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Re: GRIB Aggregation



Hi Dan,

Evidently, aggregation of GRIB data may not be working. I thought since GRIB files are read by the netCDF-java library it would just work but I just heard that there may be some issues with aggregating GRIB involving how the underlying code writes indexes into the GRIB files. We'll have to wait till John is back from vacation for a more detailed answer/explanation.

Sorry for the mistake.

There currently isn't a way to have a single scan element scan a set of directories.

I believe the underlying netCDF-java code that reads GRIB files should result in fairly well-formed, CF (I think) compliant netCDF views of the dataset. Not sure how this would be affected by aggregation.

Ethan

dan.swank wrote:
Ethan:

The NARR is a reanalysis, so it don't have forecast times.  I would be a
simple 03 hr chain (00 hr fct time) spanning 26 years.

See an existing GDS subset aggregation:
http://nomads.ncdc.noaa.gov:9091/dods/NCEP_NARR_DAILY/narr-a_221_tmpprs.subset.info
This will give a sense for the nature of the beast.

The directory structure is set up as such:
http://nomads.ncdc.noaa.gov/data/narr/


Heres the TDS aggregation I set up while experimenting yesterday, on a non-related dataset:

  <dataset name="OceanWinds Test Daily Aggregation"
      ID="test/dailyagg" urlPath="test/agg">
    <serviceName>allTest</serviceName>
    <netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2";>
     <aggregation dimName="time" type="joinNew">
       <variableAgg name="wind" />
       <scan dateFormatMark="#yyyyMMdd"
location="/eclipse1a/ftp/pub/seawinds/SI/daily/netcdf/1980s/"
suffix=".nc" />
       <scan dateFormatMark="#yyyyMMdd"
location="/eclipse1a/ftp/pub/seawinds/SI/daily/netcdf/1990s/"
suffix=".nc" />
       <scan dateFormatMark="#yyyyMMdd"
location="/eclipse1a/ftp/pub/seawinds/SI/daily/netcdf/2000s/"
suffix=".nc" />
     </aggregation>
     <variable name="time" orgName="time">
       <attribute name="long_name" value="Days"/>
       <attribute name="units" value="days since 1987-07-09" />
     </variable>
    </netcdf>
  </dataset>


Would this automatically detect the source of data were GRIB rather than NetCDF? and it seems like you need to set the <scan> on each individual directory... Doing so the way NARR is set up would create one chunky configuration file. Is there anyway to have this scan a pattern (YYYYMM/YYYYMMDD) of directories?

I understand GRIB requires a certain amount of "supplemented" metadata
for complience.  Where do you enter this?

-Dan


Ethan Davis wrote the following on 6/13/2006 1:21 PM:
Hi Dan,

Aggregation should work the same for GRIB as for netCDF files. The issue
would be how your GRIB files are structured and how you want to
aggregate them. Our GRIB files each contain one full model run (all
parameters, all forecast times). We haven't tried aggregating beyond that.

We have started tracking what is available for the NCEP models on our
server. This is from the TDS 3.8 announcement (with links updated):

We also are now tracking detailed inventory of NCEP model output, eg:
http://motherlode.ucar.edu:8080/thredds/modelInventory/model/NCEP/NAM/CONUS_12km/


These are all linked from the "collection dataset" pages; For
example from
http://motherlode.ucar.edu:8080/thredds/catalog/model/NCEP/NAM/CONUS_12km/catalog.html


   choose the top "CONUS_12_km" link, then choose "Available Inventory"
   Documentation.

One idea for this work is to eventually provide access to alternate
datasets, for instance, a dataset that contains all the 3hr forecast
times from the different runs, or one that contained all the 12Z valid
times from the different runs. Tracking these detailed inventories is
just the first step but aggregation and alternate groupings of the data
is pretty interesting to think about.

How are your GRIB files structured and what kind of aggregation where
you thinking about?

Ethan

dan.swank wrote:

Hello,

I've been tinkering with the TDS aggregation capabilities and they work
quite well for NetCDF data, however, I can't seem to find anything in
the docs regarding aggregating GRIB.
We want to get The NARR dataset which we have here at NCDC-NOMADS on the
TDS.  It consists of hundreds of thousands of 50 Mb + GRIB files in a
YYYYMM/YYYYMMDD tree.
  Just scouting for a quick answer here:
Is aggregating the NARR GRIB currently feasable with the current release
of TDS?  If so, do any docs exist which could give me a starting point?
Converting it to NetCDF will not be possible (volume).



-- Ethan R. Davis Telephone: (303) 497-8155 Software Engineer Fax: (303) 497-8690 UCAR Unidata Program Center E-mail: address@hidden P.O. Box 3000 Boulder, CO 80307-3000 http://www.unidata.ucar.edu/ ---------------------------------------------------------------------------


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