afni.nimh.nih.gov

You may want to take a look at the script in this previous thread that includes an example ccalc command to include distance.
https://afni.nimh.nih.gov/afni/community/board/read.php?1,160717,160746#msg-160746

For some ideas on picking representative locations, see this poster:
https://afni.nimh.nih.gov/pub/dist/HBM2020/GlenEtal_FindingYourCenter_OHBM2020.pdf