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I'm using gdal_translate to downsample some data using averaging. The input data uses an Int data type, and I want to store the float values of the pixel averaging.

However, even when I force gdal_translate to use Float32, the values in the output file have been cast to int. The command I'm using is:

gdal_translate -tr 0.0075 0.0075 -r average -ot Float32 -co COMPRESS=LZW -q in.tif out.tif

When I use the same options for gdalwarp, I get the expected result (float values).

gdalwarp -tr 0.0075 0.0075 -r average -ot Float32 -co COMPRESS=LZW -q in.tif out.tif

Am I missing something, or is this a bug in gdal_translate?

  • I believe the same thing applies with gdal_calc.py, where you need to convert image to float explicitly (in expression, e.g. --calc="A.astype(float)"). Since it calculates expression first and only after that converts resulting image into -ot type – dr_times Jul 7 '17 at 12:43
  • The order of the options does not make a difference (nor should it!) @dr_times Yes, I've encountered that with gdal_calc.py; I wondered if it might be a similar issue. However there's no similar ability to force casting for gdal_translate. – BiscuitOverflowError Jul 7 '17 at 13:27
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I understand this is a bit hard to understand, but this is an expected result given the design of both utilities. In gdal_translate, the resampling is done with the input datatype (so Int), the conversion to the output data type is done late in the process. In gdalwarp, -ot Float32 implies a -wt Float32 (working datatype), hence more expected results.

  • Yes, I noticed the -wt option for gdalwarp. AFAICT there's no equivalent option for gdal_translate - correct? – BiscuitOverflowError Jul 10 '17 at 9:36

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