close-ups (with the camera set to orthogonal).

Looking at the video below, it becomes apparent from careful observation, that the symmetrical points on the mesh do not line up perfectly in the side view.
  • Camera is set to orthogonal.
  • Select any point on the mesh and perform Edit Mesh > Mirror Selected and switch to the side view.
  • Zoom in up close and see how the two points do not line up perfectly.


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Last Year by Miranda (RL)
Miranda (RL)
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Known issue: The character does not stand flush on the ground plane when exported in OBJ and FBX 

When the following character are exported in OBJ and FBX into a 3D application like Maya - unless it is the CC3+ neutral base (left figure) - will likely penetrate into the floor plane.
https://forum.reallusion.com/uploads/images/5e4de56e-d249-4da8-874f-ec87.png

Reason: For the better matching, the HumanIK rig will be removed before the character is exported to OBJ and FBX. If the rig is not removed, then discrepancies will exist in the data which is similar to the view-port problem described in the previous post. The character is kept on the ground in CC because the HumanIK control rig is equipped with the floor contact mechanism. Once it is removed for export (OBJ, FBX) the character no longer adheres to the floor plane. However, this has no effect on the character when it is brought back into CC and creating morph sliders will still be based on the character standing flush on the floor plane:

https://forum.reallusion.com/uploads/images/57264433-8f7b-4df2-9eea-9ee1.gif
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Known issue: The character does not stand flush on the ground plane when exported in OBJ and FBX



I wonder if you guys are working on the fix. It really causing some unnecessary problems with exchange between various 3-rd party apps.







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