Coordinates of 3D model and tracts

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Kevin Jiang

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Feb 28, 2025, 2:21:25 PMFeb 28
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Hello,
I try to export the 3D model and tracts separately. So I saved the 3D model as .obj file and tracts as .mat file. Then I used the python package Pyvista to visualize both of them. The following is what shows in DSI Studio. (the region was reconstructed from template and all tracts are inside the region)
brain_stem.qsdr.image.jpg
This is what they are in Pyvista. It seems that they don't share the same coordinate system in the studio. How can I export them in single coordinate system.
Snipaste_2025-02-28_14-03-27.png
I have tried these options but they didn't work
Snipaste_2025-02-28_14-21-01.png

Frank Yeh

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Feb 28, 2025, 2:38:20 PMFeb 28
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You can save tracts to .obj 
https://www.youtube.com/watch?v=X9PvIRsGiZA

Kevin Jiang

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Feb 28, 2025, 3:40:38 PMFeb 28
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Hi Frank,
Thanks for your reply. I tried saving tracts to .obj but it doesn't contain the orientation information of tracts. I aim to assign the orientation of tracts to voxel elements for finite element simulation.

Frank Yeh

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Feb 28, 2025, 4:01:12 PMFeb 28
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You may save the tract as .txt format to extract the trajectories. obj
is mostly for rendering.
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Kevin Jiang

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Feb 28, 2025, 4:18:08 PMFeb 28
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Exactly, both .txt and .mat can be used to extract trajectories. And this is where I encountered the problem. Tracts seems to be defined in a coordinate system and the mesh of 3D model seems to be defined in another coordinate system. Maybe it's the reason why there is a translation between them. So I want to export them in one single system

Frank Yeh

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Feb 28, 2025, 5:40:47 PMFeb 28
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I will review the code and see if I can find a clue of the differences.
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Frank Yeh

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Aug 26, 2025, 2:05:08 PMAug 26
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Sorry for getting back to this late.
I don't see there is a translocation between them.
Both tract and meshes are in the same voxel coordinates.
Frank

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