Adding a service to a remotely served dataset
Oliver Newell
olivern at LL.mit.edu
Mon Jul 9 10:32:27 MDT 2007
Hi Roy -
FYI - We're currently experimenting with implementing WCS services, and
the same requirement (wish?) as what you're describing has been raised.
Basically, the need to discover a data set via a cataloging mechanism
(THREDDS, an OGC catalog, a DOD NCES catalog) and then be able to access
it via a WCS that resides somewhere on the network. My initial take on
it is that since WCS data access requests work with unique identifiers
(not URLs), this limits the capabilities of the service in the sense
that the Id-to-resource (data file or db) mapping is managed locally by
the WCS. In other words, the WCS has to 'know about' the resource in
advance of the request, in order to do the mapping.
I think the WCS service should support a mode of operation where a
resource's URL is included in the requests to the service, in order to
support the external WCS concept. I think it is still important to
maintain the Id as a separate entity, so it is not just a question of
using a URL for the coverage identifier, though that idea might be tempting.
The idea needs flushing out a bit, but it is still early enough in WCS's
development that changes like this can be incorporated into the spec via
the OGC working group (my opinion). It definitely seems like it would be
a useful capability to address the situation you describe.
-Oliver
Roy Mendelssohn wrote:
> Hi Glenn:
>
> No problem. But we were interested in the general problem, as there
> are other datasets which also do not have WCS and which we would like
> to add it, rather than trying to get each of them to add it (Some
> just have an OPeNDAP server, not a THREDDS server). Yours allowed me
> to give Ethan a concrete example so he could look at the catalogs.
>
> Thanks,
>
> -Roy
> On Jul 9, 2007, at 7:52 AM, Glenn.Rutledge wrote:
>
>> Hello Roy-
>> That particular dataset will be turned on shortly via WCS. That was
>> an oversight. Nice to have users telling us where we need stuff!
>> Glenn
>>
>> Ethan Davis wrote the following on 7/6/2007 6:02 PM:
>>> Hi Roy,
>>>
>>> Looks like you are referencing NCDC catalogs rather than serving the
>>> datasets yourself. So, users would get redirected to the NCDC server
>>> and access the data through the NCDC server. So, as things stand,
>>> NCDC would have to add the WCS service.
>>>
>>> You could point to each NCDC dataset with an NcML wrapper and
>>> actually serve the data from your server rather than redirecting to
>>> NCDC. If you did that, you could add the WCS service. However, the
>>> performance wouldn't be as good as direct from NCDC.
>>>
>>> I'm afraid I don't know about the WCS request for a time range. So,
>>> I'll leave that for others to answer.
>>>
>>> Ethan
>>>
>>> Roy Mendelssohn wrote:
>>>> Hi Ethan:
>>>>
>>>> I am not certain I follow. To be more specific, look at:
>>>>
>>>> http://oceanwatch.pfeg.noaa.gov/thredds/catalog.html
>>>>
>>>> and scroll down to the datasets " Remote test to Nomads THREDDS
>>>> catalog", which is actually on a THREDDS server on an NCDC
>>>> computer. They are remotely served through catalogs. Can we add
>>>> the WCS service on our end, or will it only work if NCDC adds the
>>>> WCS service.
>>>>
>>>> While I have your attention, I have not been able to get a straight
>>>> answer if there is a way to send the WCS request to get a time
>>>> range, rather than a single time, and if so what is the syntax for
>>>> that.
>>>>
>>>> Thanks,
>>>>
>>>> -Roy
>>>>
>>>> On Jul 6, 2007, at 11:24 AM, Ethan Davis wrote:
>>>>
>>>>> Hi Roy,
>>>>>
>>>>> If you are actually serving the dataset through your server (which
>>>>> it sounds like you are since you mention existing NcML for the
>>>>> dataset) rather than providing a link in your catalog to the
>>>>> remote server, I believe you can simply add the WCS service to
>>>>> your TDS configuration catalog and serve the data via WCS. It
>>>>> shouldn't require any changes to the NcML, just to the service
>>>>> element in the catalog.
>>>>>
>>>>> Of course, this depends on the dataset meeting the WCS server
>>>>> requirements, e.g., evenly spaced grid.
>>>>>
>>>>> I'm not sure how it would perform. But I'll leave it for John to
>>>>> respond on that.
>>>>>
>>>>> Ethan
>>>>>
>>>>> Roy Mendelssohn wrote:
>>>>>> Hi:
>>>>>>
>>>>>> The question for today is if our TDS is "serving" a dataset
>>>>>> remotely (ie. the remote site has their own TDS and we just link
>>>>>> indirectly to it), can we add a service to our version that they
>>>>>> don't have (just like we can aggregate a remote dataset that is
>>>>>> not aggregated). In particular the remote dataset only has an
>>>>>> OPeNDAP response, but we would like to be able to respond to both
>>>>>> an OPeNDAP and a WCS response.
>>>>>>
>>>>>> If we change our NcML appropriately, will that work?
>>>>>>
>>>>>> Thanks in advance,
>>>>>>
>>>>>> -Roy
>>>>>>
>>>>>> **********************
>>>>>> "The contents of this message do not reflect any position of the
>>>>>> U.S. Government or NOAA."
>>>>>> **********************
>>>>>> Roy Mendelssohn
>>>>>> Supervisory Operations Research Analyst
>>>>>> NOAA/NMFS
>>>>>> Environmental Research Division Southwest Fisheries Science Center
>>>>>> 1352 Lighthouse Avenue
>>>>>> Pacific Grove, CA 93950-2097
>>>>>>
>>>>>> e-mail: Roy.Mendelssohn at noaa.gov (Note new e-mail address)
>>>>>> voice: (831)-648-9029
>>>>>> fax: (831)-648-8440
>>>>>> www: http://www.pfeg.noaa.gov/
>>>>>>
>>>>>> "Old age and treachery will overcome youth and skill."
>>>>>>
>>>>>>
>>>>>>
>>>>>> ===============================================================================
>>>>>>
>>>>>> To unsubscribe thredds, visit:
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>>>>>>
>>>>>
>>>>> --Ethan R. Davis Telephone: (303)
>>>>> 497-8155
>>>>> Software Engineer Fax: (303)
>>>>> 497-8690
>>>>> UCAR Unidata Program Center E-mail:
>>>>> edavis at ucar.edu
>>>>> P.O. Box 3000
>>>>> Boulder, CO 80307-3000
>>>>> http://www.unidata.ucar.edu/
>>>>> ---------------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>
>>>> **********************
>>>> "The contents of this message do not reflect any position of the
>>>> U.S. Government or NOAA."
>>>> **********************
>>>> Roy Mendelssohn
>>>> Supervisory Operations Research Analyst
>>>> NOAA/NMFS
>>>> Environmental Research Division Southwest Fisheries Science Center
>>>> 1352 Lighthouse Avenue
>>>> Pacific Grove, CA 93950-2097
>>>>
>>>> e-mail: Roy.Mendelssohn at noaa.gov (Note new e-mail address)
>>>> voice: (831)-648-9029
>>>> fax: (831)-648-8440
>>>> www: http://www.pfeg.noaa.gov/
>>>>
>>>> "Old age and treachery will overcome youth and skill."
>>>>
>>>>
>>>
>>
>> --Glenn K. Rutledge
>> Services Team Leader
>> Remote Sensing and Applications Division
>> NOMADS Project Manager
>> National Oceanic and Atmospheric Administration
>> National Climatic Data Center
>> Asheville NC 28801
>> Phone: (828) 271-4097
>> Fax: (828) 271-4328
>>
>> NOMADS: http://nomads.ncdc.noaa.gov/
>>
>
> **********************
> "The contents of this message do not reflect any position of the U.S.
> Government or NOAA."
> **********************
> Roy Mendelssohn
> Supervisory Operations Research Analyst
> NOAA/NMFS
> Environmental Research Division
> Southwest Fisheries Science Center
> 1352 Lighthouse Avenue
> Pacific Grove, CA 93950-2097
>
> e-mail: Roy.Mendelssohn at noaa.gov (Note new e-mail address)
> voice: (831)-648-9029
> fax: (831)-648-8440
> www: http://www.pfeg.noaa.gov/
>
> "Old age and treachery will overcome youth and skill."
>
>
>
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