On Fri, 31 Jul 2020, Federico Gianoli wrote:
Thanks Even,
If I look at the metadata of my netcdf, the values of "offset" and "scale
factor" are in float64 instead of float32. So the correct values to read
should be -0.08 as offset and 0.004 as scale factor.
If I open the netcdf in SNAP, for example, I am able to correctly see this
information. So, I suppose that, by default, gdal reads metadata values in
float64 instead of 32bit, and I would like to know if there is a way to
force gdal to read these values as float32.
NC_GLOBAL#title=10-daily Normalized Difference Vegetation Index 333M:
GLOBE 2020-06-21T00:00:00Z
NDVI#add_offset=-0.079999998
NDVI#flag_meanings=Missing cloud snow sea background
NDVI#flag_values={251,252,253,254,255}
NDVI#grid_mapping=crs
NDVI#missing_value=255
NDVI#scale_factor=0.0040000002
NDVI#valid_range={0,250}
NDVI#_FillValue=255
Does SNAP allow you to display the values with more precision ?
If they were exactly -0.08 and 0.004 before conversion to Float64
the values actually stored will be more like -0.08000000000000000167
and 0.00400000000000000008 (printed in C with "%.20lf")
Could the initial data have been Float32, converted to Float64
to be stored in the netcdf ?
I guess what you really want is for gdal to read in Float64 data and
convert it to Float32 for processing/outout ?
Evan's suggestion of "-ot Flat32" will give you 32bit output.
No. What do you mean by "The Netcdf data type is declared in the metadata
as "Float"" ? Is this some text attribute that would override the native
data type, which would be Float64 ? the GDAL netCDF driver has proper
support for both Float32 or Float64 based on the data types of variable.
If you need to override it, your best option is to use the -ot Float32
switch of gdal_translate to down cast.
--
Andrew C. Aitchison Kendal, UK
[email protected]
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