common coordinate for hippocampal surface data

[jordandekraker]

After talking to @lzehl, I would like to create a common coordinate for hippocampal surface data derived from HippUnfold and used in HippoMaps.

One issue that I anticipate is that there are actually four different "densities" of canonical (folded/unfolded) hippocampal spaces. These densities are interchangeable, and can be found here (all _midthickness.surf.gii files).

I will follow up with additional details when I have more time available.

[lzehl]

@jordandekraker thank you for raising the issue. We are looking forward to integrate this common coordinate space for the hippocampus. @tgbugs and @UlrikeS91 we should have a look already on the information available and discuss this contribution.