Re: [netcdf-java] Reading contiguous data in NetCDF files

• To: netcdf-java@xxxxxxxxxxxxxxxx
• Subject: Re: [netcdf-java] Reading contiguous data in NetCDF files
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Wed, 14 Jul 2010 17:25:58 -0600

Hi Jon:

On 7/14/2010 2:51 PM, Jon Blower wrote:

Hi,

I don't know anything about how data in NetCDF files are organized, but
intuitively, I would think that, for a general 2D array, the data at
points [j,i] and [j,i+1] would be contiguous on disk.  Is this right?
(i is the fastest-varying dimension)

yes, for variables in netcdf-3 files

I might also suppose that, for an array of size [nj,ni], that the data
at points [j,ni-1] and [j+1,0] would also be contiguous.  Is this true?

yes, for variables in netcdf-3 files that dont use the unlimited dimension

If so, is there a method in Java-NetCDF that would allow me to read
these two points (and only these two points) in a single operation?

(Background: I'm trying to improve the performance of ncWMS by
optimising how data is read from disk.  This seems to involve striking a
balance between the number of individual read operations and the size of
each read operation.)

Thanks,
Jon

--
Dr Jon Blower
Technical Director, Reading e-Science Centre
Environmental Systems Science Centre
University of Reading
Harry Pitt Building, 3 Earley Gate
Reading RG6 6AL. UK
Tel: +44 (0)118 378 5213
Fax: +44 (0)118 378 6413
j.d.blower@xxxxxxxxxxxxx
http://www.nerc-essc.ac.uk/People/Staff/Blower_J.htm


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