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PODetermining signed state for HDF5 variables in NetCDF
 

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    <p>My team has been given HDF5 files to read. They contain structured data with unsigned variables. I and my team were overjoyed to find the NetCDF library, which allows pure-Java reading of HDF5 files, albeit using the NetCDF data model.</p> <p>No problem---we thought we'd just translate from the NetCDF data model to whatever model we wanted. As long as we get the data out. Then we tried to read an unsigned 32-bit integer from the HDF5 file. We can load up HDFView 2.9 and see that the variable is an unsigned 32-bit integer. But... it turns out that <a href="http://www.unidata.ucar.edu/software/netcdf/docs/BestPractices.html#Unsigned%20Data" rel="nofollow">NetCDF-3 doesn't support unsigned values</a>!</p> <p>To add insult to injury, NetCDF-3 recommends that you "widen the data type" or use an <code>_Unsigned = "true"</code> attribute (I am not making this up) to indicate that the 32 bits should be treated as an unsigned value.</p> <p>Well, maybe those kludges would be effective if I were creating NetCDF data from scratch, but <strong>how can I detect using NetCDF that a 32-bit value in an existing HDF5 file should be interpreted as unsigned?</strong></p> <p><em>Update:</em> Apparently <a href="http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-c/NetCDF_002d4-Atomic-Types.html" rel="nofollow">NetCDF-4 does support unsigned data types</a>. So this begs the question: <strong>How can I determine whether a value is signed or unsigned from the NetCDF Java library?"</strong> I don't see any unsigned types in <code>ucar.ma2.DataType</code>.</p>
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    1. USGarret Wilson
    1. USGarret Wilson
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    1. COWhat about one of the other pieces of software listed on the HDF Group website? http://www.hdfgroup.org/products/hdf5_tools/
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      1. USRobert Harvey
    2. CO@RobertHarvey, I don't see any other pure-Java libraries at that page. And thanks for the link, but even if they did my question would still remain unanswered.
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