nodata for writter function in auxil.py

[gr4n0t4]

Hi, the "noData" value for the write function is set to '0'
For ERS1/2 & ASAR sensor it would work best with 'NaN' instead of '0', I'm being told that could be an issue for the "log scaled images" in S1
So to implement this option would it be best to add a optional parameter to the writer function or to check the sensor inside as it is done for writing the SAFE file?
Thank you

[johntruckenbrodt]

Hi @gr4n0t4. True, this value is hard-coded for pyroSAR.snap.auxil.writer. To optionally change the output nodata value would make sense. However, the internally used gdal.TranslateOptions just has a noData parameter which applies to both source and target. Thus, modifying it would omit the source nodata value of 0, which is SNAP's standard. The thing is, SNAP does not write the nodata value in the ENVI HDR files (which are used by both SNAP's BEAM-DIMAP and ENVI output format) so it cannot be read in GDAL when modifying noData (perhaps GDAL assumes 0 if ot cannot read a value though, not quite sure). Easy modifcation of the HDR file to add the nodata value is possible with spatialist.envi:

from spatialist.envi import HDRobject
with HDRobject(hdrfile) as hdr:
    hdr.data_ignore_value = 0
    hdr.write(hdrfile)

Once this is done, passing NaN to gdal.Translate should work fine.

FYI, I have recently restructured the S1_NRB processor to no longer make use of pyroSAR.snap.util.geocode. See S1_NRB.snap.

[gr4n0t4]

Thanks for your reply. We will investigate your solutions