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[THREDDS #FUB-114946]: Understanding vertCoord behaviour with netcdf subset service

Hi Daryl,

I started to take a look at the phenomenon you are seeing, but I immediately 
noticed that the Thredds server you've referenced is running a very old version 
of the TDS - 4.2.10 from April of 2012.  We've done a lot of work since then, 
and there is a reasonable good chance that a bug contributing to the behavior 
has been fixed in a subsequent version of the TDS.

Any chance you can convince them to upgrade?  We're gone all the way through 
4.3.20, and are about to release 4.4.0.

  Lansing Madry
  Boulder, Colorado

> Hi Thredds Dudes,
> I was recently exchanging emails with NCDC about their thredds server and
> how it was handling vertCoord requests for the netcdf subset service.  I
> am really confused by the behaviour and perhaps there are bugs afoot here!
> Lets start this goose chase with the documentation:
> http://www.unidata.ucar.edu/software/thredds/current/tds/interfaceSpec/NetcdfSubsetService_4_3.html#Vertical
> "Subset on the vertical axis of a variable or variables with the same
> vertical levels may be done with the vertCoord parameter"
> Okay, so if I go here:
> http://mtarchive.geol.iastate.edu/thredds/ncss/grid/mtarchive/2013/11/04/gempak/model/2013110412_avn211.gem/pointDataset.html
> and put in '2' for the vertical level and TMPK_HGHT var, I get
> http://mtarchive.geol.iastate.edu/thredds/ncss/grid/mtarchive/2013/11/04/gempak/model/2013110412_avn211.gem?var=TMPK_HGHT&latitude=41.99&longitude=-93.61&temporal=all&time_start=2013-11-07T18%3A00%3A00Z&time_end=2013-11-14T12%3A00%3A00Z&time=2013-11-07T18%3A00%3A00Z&vertCoord=2&accept=csv&point=true
> lots of NaN !  Hmmm, if I change, vertCoord to blank
> http://mtarchive.geol.iastate.edu/thredds/ncss/grid/mtarchive/2013/11/04/gempak/model/2013110412_avn211.gem?var=TMPK_HGHT&latitude=41.99&longitude=-93.61&temporal=all&time_start=2013-11-07T18%3A00%3A00Z&time_end=2013-11-14T12%3A00%3A00Z&time=2013-11-07T18%3A00%3A00Z&vertCoord=&accept=csv&point=true
> still NaN...  If I then change vertCoord to 0, I get data!
> http://mtarchive.geol.iastate.edu/thredds/ncss/grid/mtarchive/2013/11/04/gempak/model/2013110412_avn211.gem?var=TMPK_HGHT&latitude=41.99&longitude=-93.61&temporal=all&time_start=2013-11-07T18%3A00%3A00Z&time_end=2013-11-14T12%3A00%3A00Z&time=2013-11-07T18%3A00%3A00Z&vertCoord=0&accept=csv&point=true
> but then if I add UREL_HGHT
> http://mtarchive.geol.iastate.edu/thredds/ncss/grid/mtarchive/2013/11/04/gempak/model/2013110412_avn211.gem?var=TMPK_HGHT&var=UREL_HGHT&latitude=41.99&longitude=-93.61&temporal=all&time_start=2013-11-07T18%3A00%3A00Z&time_end=2013-11-14T12%3A00%3A00Z&time=2013-11-07T18%3A00%3A00Z&vertCoord=0&accept=csv&point=true
> I get data, but the vertCoord[unit="m"] is now zero for everything.
> Looking back at the documentation, it has:
> Request: "Give me variable Temperature_pressure at a particular vertical
> level: 1000 mb*"
> Temperature_pressure                                          1000
> ?var=Temperature_pressure&vertCoord=1000
> so it would appear vertCoord is the value along the vertical axis and not
> the index along the axis?
> Any thoughts on this?  I understand that this is very complex problem to
> account for.
> thanks,
> daryl
> --
> /**
> * Daryl Herzmann
> * Assistant Scientist -- Iowa Environmental Mesonet
> * http://mesonet.agron.iastate.edu
> */

Ticket Details
Ticket ID: FUB-114946
Department: Support THREDDS
Priority: Normal
Status: Open

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