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yes, bob is correct. use opendap for remote access. On 10/11/2012 11:30 AM, Brian Schlining wrote:
Bob's response is below. -- Brian Schlining Forwarded message:*From:* Bob Simons <bob.simons@xxxxxxxx> *To:* Brian Schlining <bschlining@xxxxxxxxx> *Date:* Thursday, October 11, 2012 10:05:47 AM *Subject:* Re: ERDDAP bug I understand the issue that you are talking about. I would instead urge you not to use this approach. This approach has the implicit assumption that there is a static .nc file with the requested subset of the larger dataset and that NetCDF-Java can read specific bytes from that file. See http://www.unidata.ucar.edu/software/netcdf-java/reference/HTTPservice.html That is just not a good way to think about that file. Please request a .nc file from ERDDAP only if you want to download that .nc file. For your purposes, please use NetCDF-Java to access an ERDDAP dataset as an OPeNDAP dataset. This is what OPeNDAP was designed for and NetCDF-Java supports this *very* well. This approach will work *much* better, for a variety of reasons. Here is a code snippet: NetcdfFile ncFile = NetcdfDataset.openFile("http://beach.mbari.org:8180/erddap/griddap/erdRyanSST";, null); //note that there is no file extension at the end of the dataset's name //Then you can do what you want with the ncFile object. I will improve the documentation related to this. Thanks for pointing out this weakness in the documentation. I hope that clarifies the situation. If not, or if you have other questions about ERDDAP, please let me know. P.S. I am not on netcdf-java mailing list. Can you please post this response on the netcdf-java mailing list? Thank you. On 10/11/2012 9:31 AM, Brian Schlining wrote:Hi Bob, We're doing some work with ERDDAP and running into an issue using NetCDF-Java to access files served by ERDDAP. I think I understand the issue and know how to address it, so I'm passing the info onto you all so it can be addressed. So here goes: 1) ERDDAP allows one to download a NetCDF file by building a link appended with '.nc'. The link URL for the netcdf file would be something like http://beach.mbari.org:8180/erddap/griddap/erdRyanSST.nc. This works great for downloading the files. However, it does NOT work with the NetCDF-Java API; NetCDF-Java can normally read NetCDF files from arbitrary non-opendap http urls. 2) The reason it fails is because NetCDF-Java needs to know the size of the file being served. This requires that the HTTP response for a URL like http://beach.mbari.org:8180/erddap/griddap/erdRyanSST.nc to contain a 'Content-Length' field. ERDDAP is not sending that … here's a response header from ERDDAP (notice there's no 'Content-Length': HTTP/1.1 200 OK Server: Apache-Coyote/1.1 Date: Thu, 11 Oct 2012 15:44:19 GMT Last-Modified: Thu, 11 Oct 2012 15:44:19 GMT xdods-server: dods/3.7 erddap-server: 1.38 Content-Disposition: attachment;filename=erdRyanSST_8571_f367_229e.nc Content-Encoding: Content-Type: application/x-download Transfer-Encoding: chunked 3) Since ERDDAP is running on Tomcat, the only way I know of to set the 'Content-Length' is to explicitly call 'response.setBufferSize()' in the servlet that returns the NetCDF file. Note that once the response size goes beyond the bufferSize, Tomcat will fallback to 'Transfer-Encoding: Chunked' (which we don't want). So make sure you're setting the buffer size to the correct value. Hope that helps! p.s. I cc'd this to the netcdf-java mailing list in case I got something wrong. Hopefully someone will correct me. Cheers -- B ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Brian Schlining MBARI Software Engineer, Research and Development brian@xxxxxxxxx <mailto:brian@xxxxxxxxx> (831) 775-1855 http://www.mbari.org/staff/brian-- Sincerely, Bob Simons IT Specialist Environmental Research Division NOAA Southwest Fisheries Science Center 1352 Lighthouse Ave Pacific Grove, CA 93950-2079 Phone: (831)658-3205 Fax: (831)648-8440 Email: bob.simons@xxxxxxxx <mailto:bob.simons@xxxxxxxx> The contents of this message are mine personally and do not necessarily reflect any position of the Government or the National Oceanic and Atmospheric Administration. <>< <>< <>< <>< <>< <>< <>< <>< <><_______________________________________________ netcdf-java mailing list netcdf-java@xxxxxxxxxxxxxxxx For list information or to unsubscribe, visit: http://www.unidata.ucar.edu/mailing_lists/
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