This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
Hi Don: We will have a look to see if we can safely disambiguate the conflicting info. Can you contact CDO and let them know they have a bug? thanks John > Dear Lansing, John and Ethan- > > Thanks for your responses. I had read the CF conventions about the > standard names and understand that grid_latitude/grid_longitude are the > standard names for a rotated pole projection. That's why I indicated to > Lansing that this was the problem. > > However, as Ethan points out, the units are wrong for a rotated_pole and > there is no grid_mapping_name variable associated with the tas variable. > So, tas is not defined by a rotated pole coordinate system. > > The original grid is a gaussian dataset and the original standard names > were latitude and longitude, so CDO does change the standard names. > > From my perspecitve, though, the latitude and longitude variables meet > the requirements for being standard latitude and longitude variables in > CF by the units and axis attributes: > > http://cfconventions.org/1.6.html#latitude-coordinate > > (correct units and axis attributes) much more than for the rotated pole > case (wrong units, no grid_mapping_name). So, I would still content > that this is a bug. > > Don > > On 5/16/14 4:43 PM, Unidata netCDF Java Support wrote: > > Hi Don, > > > > The use of "grid_latitude" and "grid_longitude" standard names indicates a > > rotated pole grid mapping (defined in Appendix F: "Grid Mappings" section > > [1] of the CF spec). But lat and lon have the wrong units for a rotated > > pole grid (they should be "degrees") and a rotated pole grid mapping is not > > defined. (Here's the definition for "grid_latitude" [2] from the CF > > standard name table [3].) > > > > Was the original dataset on a rotated pole grid? > > > > Ethan > > > > [1] http://cfconventions.org/1.6.html#appendix-grid-mappings > > > > [2] "Latitude is positive northward; its units of degree_north (or > > equivalent) indicate this explicitly. In a latitude-longitude system > > defined with respect to a rotated North Pole, the standard name of > > grid_latitude should be used instead of latitude. Grid latitude is positive > > in the grid-northward direction, but its units should be plain degree." > > > > [3] https://badc.nerc.ac.uk/help/formats/netcdf/cf-standard-name-table.html > > > > Don Murray wrote: > >> It doesn't like the standard_name for latitude and longitude (using ncml > >> to remove them makes the grid readable). I don't have the ability to > >> remove them in the workflow, and this seems like a bug. > >> > >> Don > >> > >> On 5/16/14 3:35 PM, Unidata netCDF Java Support wrote: > >>> There's confusion somewhere, ToolsUI is looking for a projection instead > >>> of recognizing the lat lon coords. > >>> > >>> -Lansing > >>> > >>> On 5/16/2014 12:55 PM, Don Murray (NOAA Affiliate) wrote: > >>>> New Ticket: why can't this be read as a grid > >>>> > >>>> Hi- > >>>> > >>>> I have a netCDF file that I created using the Climate Data Operators > >>>> (CDO) package by subsetting a larger file. The original file can be > >>>> read into the IDV/ToolsUI, but the subset cannot (is not recognized as a > >>>> grid). I don't see anything obviously wrong with the file, except that > >>>> maybe the CDM is getting confused by the use of x and y? > >>>> > >>>> Why doesn't the CDM recognize this as a grid? > >>>> > >>>> Don > > > > > > Ticket Details > > =================== > > Ticket ID: RIZ-451320 > > Department: Support netCDF Java > > Priority: Normal > > Status: Closed > > > > -- > Don Murray > NOAA/ESRL/PSD and CIRES > 303-497-3596 > http://www.esrl.noaa.gov/psd/people/don.murray/ > > Ticket Details =================== Ticket ID: RIZ-451320 Department: Support netCDF Java Priority: Normal Status: Open