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Add hack to deal with DAP2 signed byte conversion. #1317

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merged 1 commit into from
Feb 13, 2019
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Commits on Feb 13, 2019

  1. Add hack to deal with DAP2 signed byte hack.

    re: issue #1316
    
    The DAP2 data model does not have a signed byte type,
    but netcdf-3 does have (only) a signed byte type.
    So, when converting a netcdf-3 signed byte typed variable to
    a DAP2 unsigned byte, the following actions are taken by thredds:
    1. The variable type is marked as DAP2 (unsigned) byte.
    2. A special attribute, "_Unsigned=false" is set for the variable
    3. The corresponding "_FillValue" attribute, if any, is up-converted
       to the DAP2 Int16 type in order to hold, with sign, any signed byte
       fill value.
    
    On the netcdf-c side, this looks like a fillvalue type mismatch and causes
    an error. Instead, the netcdf-c dap2 conversion code needs to recognize
    this hack and undo it locally.
    
    So this change looks for the above case, and if found, then it properly
    converts the _FillValue type to netcdf-3 signed byte.
    
    Since DAP2 supports both signed and unsigned integers of sizes 16 and 32 bits,
    this should be the only hack needed (famous last words).
    
    It may later be desirable for the thredds DAP2 converter to modify its
    behavior as well.
    DennisHeimbigner committed Feb 13, 2019
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