Cut hillshade under certain treshold to make near to flat land transparent

[yohanboniface]

Need is to avoid the flat lands becoming grey (here only part of the data has hillshade, and so we see the colour changing):

[yohanboniface]

Example from the doc of gdal_calc.py (thanks to @AndrewBuck):

# gdal_calc.py -A input.tif --outfile=result.tif --calc="A*(A>0)" --NoDataValue=0

[yohanboniface]

See also: https://gist.github.com/cquest/8179870

[yohanboniface]

Fixed, thanks a lot @cquest for the recipe!