[gdal-dev] Removing default nodata value from netCDF driver ?

[Even Rouault]

Hi,

It has been raised to my attention that the netCDF driver systematically 
reports a nodata value when opening a dataset, even if no explicit _FillValue 
metadata item is set in the product. This seems to be a behaviour that has 
existed forever, but I'm not clear why. For byte/ubyte data types, the nodata 
value is set to 0 by default.

But for some products, like Sentinel 3 S3A_SL_2_LST products, in the 
LST_ancillary_ds.nc file, 0 is a valid value.

See following extract of ncdump on such a product:

        ubyte biome(rows, columns) ;
                biome:flag_meanings = "open_ocean irrigated_cropland 
rainfed_cropland mosaic_cropland mosaic_vegetation 
broadleaved_evergreen_forest closed_broadleaved_deciduous_forrest 
open_broadleaved_deciduous
_forest closed_needleleaved_forest open_needleleaved_forest mixed_forest 
mosaic_forest mosaic_grassland shrubland grassland sparse_vegetation 
freshwater_flooded_forest saltwater_flooded_forest flooded_vegetation 
artificial_surface bare_area_unknown bare_area_orthents bare_area_sand 
bare_area_calcids bare_area_cambids bare_area_orthels water snow_and_ice 
unfilled" ;
                biome:flag_values = 0UB, 1UB, 2UB, 3UB, 4UB, 5UB, 6UB, 7UB, 
8UB, 9UB, 10UB, 11UB, 12UB, 13UB, 14UB, 15UB, 16UB, 17UB, 18UB, 19UB, 20UB, 
21UB, 22UB, 23UB, 24UB, 25UB, 26UB, 27UB, 28UB ;
                biome:long_name = "Gridded GlobCover surface classification 
code" ;

So per https://github.com/OSGeo/gdal/pull/1979, I'm proposing to remove this 
default nodata value. Anybody seeing a side effect to this ?

Even

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