[gdal-dev] gdal_translate truncates nodata_value < -4.21358e-09

[Siebe Bosch]

Dear list,

I am trying to convert one band from a GRIB2-file into an ASCII raster, 
using gdal_translate.
Upon inspection (opening the original raster using the MapWinGis 
ActiveX-component) and requesting the nodata_value, I get this:

? mygrid.Header.NodataValue
-3.40282346638529E+38 {Double}
     Double: -3.40282346638529E+38 {Double}

So far, so good. Now l tried to convert to ASCII using gdal_translate, 
with the arguments "-of AAIGrid -b 13" (to ASC, band #13)
Much to my surprise the nodata-value (inside the grid) has changed in 
-4.2135788191899337e-009. A NODATA_value in the header has not been set 
at all!

So I tried converting to an ERDAS IMG file. Arguments: "-of HFA -b 13"
Inspecting the results in QGIS I see in the metadata that the 
"nodata-value has not been set". The grid itself however contains data 
of the Float type, and the cells that should have nodata-values have now 
values of -4.21358e-09

My conclusion:

GDAL_Translate does not support numbers smaller than -4.21358e-09. Am I 
right?

The problem however is that I do need the nodata-cells to be recognized 
correctly. Is there any tool that can help me to correct this? E.g. can 
I change the nodata-value of the original (multi-band) grid on forehand? 
Or are there additional arguments for gdal_translate that allow values 
up to the original nodata_value?

Many thanks,
Siebe











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