[CF-metadata] HDF swatch

[Jonathan Gregory]

Dear Bob

> auxiliary coordinate variables must have the same size dimensions as their
> corresponding data variables, so there's no way to translate a Swath to
> CF-compliant netCDF without expanding and interpolating the gelocation
> variables to make them match the data dimensions.

I think that's right. We wanted software to be able to locate the data without
having to do any calculation of coordinates. If you want the transformation to
be reversible I suppose you could include some attributes of your own definition
to record which points in the coordinate data to discard when going to HDF.

Best wishes

Jonathan