common derivatives: add ACPC space label?

[yarikoptic]

• it is possible to realign using ac pc as fiducial points.
• I do not think it relates directly to any other space already listed (please correct me if I am wrong)
• there is ACPC as space for iEEG Specific Coordinate Systems
• so I think it is logical to define ACPC as a space label more generally

origin: datalad-datasets/hcp-structural-preprocessed#5

[dorahermes]

+1 on including acpc as a space

[yarikoptic]

Thank you @dorahermes . Whenever total reaches +2 (possibly accounting for -1s) I will furnish a PR ;-)

[sappelhoff]

@yarikoptic with Dora and Chris you have 2 +1s :-) given that Chris is pushing the derivatives branch now, it's probably better to furnish the PR sooner than later.

[yarikoptic]

hm, I wonder what it actually should be (standard, non-standard, nontemplate ;)) because it could be any of those depending on the definition. The use case I had in mind is HCP -- and there it seems to be not just fiducial point alignment, based on a template (MNI152), using 6DOF flirt on seems to be full brain judging from the script: https://github.com/Washington-University/HCPpipelines/blob/247ed1c3d6baf58633535c04b7e2e640673668f5/PreFreeSurfer/scripts/ACPCAlignment.sh ... so would need to check more details. Might just be claimed to be MNI152Lin.