[gdal-dev] gdal_calc.py floating point arithmetic

Andrew C Aitchison andrew at aitchison.me.uk
Thu Jul 14 23:12:42 PDT 2016

On Fri, 15 Jul 2016, Sam Wilson wrote:

> Hi,
> I’m attempting to linearly interpolate two geotiff files using gdal_calc.py.  The geotiff files are 3 hours apart, so for example hour 0 and hour 3.  I’d like to end up with hourly data, so I need hours 1 and 2.
> Below are the commands I’m using:
> However, hour1.tif and hour2.tif appear to be the exact same.
> Does gdal_calc.py not allow using floating point values in the calculation?

I don't know but imagine that there is a scaling either in the 
generation, the comparison or the diplay.

> Or, am I doing something else wrong?

Yes. You ned something like:
  gdal_calc.py -A hour0.tif -B hour3.tif —outfile=hour1.tif —calc=“(A*0.667)+(B*0.333)”
  gdal_calc.py -A hour0.tif -B hour3.tif —outfile=hour2.tif —calc=“(A*0.333)+(B*0.667)”

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