# Particles do not move during optimisation

**URL:** <https://shapeworks.discourse.group/t/particles-do-not-move-during-optimisation/398>\
**Category:** Uncategorized\
**Created:** [March 12, 2026, 6:12pm UTC](https://shapeworks.discourse.group/t/particles-do-not-move-during-optimisation/398 "2026-03-12T18:12:09Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![SLaranjeira](https://avatars.discourse-cdn.com/v4/letter/s/5f8ce5/32.png) [@SLaranjeira](https://shapeworks.discourse.group/u/SLaranjeira)\
**Post date:** [March 12, 2026, 6:12pm UTC](https://shapeworks.discourse.group/t/particles-do-not-move-during-optimisation/398/1 "2026-03-12T18:12:09Z")

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Hello,

I am developing a model that requires rigid registration of meshes based on the registration transform of CT images.  
I create a transform from the registered CTs, and then I apply that transform to the corresponding meshes.  
I save the transform as the grooming transform in a project .xcel file.  
When I move to the optimising stage, the particles do not move during the iterations per split, only moving in the optimisation iterations. The result is that the particles cover most of the shape, but there is no correspondence between shapes.  
If I start the process over and take as initial input shapes the groomed shapes, skip grooming, the optimisation output is great.  
So I do not understant what is the difference between the two cases. Is my registration transform introducing errors?  
I understand that my question is quite vague, so please let me know which files would be helpful for me to share.  
Any help would be really appreciated.

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**Author:** ![amorris](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@amorris](https://shapeworks.discourse.group/u/amorris)\
**Post date:** [March 17, 2026, 3:54pm UTC](https://shapeworks.discourse.group/t/particles-do-not-move-during-optimisation/398/2 "2026-03-17T15:54:36Z")

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The difference is likely the alignment. If the shapes are not properly aligned, then during the initialization phase, the mean force used for correspondence may constrain the particles to a small location on each shape (the average position). Once it moves to optimization, the mean position force is no longer used and the covariance based objective is used.

A good initialization is generally necessary to achieve good correspondences, so the alignment issues should be resolved first.

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<div class="post-metadata">

**Author:** ![SLaranjeira](https://avatars.discourse-cdn.com/v4/letter/s/5f8ce5/32.png) [@SLaranjeira](https://shapeworks.discourse.group/u/SLaranjeira)\
**Post date:** [March 18, 2026, 3:05pm UTC](https://shapeworks.discourse.group/t/particles-do-not-move-during-optimisation/398/3 "2026-03-18T15:05:50Z")

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Hello Allen Morris,  
Thank you very much for your prompt response.  
Your diagnosis was completely correct.  
My problem was that I was storing the groomed meshes after applying the registration transform, and they should have been saved before. This resulted in the groomed meshes being interpreted as being in a different space.  
Now corrected everything seems to be working properly.  
Thank you again,  
Best wishes,  
Simão