To this topic a tip from Matthias:
https://doi.org/10.1088/1361-6587/ac5f3f
Radial coordinate maps, radial vectors, and binormal vectors for 5/6, 5/5 and 5/4 edge island domains in W7-X
J C Schmitt, D M Kriete, T Andreeva, J Geiger, M Grahl, J Schilling, H Thomsen and E Flom
Published 20 April 2022 • © 2022 Max-Planck Institute for Plasma Physics
Plasma Physics and Controlled Fusion, Volume 64, Number 5
Citation J C Schmitt et al 2022 Plasma Phys. Control. Fusion 64 055022