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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Hi all, [Sorry for cross-posting. If you access GRIB data from the TDS (THREDDS Data Server) on motherlode.ucar.edu, please read on.] We recently promoted netCDF-Java 4.3 and TDS 4.3 to be our stable releases. We are currently working on plans to upgrade the Unidata TDS [1] to run TDS 4.3. As discussed in earlier emails, this will cause the names of some variables in GRIB datasets to change. (For more details, see note [2] below.) We need help now to test the impact of these changes on you, rather than waiting until the switch is made on the production server. This change to the names of variables will require some work for users and application developers if their applications or scripts access GRIB data through the Unidata TDS especially if that access is done in a scripted manner (e.g., with variable names hard-coded in a script or persisted in some other way). To assist in this effort, the netCDF-Java library contains a mapping between old variable names and new variable names for all the NCEP GRIB model data available from the Unidata TDS. However, there is not always an unambiguous mapping from the old variable name to the new variable name. So we strongly recommend that you carefully review the new variables and select which ones you actually want to use. Examine the metadata carefully, including the time coordinate, especially if they are time intervals (e.g., an average or accumulation). These time interval variables are likely to be incorrect in 4.2. Also, please note that the variable name mapping may not be accurate for non-NCEP GRIB data. The variable name mapping information is available in an XML file in the netCDF-Java library. The netCDF-Java library also provided an API for programatic access to the variable name mapping information. (See links in [3] for documentation on the variable name mapping XML file and API.) The Unidata Test TDS [4] is currently running the latest TDS 4.3. Please test your scripts and applications against that server. The THREDDS and IDV teams are working closely to make sure the IDV can deal with this transition in a relatively seamless way (with an update to a new version of the IDV and some minimal user interaction). When opening IDV bundles that reference affected variable names, the IDV will use the netCDF-Java variable name mapping API in an attempt to find the new variable names. If that fails, the IDV will request input from the user. As described above, we recommend that IDV users manually review the new variables to make sure these are the ones you actually want to use. We plan to upgrade the Unidata TDS to 4.3 shortly after IDV 4.0 is released. We hope this will occur in the next few weeks but will provide more information on the timeline as we move forward. In the mean time, please test your scripts and tools against the Unidata Test TDS [4]. Thanks, Unidata THREDDS Team (Ethan, John, Marcos, Lansing, and Sean) Unidata IDV Team (Yuan, Julien, and Sean) ===== [1] Note on the URL for the Unidata TDS: We are deprecating http://motherlode.ucar.edu:8080/thredds/ in favor of http://thredds.ucar.edu/thredds/. The motherlode.ucar.edu:8080 URL will continue to function for now; we will stop supporting it at some point in the future. [2] CDM/TDS 4.2 uses an incorrect mapping from GRIB records to netCDF variables. CDM/TDS 4.3 has fixed the GRIB to netCDF mapping to more accurately capture the scientific meaning of the variables. This fix resulted in changes to some of the resulting netCDF variable names, descriptions, and metadata (and ended up requiring a fairly complete rewrite of the GRIB reading code). Unfortunately, the variable name changes will require some work for users and developers if their applications or scripts access GRIB data through a TDS especially if that access is done in a scripted manner (e.g., with variable names hard-coded in a script or persisted in some other way). For more details on the problem of mapping GRIB records to netCDF variables, please see: http://www.unidata.ucar.edu/staff/caron/presentations/GribNaming.pptx For details on how GRIB variables are named in CDM/TDS 4.3, please see the "Mapping a GRIB Collection into Multidimensional Variables" section of http://www.unidata.ucar.edu/software/netcdf-java/formats/GribFiles.html [3] http://www.unidata.ucar.edu/projects/THREDDS/tech/tds4.3/UpgradingTo4.3.html [4] http://thredds-test.ucar.edu/thredds/
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