[CF-metadata] UTM projections

[John Caron]

How do people feel about adding Universal Transverse Mercator (UTM) as a 
Grid Mapping? We are talking to someone who wants to use UTM, and we'd 
like to steer them to CF.

As I understand it, UTM uses the ellipsoidal Transverse Mercator 
projection The earth is divided up into approximately 60 x 24 "zones", 
each with specific projection parameters. There are a number of 
complications, like the fact that the reference ellipsoid may differ 
between zones, and near the poles it in fact switches to a polar 
stereographic projection.

All of this complicates the client that has to implement it, but in 
terms of CF coding it would be just a matter of specifying the UTM zone, eg:

grid_mapping_name = UTM

Map parameters:

zone - eg "13T"

A client has to have a table that maps the zone name into the right 
Transverse Mercator (or Polar Stereographic) projection parameters. The 
alternative would be to make the user use the Transverse Mercator (or 
Polar Stereographic) projection directly, and figure out the right 
paramters themselves.