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I want to have mutiple overview files (one for each overview level) for a GeoTiff, so I'm able to edit this files in a raster editor. How can this be done?

Unfortunately, gdaladdo -ro creates only one .ovr file for a tiff, that contains all the overviews.

Maybe this can be done by using VRT format and specifying particular tiff files as overviews for a main one?

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It looks that this has been asked in the gdal-dev mailing list some years ago http://osgeo-org.1560.x6.nabble.com/gdal-dev-Scale-dependent-VRT-for-overviews-td4966814.html

You were right with your thinking about using the VRT format.

You can define one and only one source for externals overviews in VRT. However, it is possible to use a trick and point the first level VRT to read overviews from a second level VRT file which is defined to read its own overviews from a third level overviews and so on.

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Another option would be to create just a level 2 overview, then a level 2 overview for that, then a level 2 overview for that and so on. You will get file.tif.ovr.ovr.ovr.ovr and so on. So instead of having a level 4 overview for the original image, you have a level 2 overview for its level 2 overview.

At least GDAL (and thus QGIS) supports that just fine.

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