[MITgcm-support] possible bug in Rancic et al conformal mapping coefficients

[Stephane Popinet]

Hi Chris,

>  If I recall we actually "hard-code" a lot of the symmetry.
>  That is we generally only use the conformal mapping generated
>  coordinates from one quadrant of a cube face and then rotate
>  and translate this around the sphere. In principle I think
>  this should flag errors because grid cell coordinates would not
>  coincide.

Yes, however the group of symmetries is also used to generate the
mapping within a single quadrant (i.e. left/right, top/down and
diagonal symmetries). With the current coefficients, the mapping is
discontinuous in particular for the top/down symmetry. Again the
discontinuity is small so will not be immediately noticeable when
looking only at coordinates but it becomes obvious when e.g. computing
second derivatives.

cheers

Stephane