Order of transform

[rprueckl]

Hi - I have a similar problem as already described (but unanswered) in this post:

In my application, the transform hierarchy for a moving volume is as follows:

W = Tbs ° Taff ° Tinit

W ... world
Tbs ... bspline transform
Taff ... affine transform
Tinit ... initial transform

Tbs and Taff are initially identity. The user through the UI manually edits Tinit. It is used as initial transform for elastix.

Now, I use Elastix with affine and bspline registration. I thought I could put the resulting affine and bspline transform to Taff and Tbs respectively. However, this leads to incorrect results. Instead, what comes out is the following transform hierarchy:

W = Tinit ° Taff ° Tbs

This is counterintuitive for me and also difficultly usable in my workflow.
Why is that so and how can I correct for this in order to get the correct transform hierarchy?
Using Elastix 5.1.0

Thanks