Re: Combining THREDDS and Pydap services

Roy,

At Gallagher's urging I will offer the following suggestions:

What you want to do should be fairly easy to accomplish with Apache  
using the rewrite and proxy modules (mod_rewrite and mod_proxy).

You would need to do some careful reading about how mod_rewrite can  
be used, but from my recent experiments with it I know you can do  
this thing. I am pretty sure that you would be using a reverse proxy  
to achieve your desired result. According to the Apache documentation  
this should be a safe and secure solution (as long as you disable  
forward proxies).

I cannot speak to any performance issues you may encounter with this  
method.


Nathan



On Nov 27, 2006, at 5:43 PM, Roy Mendelssohn wrote:

> 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."

========================================================
Nathan Potter                        The OPeNDAP Project
address@hidden                       http://opendap.org
541.752.1852 voice



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