Hi David,
A while back there was discussion on the mailing list regarding the
addition of two new attributes to the CF convention to record the
min/max values of a variable in a generic way. See
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2008/002191.html
I have a vague recollection that this proposal made it through to a CF
trac ticket. However, I don't see the new attributes in the latest CF
conventions document, and unfortunately I'm not currently able to check
the CF trac site because it's throwing an 'invalid security certificate'
error in my browser. You may have more luck.
But, in principle, I reckon those two new attributes, if/when added to
CF, would provide you with a workable solution, e.g. something like...
double x(x);
x:standard_name = "projection_x_coordinate";
x:units = "m";
x:actual_min = 0.0; // or whatever value is appropriate
x:actual_max = 12345678.0; // ditto
...
Similarly for y.
HTH,
Phil Bentley
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu
> [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of David Fanning
> Sent: 22 January 2010 17:50
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Description of Map Projection Grid
>
> 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
>
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Received on Mon Jan 25 2010 - 03:27:33 GMT
