[gdal-dev] Downsample with averaging?
Jennings.Jay at geoeye.com
Mon Feb 21 15:26:44 EST 2011
(using GDAL 1.8.0) I am trying to create a 32:1 down-sampled overview of a GeoTiff satellite image. My first thought was gdal_translate, with args such as "-outsize 3.125% 3.125%"... which produces surprisingly high quality given the absence of a resampling option. However I'm looking for a downsampling scheme that creates a result pixel by averaging all relevant source pixels (I know, for 32:1 downsample, that means 1024 source pixels for each result pixel !) with the hope of an output that is not "speckled" or "grainy" insofar as possible.
I also looked at gdaladdo, which does have the "-r average" resampling option... the guidance at gdal.org seems to suggest that it can produce a 32:1 GeoTIFF external overview with a command like this:
gdaladdo -r average -ro XXXXX.tif 32
But that produces a surprising error message, namely:
ERROR 4: `XXXXX.tif.ovr' does not exist in the file system, and is not recognised as a supported dataset name.
Am I barking up the wrong tree with gdaladdo for this purpose ? Anybody have any suggestions for highest-quality down-sampling ? Thanks in advance.
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