Re: Client reading a catalog

Hi Tom,

Sorry again for the delayed response. I've been out of the office off 
and on all summer it seems. A better place for more timely responses 
would be our Unidata support email addresses: address@hidden 
(for general questions); address@hidden (for 
OPeNDAP/DODS questions); and address@hidden (for 
THREDDS questions); and others which you can find a list of at 
http://www.unidata.ucar.edu/support/. Cross-over questions can go to 
whichever list seems most appropriate and we'll pass it around as 
necessary. Or, another place to ask is our user lists: dods, dods-tech, 
and thredds @unidata.ucar.edu, and others also listed on our support 
page given above.

Answers inline below.

Tom Kent wrote:

> Hi Ethan,
>         I have a question about my OpenDAP client. Our software gets
> an "inventory" of netcdf filenames for a given model that is selected.
> Basically, it does a readdir on a data disk that is mounted locally and
> gives us a list of file names such as:
> 20060713_1200
> 20060713_0000
> 20060712_1200
> etc...
> This list is then used to time-match what the user is looking for and the
> specific file wanted is then accessed locally with netcdf calls.
>
> We need to duplicate this when accessing data remotely using OpenDAP
> and since we can't do an "ls" or "readdir" we have to find a different way.
> I'm able to access a specific netcdf file and get the data correctly using
> the URL like this in the client software (e.g):
> http://px1-alps/dap/nph-dods/cdf/CONUS211/Eta/20060717_0000
> But I had to hardwire a specific filename to do this.
>
> I'm also able to generate catalogs dynamically on the server side (e.g.):
> http://px1-alps:8080/thredds/catalog/cdf/CONUS211/Eta/catalog.html
>
> How do I get (access...read-in...) the output of the catalog within my client
> remotely? I'd like to just parse the xml catalog output for the dataset name 
> lines and
> get the list of filenames from there if possible. Or maybe there's some other
> easy way to do this. I realize the netcdf client libs are what make it possible 
> to
> access the netcdf data remotely. But the catalog output is not netcdf so I'm
> not sure how to set up my software to import it's results for parsing. I didn't
> see any client apps that referred to xml files.
>
> Basically I'd like what I get for this url:
> http://px1-alps:8080/thredds/catalog/cdf/CONUS211/Eta/catalog.xml
> to be read into some buffer in my remote client software so I can parse it.
> Is this possible? I apologize if this is something really simple but I'm a 
> rookie
> with this stuff. I looked on the msg boards and didn't see anything related.
> Thanks for any info!
>  
The THREDDS Java client libraries are available for reading and dealing 
with THREDDS catalogs from the THREDDS web page 
(http://www.unidata.ucar.edu/projects/THREDDS/). In the "Getting 
Started" section, there's a "THREDDS Java Client Libraries" link that 
takes you to a page on that.

Java is our initial development environment and we don't have the 
resouces to develop in multiple languages at this point. So, if you are 
not able to use Java in your application, you'll have to find an XML 
parser for your environment and interpret the THREDDS catalogs yourself. 
The THREDDS catalog spec is available at 
http://www.unidata.ucar.edu/projects/THREDDS/tech/catalog/InvCatalogSpec.html.

I'm not really familiar with non-Java XML parsers but I know there are 
lots out there.

Hope this helps. Let us know how it goes.

Ethan

> Tom Kent
> Information Systems Branch
> GSD/ESRL/NOAA
>
>  

--
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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