Re: [thredds] Grid Map versus root variable

I have converted this to a unidata bug report.
See https://www.unidata.ucar.edu/jira/browse/CDM-68

=Dennis Heimbigner

John Caron wrote:
Hi Roy, Roberto:

Yes, we see the problem and will get a fix for it, thanks!

John

On 11/27/2011 8:13 PM, Roy Mendelssohn wrote:
Hi All:

This came up in the pydap  mail list.  I am quoting Roberto here:

Sorry, but the fact that it works with some clients doesn't mean it's working as intended. In that dataset there are two different ways to retrieve the time axis:

(1) http://thredds1.pfeg.noaa.gov/thredds/dodsC/satellite/GR/ssta/1day.dds?analysed_sst.time (2) http://thredds1.pfeg.noaa.gov/thredds/dodsC/satellite/GR/ssta/1day.dds?time

If you check the DDS responses above, you'll see that the two are identical. This is because "time" is a map in the "analysed_sst" grid, but also a variable in the root dataset, as we can see from the unconstrained DDS:

http://thredds1.pfeg.noaa.gov/thredds/dodsC/satellite/GR/ssta/1day.dds

Now, if you replace the ".dds" extension in the two requests above with ".dods", you'll notice that the first one returns a "Request Too Big" error, while the second one is fine. My guess is that there's a bug in the code that estimates the size of the requests.

Why does this work with other clients? As far as I know, pydap is the only opendap client that does requests for the grid map (request #1 above), instead of requests for the root variable (#2). Other clients that I've seen prefer the second approach. I use the first one because... well, guess because I'm a purist who sometimes favors purism over practicality*. :-P

I can confirm what he reports here (it actually started with an email from Chris Mueller who was getting the reported "Request too big" error on some datasets even though he was making small requests using the pydap client code. If you use the html page or ERDDAP or toolsUI it works, but it fails with pydap for the reason given. I believe Roberto is correct here that you should be able to query the grid map, which means there is an error of some sort.

-Roy



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"The contents of this message do not reflect any position of the U.S. Government or NOAA."
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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@xxxxxxxx (Note new e-mail address)
voice: (831)-648-9029
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"the arc of the moral universe is long, but it bends toward justice" -MLK Jr.

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