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Combining THREDDS and Pydap services
- Subject: Combining THREDDS and Pydap services
- Date: Mon, 27 Nov 2006 17:43:43 -0800
Title: Combining THREDDS and Pydap
services
I apologize for the double post. I got my mail lists
confused (old age is setting in), I originally posted to
support-thredds but meant to post it here.
-Roy M.
Hi:
I am throwing out to the list a THREDDS related server problem
that we are trying to figure out relatively clean ways to solve, in
the hope that others may have some good ideas on how to accomplish
this.
We are heavily invested in THREDDS
(http://oceanwatch.pfeg.noaa.gov/thredds/catalog.html) in particular
the cataloging and the data aggregation. Most of the links on
that page are not single files but many files (sometimes in the
thousands) being aggregated through time. This is a very useful
feature for the type of data we have.
Also, on an in-house server we have been testing Roberto De
Almeida's pydap implementation of OPeNDAP (http://pydap.org/).
This server has a lot of nice features that we are interested in, such
as his wms service and kml service from an OPeNDAP URL type
_expression_.
So what is the issue. Clearly, on web pages that are
developed in house, where a user just clicks on a link, if we have
both Pydap and THREDDS running on the same machine, we can change the
links to point to the appropriate server. But for the more general
public, or for people using the links in scripts etc, we would like to
have just one basic link that depending on the file ending would
go to the correct place.
So right now if I wanted the second time period, full extent of
one of the files the URL would be:
http://oceanwatch.pfeg.noaa.gov/thredds/dodsC/satellite/AT/ssta/1day?ATssta[1:1:1][0:1:0][0:1:2320][0:1:3200]
If I wanted an ascii file it would be:
http://oceanwatch.pfeg.noaa.gov/thredds/dodsC/satellite/AT/ssta/1day.ascii?ATssta[1:1:1][0:1:0][0:1:2320][0:1:3200]
but what I would like to do is that if I give it:
http://oceanwatch.pfeg.noaa.gov/thredds/dodsC/satellite/AT/ssta/1day.kml?0:1:2320][0:1:3200]
and it would know to switch-over to the pydap server and produce
the kml output (while still being able to view the file as a single
file through the THREDDS aggregation).
Now as given, it is unlikely to work since THREDDS is in the
URL. But suppose we had something like:
http://oceanwatch.pfeg.noaa.gov/ERD_Data/satellite/AT/ssta/1day.ascii?ATssta[1:1:1][0:1:0][0:1:2320][0:1:3200]
or
http://oceanwatch.pfeg.noaa.gov/ERD_Data/satellite/AT/ssta/1day.kmlATssta[1:1:1][0:1:0][0:1:2320][0:1:3200]
and want it so that in the ascii case it goes to THREDDS and in
the kml case it goes to Pydap.
Ideas we had:
1. Monkey with the appropriate section in the THREDDS java to
redirect when it recognizes the new service type, much as it does with
WCS services. Downside is we would have to monkey with every
revision and could mess up things in unexpected ways in the
process.
2. At the apache or tomcat level, have the redirection made
(is this possible?) based on file type.
3. Some other solution?
A question I pose to Roberto (as he is copied) but may be of
general interest is if there is a way for Pydap to serve OPeNDAP
served data that is at another URL (even if on the same
machine), much as THREDDS can. It is this that would simplify what it
would take for us to use the aggregation capabilities in THREDDS with
Pydap in our own internal scripts as we can still views these as one
file - or does anyone else have general suggestions as how we might
combine the desirable features of each.
-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: address@hidden (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."