Prevent Transformix from writing output image if output volume node note given

[prash-p]

Pull request in response to this discussion https://discourse.slicer.org/t/prevent-transformix-running-in-slicer-elastix/7902

[lassoan]

Does this work? If you don't run transformix then what would generate deformationField.mhd?

I think we need to implement a reader for elastix transformation files as I described it here.

[prash-p]

It works on the data I had to test on. Transformix still runs to produce the deformation field, but the input parameters are altered so an output image isn't created if not required. This can save a little bit of time at the end of the registration process.

I agree the ideal situation would be to convert the proprietary transforms into a slicer transform, instead of running transformix. I'll take a look at your work on it and see if I can contribute in any way.

[lassoan]

OK, I see, so we run transformix anyway, but we don't generate resampled output volume if we don't need it.

Could we simply make inputParamsTransformix += ['-in', os.path.join(inputDir, 'moving.mha')] conditional (only add it if resampled moving volume is needed) instead of duplicating about 20 lines of code?

This change will help a bit, but implementing transform reader would make a huge difference: we could get the transform in seconds (immediately if only linear) and store it in a few kilobytes instead of hundreds of megabytes.

[prash-p]

Yes that would work I think, but we need to consider the condition when the user wants an output volume but no transformation. In this case we could just not create an output transform node?

[lassoan]

Yes, we need to handle volume, transform, and volume+transform cases, preferably with a single call of transformix (just by tuning its command-line arguments).

[prash-p]

Do you want me to make those changes, or are you working on it?

[lassoan]

Please make the changes. Thank you!

[prash-p]

Should work same as before but with fewer lines now.