# Aligned SPHARM models flip inside out during PCA

**URL:** <https://discourse.slicer.org/t/aligned-spharm-models-flip-inside-out-during-pca/30768>\
**Category:** SlicerSALT\
**Tags:** spharm-pdm, 3d-model\
**Created:** [July 25, 2023, 12:58am UTC](https://discourse.slicer.org/t/aligned-spharm-models-flip-inside-out-during-pca/30768 "2023-07-25T00:58:16Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![ayersmanmal](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/ayersmanmal/32/67119_2.png) [@ayersmanmal](https://discourse.slicer.org/u/ayersmanmal)\
**Post date:** [July 25, 2023, 12:58am UTC](https://discourse.slicer.org/t/aligned-spharm-models-flip-inside-out-during-pca/30768/1 "2023-07-25T00:58:16Z")

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Operating system: Windows  
Slicer version: 4.0.1  
After following through with the shape population analysis module, the resultant PCA output has the models turning inside out. Since the three SPHARM.vtk files that make up the PCA have no obvious issues why does this happen?? For reference, the included screenshots show the inside out problem; attached as well are the models that had been aligned prior to shape pop. analysis and uploaded to slicerSALT

 ![Mean shape](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/2/b/2b1284cbd5e0726b7eb6baafca18fe19d9e40490.png)  
 ![More positive on PC1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/4/f/4f2f69ff1d77b4cd944603b32bb3f962f1a340c0.jpeg)  
 ![Negative on PC1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/d/a/da296bb6f549d007b6d968171183fa28365ad7a2.png)  
 ![perfect SPHARM alignment](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/4/a/4aa26a4c5f3d0cddd0546ef59e744db5cad39805.png)  
 ![Positive on PC1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/1/2/12aee334ca22608d9c15ea508aaaa695f2ce7c2d.png)  
[SPHARM.vtk files](https://drive.google.com/drive/folders/1kk6pinK3_daqEJ4oklZmMwjvfcJBTryc?usp=sharing)