# Keep lung from different subjects has the same number of nodes/ landmarks

**URL:** <https://discourse.slicer.org/t/keep-lung-from-different-subjects-has-the-same-number-of-nodes-landmarks/32814>\
**Category:** Support\
**Tags:** segmentation, pca\
**Created:** [November 14, 2023, 5:29pm UTC](https://discourse.slicer.org/t/keep-lung-from-different-subjects-has-the-same-number-of-nodes-landmarks/32814 "2023-11-14T17:29:18Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Chuan](https://avatars.discourse-cdn.com/v4/letter/c/4da419/32.png) [@Chuan](https://discourse.slicer.org/u/Chuan)\
**Post date:** [November 14, 2023, 5:29pm UTC](https://discourse.slicer.org/t/keep-lung-from-different-subjects-has-the-same-number-of-nodes-landmarks/32814/1 "2023-11-14T17:29:18Z")

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Hi,

I need to do the segmentation for lung in different subjects. And then I need to conduct principal component analysis (PCA).  
Because usually PCA needs the landmarks information, and every subject must have the same number of correponding landmarks.  
I am wondering if it is possible that in 3D slicer, when I export my segmentation file as stl file, it can make every subject’s stl has same number of nodes. So that I can directly use node information in STL file instead of marking the landmark manually.

Or is there any plug-in that I can use to change the node information of stl/ segmentation model to make it corresponding to my reference STL model. Because what I want is just to make every lung geometrical model has the exactly same number of nodes.

Best regards,  
Chuan