PCA Multidomain Analysis - Question

[MLopezPon]

Good morning. I was doing a multi domain analysis and I was trying to understand how to analyze the PCA depending on parameters using studio.

I am not sure to completely understand the "alignment reference domain"
Is it the PCA done based on the gravity center of the “assembly” vs each domain?

[akenmorris]

Hopefully this explains it:

http://sciinstitute.github.io/ShapeWorks/latest/studio/multiple-domains.html#multiple-domain-alignments

When there are multiple anatomies, there are options to choose how to analyze the articulation (relative position) of the different anatomies across subjects.

In the example on that page, when you set the pelvis as the reference domain, then one mode of variation within the multi-domain model is the relative position of the femur. If you choose femur instead, you'll see the femur stay in basically the same position and the femur moves around it. It's a frame of reference.

There is also the option to use the "global alignment", which is generally determined at groom time by using an ICP registration on the combination of all anatomies for each subject.

There is also the option to use the "local alignment", which ignores articulation and you'll see each anatomy more or less on their own.

Besides these options, there is also the multi-level PCA which can separate out shape and relative pose.