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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Tom Whittaker wrote:
I found there has been some discussion about having a variable attribute "_Unsigned" that would allow for unsigned byte data to be supported. Well, one of our people created a netCDF file with bytes which he treated as "unsigned"....but when he read the file and specified a (float) scale and offset, he got the "wrong" answers...until he started treating the byte values as signed -- his unhappiness is that IDL apparently treats bytes as unsigned, so he cannot easily use his file in both (IDV is the other one) places. I tried a few combinations in the toosUI, using NCML, but could not get anything to work... Is this supported? If so, is there some magic? (I'm running netCDF-java 4.1). Thanks... tom
Hi Tom:Classic netcdf has only signed bytes. netcdf-java introduced the concept of unsigned bytes by adding an attribute
varname:_Unsigned = "true";This only matters to the library when you are doing scale/offset. of course, the application also wants to deal with it when using it in calculations, see:
http://www.unidata.ucar.edu/software/netcdf-java/reference/DataType.html for more info.If IDL insists on treating bytes as unsigned, then storing as unsigned with attribute as above should work in both places. If you have a file where this isnt working in IDV, send it to me and ill check it out.
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