[MITgcm-devel] possible issue with exf interp defaults

[gael forget]

Dear All,

I recently ran into trouble by assuming that the climsst_interpMethod default was 0 (i.e. "no interpolation" unless explicitly 
specified in data.exf) and providing a relaxation field that was already on the LLC90 grid (in the 90x1170 “compact” format).

I see now that a different default was chosen and that climsst_lon0, climsst_inc, etc. by default get assigned to:
      inp_lon0 = xgOrigin + delX(1)*exf_half
      inp_lat0 = ygOrigin + delY(1)*exf_half
      inp_dLon = delX(1)
      inp_dLat = delY(1)

I think, and Jean-Michel seemed to concur, that in the case of a simple lat-lon grid these defaults yield an interpolation 
from XC, YC to XC, YC itself (i.e. kind of "no interpolation" but maybe not quite). However, unless I am missing 
something obvious, this approach can lead to rather strange results for pretty much any other grid. 

Wouldn't one of the two following approaches make more sense:
- set interpMethod defaults to 0 at least with usingCurvilinearGrid or rotateGrid?
- set the lon0, inc, etc defaults to UNSET_RL and stop if the user did not define them in data.exf?

Please chime in.

Thanks,
Gael
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