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>To: address@hidden >From: "Ze'ev Gedalof" <address@hidden> >Subject: Perl, Coordinate Variables >Organization: University of Victoria Tree-Ring Laboratory >Keywords: 199909162334.RAA27466 netCDF Perl coordinate variable conventions Hi Ze'ev, > I am a new NetCDF user (using the Perl extension), and am a little > perplexed by the definition of coordinate variables given in the version 2 > and 3 guides. I am working with gridded climate data (SLP and SST) which I > would like to coordinate by lat, long, and time. I think that I have > managed to create these variables as coordinate variables (ncdump -c lists > them as such), but I can't figure out how to use them now. Is there a more > extensive definition somewhere of what coordinate variables are and how to > use them? In terms of the netCDF library, coordinate variables are merely a convention that applications are free to use or ignore. Some applications use coordinate variables in accessing and subsetting data; others require that you use indices, so you need to write a layer to translate coordinate variable values into indices. For climate data, probably the most elaborate conventions for coordinate variables are documented in "GDT netCDF conventions for climate data, version 1.3" available from http://www-pcmdi.llnl.gov/drach/GDT_convention.html There has been extensive discussion on the netcdfgroup mailing list of how to strengthen the coordinate variable conventions to make them more useful, and of whether multidimensional coordinate variables should be supported. To browse some of these discussions and the proposals that resulted from them, see http://www.unidata.ucar.edu/packages/netcdf/coords/proposals.html and http://www.unidata.ucar.edu/packages/netcdf/coords/ While there were several good proposals, no consensus was achieved by the discussions, so you are free to pick your own extended coordinate variable conventions. Unfortunately, none of these conventions are supported by all netCDF software, though there is good support for use of coordinates in the FAN package and a few others, accessible from the "Software for Manipulating or Displaying NetCDF Data" document at http://www.unidata.ucar.edu/packages/netcdf/software.html --Russ _____________________________________________________________________ Russ Rew UCAR Unidata Program address@hidden http://www.unidata.ucar.edu