[Gdal-dev] GDAL vs ArcGIS raster calculator

[Matt Wilkie]

Frank wrote:
>> Note, this script does not set the nodata value.  That could be
>> done as an additional step with gdal_translate, or is left as an
>> exercise for the reader. :-)

To set a nodata value without creating a new raster, see this modest
script, gdalsetnull.py:
http://code.google.com/p/maphew/source/browse/trunk/gis/gdal_extras/bin/gdalsetnull.py

cheers,

matt wilkie
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joosthoek wrote:
> Hi Frank,
> 
> Thanks for your reply, I'll try it out using python. Yeay, nodata
> worked using gdal_translate -nodata 0. One other question, is it also
> possible to use not python but .NET?
> 
> Cheers,
> 
> Jelmer
> 
> 
> Frank Warmerdam-2 wrote:
>> Jelmer,
>> 
>> The calculation appears to be correcting for 16 bit signed integer
>> data that was incorrectly treated as unsigned.  It also marks
>> post-adjusted values of -32768 as nodata.
>> 
>> You should be able to do something similar with a numpy python
>> script like the following (which works with FWTools):
>> 
>> #!/usr/bin/env python
>> 
>> import gdal import gdalnumeric
>> 
>> x = gdalnumeric.LoadFile('utm.tif')
>> 
>> x_adjusted = gdalnumeric.choose( \ gdalnumeric.greater( x, 32767 ),
>> (x, x-65536) )
>> 
>> x_adjusted = x_adjusted.astype(gdalnumeric.Int16)
>> 
>> prototype_ds = gdal.Open( 'utm.tif' ) gdalnumeric.SaveArray(
>> x_adjusted, 'utm2.tif', prototype = prototype_ds )
>> 
>> 

>> 
>