reading raw (packed) data from NetCDF files and avoiding missing-value check

[John Caron]

Hi Jon:

One obvious thing would be to open it as a NetcdfFile, not a GridDataset. Is that a possibility?

Jon Blower wrote:
> Hi,
> 
> I'm writing an application that reads data from NetCDF files and
> produces images.  I've noticed (through profiling) that a slow point
> in the data reading process is the unpacking of packed data (i.e.
> applying scale and offset) and checking for missing values.  I would
> like to minimize the use of these calls.
> 
> To cut a long post short, I would like to find a low-level function
> that allows me to read the packed data, exactly as they appear in the
> file.  I can then "manually" apply the unpacking and missing-value
> checks only to those data points that I need to display.
> 
> I'm using nj22, version 2.2.16.  I've tried reading data from
> GeoGrid.subset() but this (of course) performs the unpacking.  I then
> tried getting the "unenhanced" variable object through
> GeoGrid.getVariable().getOriginalVariable(), but (unexpectedly) this
> also seems to perform unpacking and missing-value checks - I expected
> it to give raw data.
> 
> Can anyone help me to find a function for reading raw (packed) data
> without performing missing-value checks?
> 
> Thanks in advance,
> Jon
> 

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