Hi.
First of all, sorry if that's not a java specific topic.
I'm working on supporting dataPacking when storing a dataset to a NetCDF
output file. Suppose I have Double data in the range [-10 : 35] (as an
instance, a temperature in celsius degrees) where the input _fillValue is
-65536.
I want to write it as packed data (as an instance, Byte... it's just an
example).
I'm using the formula provided here
<https://www.unidata.ucar.edu/software/netcdf/workshops/2010/bestpractices/Packing.html>
.
Therefore, I'm computing dataMin, dataMax: -10, 35 in my case (-65536 is
not part of the statistics computations).
Then, I'm using them to compute add_offset and scale_factor:
add_offset = dataMin
scale_factor = (dataMax - dataMin) / (2^n - 1)
I'm setting out a NetCDF Variable with short dataType and I'm rescaling the
values on the fly using that formula:
packed_value = nint((unpacked_value - add_offset) / scale_factor)
Note that I'm avoiding to apply this transformation to samples with value =
-65536 (being my NoData, _fillValue).
The question is:
I want to setup a _fillValue in the packed dataset.
It need to respect the output dataType (so, it's a Byte).
_fillValue = -65536 won't fit in the Byte range. What is the recommended
approach to compute the "output" _fillValue?
Moreover, what can I do to make sure that I still have a "reserved" value
in the output range, to be used to represent _fillValue without risking
overlaps with the converted range?
Should I use some additional "offsets" when computing the
add_offset/scale_factor to make sure as an instance, that the first value
of dataType range is reserved for _fillValue? (as an instance, to make sure
that _fillValue = 0 and valid range will be between 1 and 255)
Please, let me know.
Best Regards,
Daniele
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