[CF-metadata] Description of Map Projection Grid

[David Fanning]

Folks,

I have searched the list archives, but have not found a solution to my problem.

I have map projected images I wish to package in a netCDF file. Along with
other map projection information, I would like to describe the extent of the
map projection grid that is associated with the image. This is an XY grid,
normally expressed in meters. Knowing the extent of this grid is important
for navigating the image, adding image annotations, and other things.

In GDAL the grid extent is sometimes expressed as the Northernmost_Northing,
the Southernmost_Northing, the Easternmost_Easting, and the 
Westernmost_Easting.
These names would mean something if my map projection was, for example,
a Mercator projection of the entire Earth. But my map projections are 
polar projections,
and so this terminology is misleading, to say the least. If the image in is the
southern hemisphere, the terminology is bizarre.

What I am looking for are standard names to define the extent of this
XY grid. I have found in the CF 1.4 standard the names 
"projection_x_coordinate"
and "projection_y_coordinate". This is getting to what I am looking
for, but there is no supporting documentation to tell me exactly which point
on my projection grid these names are describing. (I would guess this could
describe the upper-left corner of the grid, or what would be called 
the "tie-point"
in a GeoTIFF file, for example, but I am not sure.)

Does anyone have any experience describing this XY grid? Or can anyone
suggest a standard name I have overlooked?

I think these names could be possibilities:

    projection_x_coordinate_minimum
    projection_x_coordinate_maximum
    projection_y_coordinate_minimum
    projection_y_coordinate_maximum

Thank you for your help.

Cheers,

David

--------
David W. Fanning
Scientific Programmer
NSIDC/CIRES, Univ. of Colorado
E-Mail: fanning at nsidc.org