Clean internal overviews but file size not change

[ningfc]

What is the bug?

File size not change after remove internal overviews with command gdaladdo -clean filename.tif

Steps to reproduce the issue

1. Run gdaladdo -clean filename.tif from command
2. Check file size , not change.
3. Then run gdaladdo filename.tif
4. Check file size , increased
5. Repeat 1-4, file size will increase every time, but not decrease.

Versions and provenance

v3.8.3

Additional context

No response

[jratike80]

You probably did not see this part of the documentation https://gdal.org/programs/gdaladdo.html

For internal GeoTIFF overviews (or external overviews in GeoTIFF format), note that -clean does not shrink the file. A later run of gdaladdo with overview levels will cause the file to be expanded, rather than reusing the space of the previously deleted overviews. If you just want to change the resampling method on a file that already has overviews computed, you don't need to clean the existing overviews.

[ningfc]

Oh, thanks. I got it. But do you feel it's weird?
I think, Allowing to shrink the file size is better. So I guess gdaladdo doesn't shrink file size, maybe had considered it for some reason. I have an idea, we can add a new command config like -purge to shrink file size.
Now if I want to shrink the file size, I use gdal_translate to export a new file. but it takes expend long time if the file is large.

[tbonfort]

if your geotiff is tiled, you should be able to use github.com/airbusgeo/cogger for a very fast rewrite reclaiming space. (the output will be a cog, but a geotiff also nonetheless)

[jratike80]

Oh, thanks. I got it. But do you feel it's weird?

I guess that gdaladdo -purge would be as slow as gdal_translate because it would also need to rewrite all the data. As far as I know "clean" just updates the offsets of the image file directories of the overviews.
If you need to remove overviews frequently for example when testing resampling methods, use external overviews.

[tbonfort]

I have opened airbusgeo/cogger#13 in order to further support geotiff cleaning with cogger. If you have any other ideas you can add them over there.