Hi,
I am using geoserver v2.12.2 with the JVM system property to have geoserver unpack NetCDF data with respect to the scale_factor/add_offset attributes: -Dorg.geotools.coverage.io.netcdf.enhance.ScaleMissing=true Geoserver seems to be doing the unpacking fine, but when I configure my coverage.xml to re-pack the data into a smaller datatype (such as byte) the formula used treats the datatype as unsigned and when the NetCDF file is read by external software the values are interpreted incorrectly since NetCDF convention defines the packed data types (Byte, Short, Int) as signed integers. Given this convention, I am curious if there is a reason this algorithm was selected that I'm overlooking or if this is a bug in the software. I would recommend that the formula be updated to use the "signed" one below until "ubyte, ushort, and uint" data types are supported by geoserver for packing. For reference, the formulas are defined in DataPacking.java https://github.com/geoserver/geoserver/blob/master/src/extension/netcdf-out/src/main/java/org/geoserver/web/netcdf/DataPacking.java There is more information at the link below, but these seem to be the two recommended options for data packing while reserving space for missing data. The first is for signed packed values and the second is for unsigned packed values which is the one that geoserver is using. https://www.unidata.ucar.edu/software/netcdf/docs/BestPractices.html#Packed%20Data%20Values In either the signed or unsigned case, an alternate formula may be used for the add_offset and scale_factor packing parameters that reserves a packed value for a special value, such as an indicator of missing data. For example, to reserve the minimum packed value (-2^n\ -\ 1^) for use as a special value in the case of signed packed values: > scale_factor =(dataMax - dataMin) / (2^n^ - 2) > add_offset = (dataMax + dataMin) / 2 If the packed values are unsigned, then the analogous formula that reserves 0 as the packed form of a special value would be: > scale_factor =(dataMax - dataMin) / (2^n^ - 2) > add_offset = dataMin - scale_factor Thanks for any help or information I might be overlooking! - Mrc0113 -- Sent from: http://osgeo-org.1560.x6.nabble.com/GeoServer-Dev-f3819232.html ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Geoserver-devel mailing list Geoserver-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/geoserver-devel
