equipotential surfaces through WM

[jordandekraker]

made the basic functions to 1) solve a Laplace field and 2) translate surfaces inward along that field (maintining vertex correspondence)

TODO:

• [x] make sure the input volume and surface are in the correct spaces
• [x] make sure the output is in space-nativepro and with the correct tesselation (fsLR-32K vs fsnative)
• [x] make sure in 2) that the number of iterations matches the desired depth

[jordandekraker]

This is working well new as long as depths are relatively low. Greater depths will require more iterations from laplace_surf_interp.py, but running only with a few iterations for test cases highlight an issue: Green is the original surface, yellow orange and red are 0.1, 0.2, and 0.3 fractions inward surfaces. The red surface leaves little "sticks" up in gyri, which will eventually get pushed down with added iterations but the vertices below these "sticks" will be all bunched up together. I think this is still the best behaviour, since shifting all other vertices to accommodate equal face sizes would throw off the vertex-correspondence to the original surface. I just wanted to leave a note about it though.

Also @rcruces have a look at:

• [ ] pipeline integration (New module)
• [ ] New QC
• [ ] output file names
• [ ] input surface tesselations (currently fsLR-32k) and output depths (0.05, 0.1, 0.2, 0.3)
• [ ] Maybe change to native surface
• [ ] Sample all nii.gz from maps directory for all surfaces.
• [ ] in laplace_solver.py I changed the labels being used as source and sink such that the foreground (fg) is white matter only and the sink is just everything else. I thought this would be best, since now the "inner" border of white matter is actually where it ends.

Other than those, i think we're good to go here! keep me posted if anything looks funny