[gdal-dev] Adding external overviews for a VRT whose source tiles already have overviews

[Craig de Stigter]

This was my mistake. I had set `GDAL_DISABLE_READDIR_ON_OPEN=EMPTY_DIR`,
which was preventing GDAL from noticing the .vrt.ovr file I had generated.

So, the answer is that the .vrt.ovr is just a TIF file, and it can be
generated via gdal_translate and additional overviews added to it via
gdaladdo 👍

Thanks :)

On Wed, 17 Jul 2024 at 19:59, Craig de Stigter <
craig.destigter at koordinates.com> wrote:

> Hi folks
>
> I have a VRT which is a mosaic of several thousand s3-stored COGs. Doing
> any kind of low-res downsampling from this VRT causes very slow performance
> and high memory usage because it causes requests to all the individual
> source tiles.
>
> I'd like to add external overviews to the VRT via a `.vrt.ovr` file – and
> it appears I can do this with gdaladdo.
>
> However, a naive call to gdaladdo seems to ignore the overviews on all the
> source files, rendering the overviews by downloading every pixel from the
> full-size sources. This is a nonstarter in this environment where the full
> set of source tiles is enormous and remote.
>
> So, two questions:
> 1. Is there a way to force gdaladdo to use the COG overviews from the
> source VRT's source tiles?
> 2. If not, are there any other ways to generate a `.vrt.ovr` file which
> would use the source overviews? I have tried using gdal_translate to
> produce a .tif of the right pixel size and then renaming it to `.vrt.ovr`,
> but it doesn't seem to be used by GDAL – so I guess there's more to `ovr`
> files than just TIF files with the right name!
>
> --
> Regards,
> Craig
>
> Platform Engineer
> Koordinates
>
> +64 21 256 9488 <+64%2021%20256%209488> / koordinates.com / @koordinates
> <https://twitter.com/koordinates>
>


-- 
Regards,
Craig

Platform Engineer
Koordinates

+64 21 256 9488 <+64%2021%20256%209488> / koordinates.com / @koordinates
<https://twitter.com/koordinates>
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