[gdal-dev] Overview resampling generating non-existant values

[thomas bonfort]

For COG format, you should use -co RESAMPLING=mode. gdalwarp's -r switch
only applies to the full resolution warper resampling, not the overviews.
TB

Le mer. 21 août 2024, 18:09, Justin Terry via gdal-dev <
gdal-dev at lists.osgeo.org> a écrit :

> Hi,
>
>
>
> I'm experiencing a strange issue I've never seen before where certain
> resampling methods that should only include values in the original dataset,
> like mode and nearest, are adding new values in the overviews.
>
>
>
> For example, the original raster contains the following values:
>
>
>
> [0,  1,  2,  4,  5,  8,  9, 10, 16, 17, 18, 20, 21, 32, 33, 34, 36, 37,
> 40, 41, 42, 64, 65, 66, 68, 69, 72, 73, 74, 80, 81, 82, 84, 85]
>
>
>
> I resample it using the following command:
>
>
>
> gdalwarp dataset.tif dataset_cog.tif -of COG -co COMPRESS=LZW -r mode
>
>
>
> And when I look at overviews, I start these values, especially as it
> downsamples further:
>
> [ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17,
> 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
> 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55,
> 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74,
> 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 90, 91]
>
> I saw the same if I tried it with nearest resampling. Maybe I'm
> misunderstanding, but I would think these resampling methods would retain
> the original values, and not interpolate any in-between values.
>
> I'm using GDAL version 3.9.1 on Mac M3 from Homebrew.
>
> Thanks,
> Justin
>
>
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