[netcdfgroup] Correction: Access to coordinate variables using nc-dap or netcdf

• To: Dennis Heimbigner <dmh@xxxxxxxxxxxxxxxx>
• Subject: [netcdfgroup] Correction: Access to coordinate variables using nc-dap or netcdf
• From: Dennis Heimbigner <dmh@xxxxxxxxxxxxxxxx>
• Date: Tue, 02 Feb 2010 13:50:33 -0700

Let me add a correction to my previous message.
To be precise, the issue is not with either Hyrax
or Thredds. Rather it is with the code which translates
netcdf files to DAP format.  This code is, I believe,
a plugin module in the servers. What you see will depend
on this plugin, not on the server per se.

=Dennis Heimbigner


Dennis Heimbigner wrote:

The situation is as follows:

1. The original nc-dap code makes invisible any
   coordinate variables that are mapped to
   OPeNDAP map variables inside Grids.
   The netcdf code mimics that behavior.

2. Different OPeNDAP servers translate netcdf files to
   the DAP format in different ways ( I just did the test
   to verify this).

   a. Hyrax servers place coordinate variables inside Grids
      as map variables.  This means (per #1) that they
      are invisible to clients.

   b. Thredds servers duplicate the coordinate variables
      so that they are outside of the Grids and hence those
      coordinate variables are visible.

3. When serving up non-netcdf files, the translations
   may or may not place the equivalent of coordinate variables
   either inside Grids or outside. See for example:
       http://tds.hycom.org/thredds/dodsC/glb_current_analysis

Personally, I think that the Thredds translation is preferable
to the Hyrax translation, but that is just me :-)

In any case, the problem is not with the clients, but rather with
the servers. Perhaps the community can come to some resolution on this.

Also, as I mentioned in another message, there is an alternative:
If you have compiled netcdf using --enable-netcdf4, then you can
do an ncdump -k3 and it will present the DAP data in netcdf-4 format,
and in that format, everything is visible.

=Dennis Heimbigner


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• References:
  • Re: [netcdfgroup] NetCDF 4.1-beta and OPeNDAP/coordinate variable question
    • From: David Brown
  • [netcdfgroup] Access to coordinate variables using nc-dap or netcdf
    • From: Dennis Heimbigner