OPeNDAP Access to GLBy0.08/expt_93.0 Hindcasts vs FMRC

[James Polly]

Hello!

I am successfully able to open GLBy0.08/expt_93.0 datasets from forecast (FMRC) using python tools like siphon and xarray which leverage OPeNDAP to access.

The THREDDS catalog URL I use for FMRC is:

https://tds.hycom.org/thredds/catalog/GLBy0.08/expt_93.0/FMRC/runs/catalog.xml

You can see the catalog above from the directory structure at this link: https://tds.hycom.org/thredds/catalogs/GLBy0.08/expt_93.0.html

I would like to achieve the same functionality for hindcast data.

When I attempt to access the hindcast data using a URL like the one below, I get an error indicating that OPeNDAP is not supported.

https://tds.hycom.org/thredds/catalog/datasets/GLBy0.08/expt_93.0/data/hindcasts/2018/catalog.xml

The XML content at the above link contains OPENDAP settings in the same way that the FMRC URL shown above does.

Any help is appreciated! Thanks very much for your time!

James

[Michael McDonald]

James,
Is your application(s) "thredds catalog" (.xml URLs) aware or is it
"opendap" aware, or is it both?

You did not include any "OPENDAP" URLs. You point to different catalog
listings that have *several datasets* available within them. So likely
the methods for *selecting the correct dataset* from the catalog in
your code is where things are going wrong. I only have experience with
using this browse method in GUI applications like NASA's Panoply where
you can open a "catalog URL", but end up with an "OPENDAP" URL in the
end for visualizing.


e.g., if you want the latest FMRC for the global ocean model then
simply use this OPENDAP URL (and you are done). Plug this into any
opendap aware application. Unless you care about the specific forecast
run that adfta came from, then I would recommend the use of the "FMRC
Best".

https://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0/FMRC/GLBy0.08_930_FMRC_best.ncd

* this "Data URL" is available on the "OPeNDAP Dataset Access Form"
page or in the previous page listing the "Access:" methods supported
for the specific dataset.
e.g., https://tds.hycom.org/thredds/catalog/GLBy0.08/expt_93.0/FMRC/catalog.html?dataset=GLBy0.08/expt_93.0/FMRC/GLBy0.08_930_FMRC_best.ncd


if you want the older hindcast/non-forecast data from the same model
then you can use any of the access methods here:

https://tds.hycom.org/thredds/catalogs/GLBy0.08/expt_93.0.html?dataset=GLBy0.08-expt_93.0

e.g., OPENDAP
https://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0


$ ncdump -h 'https://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0/FMRC/GLBy0.08_930_FMRC_best.ncd'
| head
netcdf GLBy0.08_930_FMRC_best {
dimensions:
depth = 40 ;
lat = 4251 ;
lon = 4500 ;
time = 101 ;


$ ncdump -h 'https://tds.hycom.org/thredds/dodsC/GLBy0.08/expt_93.0' | head
netcdf expt_93 {
dimensions:
depth = 40 ;
lat = 4251 ;
lon = 4500 ;
time = 14001 ;

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Michael McDonald
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[James Polly]

Michael, thank you very much for the helpful response.

The application I'm using (Unidata's Siphon) is both THREDDS Catalog and OPeNDAP aware.

Your suspicion of where the problem is occurring seems to be correct. I've identified this same problem with the Siphon maintainers and it appears to be a problem with the way that the tool takes the catalog listing and finds the (e.g. OPeNDAP) access URL.

I'll follow up here with what happens. Again, I really appreciate your time and consideration.