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I have seen the following example to access a netcdf file using excel.

I was wondering if it possible to access a certain part of the data based on specific indices (e.g. a time series of a parameter at a certain point on a map from a 4D variable)

It seems to me like it would not be possible without any coding?

Any thoughts?

Julien Chastang
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ZZZ
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1 Answers1

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There are two ways I know of to access data from Unidata's THREDDS Data Server using Excel:

1) Extract a time series is using the ASCII response from OpenDAP as described here: https://publicwiki.deltares.nl/display/OET/OPeNDAP+access+with+Excel. This approach will work with any OPeNDAP server.

2) Use the NetCDF-Subset Service provided by the THREDDS Data Server (here I'm using the latest TDS, version 4.3).

So if you go to a particular dataset served by THREDDS, like this one:

http://geoport-dev.whoi.edu/thredds/catalog/coawst_2_2/fmrc/catalog.html?dataset=coawst_2_2/fmrc/coawst_2_2_best.ncd

and click on the NetcdfSubset service, and then "Grid as Point Dataset", you get this form:

http://geoport-dev.whoi.edu/thredds/ncss/grid/coawst_2_2/fmrc/coawst_2_2_best.ncd/dataset.html

where you can extract a time series closest to a particular location, and choose CSV as the output type, which can of course be easily loaded into Excel. The nice thing is this form just generates a RESTful URL query, which can be modified or easily generate by code. So for example, this query extracts a time series for the variable temp over a 6 hour interval near the surface and closest to -70.6W, 42.3N:

http://geoport-dev.whoi.edu/thredds/ncss/grid/coawst_2_2/fmrc/coawst_2_2_best.ncd?var=temp&latitude=42.3&longitude=-70.6&time_start=2011-08-01T00%3A00%3A00Z&time_end=2011-08-01T06%3A00%3A00Z&vertCoord=-.03&accept=csv

produces:

    date,lat[unit="degrees_north"],lon[unit="degrees_east"],vertCoord[unit=""],temp[unit="Celsius"]
2011-08-01T00:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.44405174255371
2011-08-01T01:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.361846923828125
2011-08-01T02:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.31492805480957
2011-08-01T03:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.254281997680664
2011-08-01T04:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.24005889892578
2011-08-01T05:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.186853408813477
2011-08-01T06:00:00Z,42.31439418116631,-70.58628311827651,-0.03125,18.114046096801758

Documentation on the NetCDF Subset Service is here: http://www.unidata.ucar.edu/projects/THREDDS/tech/interfaceSpec/NetcdfSubsetService_4_3.html#Vertical

There are a few issues with vertical coordinate in the NetCDF Subset Service that I have reported to Unidata:

  1. In previous versions of the TDS there was a selection on the web to specify vertical level. This seems to have gone missing in the latest version of the TDS (4.3.15). So if don't see the vertical level specifier, you can still specify a certain level by adding it manually to the URL.
  2. The vertical selector works fine for data with dimensional coordinaets, but For dimensionless vertical coordinate models, even if they are CF-Compliant, the service is currently is not converting to dimensional coordinates. So the user receives the dimensionless coordinate back, and also must specify the dimensionless coordinate if they want a particular level. This is obviously not very useful.
  3. If the user specifies a level above or below the levels in the dataset, the data value that is returned is a NaN. So for an ocean model, if you enter a value of 0, thinking that you will get the surface layer, you might get a NaN, because the level of the surface layer might be -0.03 or something (as in the example above).

I have reported all of these issues to Unidata.

Rich Signell
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