Slicer uses VTK’s transform classes, which are far more versatile than ITK (SimpleITK):
- you can concatenate arbitrary chain of forward/inverse transforms and VTK can apply it to objects dynamically
- VTK transforms provide transformation on the entire 3D space (while in ITK transforms, displacement drops to 0 outside the specified domain)
- VTK ensures displacement is smoothly converging 0 or constant outside the specified domain, which allows robust inverse computation.
If you need an inverse transform that ITK can use, you can convert the transform to a displacement field (in Transforms module / Convert section).