[gdal-dev] Indexing lots of remote COGs for use with gdal raster clip and QGIS

[Even Rouault]

Le 01/09/2026 à 15:33, Robin Wilson via gdal-dev a écrit :
> Hi,
>
> I have a lot of COGs hosted online in HTTP RANGE compatible storage. I 
> want to create a catalog/index of them so that GDAL and tools that use 
> GDAL (like QGIS) can extract the relevant data from the COGs for 
> specific areas. For example, I’d like to use `gdal raster clip` to 
> clip this big ‘virtual raster’ to a specific bbox or polygon. Ideally 
> I’d also like to be able to view the big raster on-the-fly in QGIS, 
> but I’m aware that may be more difficult. My tiles are ’true tiles’ in 
> that they tessellate properly and each location is in a single file.
>
> I’ve been looking at the GDAL Tile Index format, but have been getting 
> a bit confused, and some things haven’t been working quite how I 
> expect. A few questions below:
>
> 1. Is there an easy way to generate a GDAL Tile Index file from a file 
> containing a list of remote URLs? I couldn’t find the right way to 
> specify a file containing URLs on the command line, so I ended up 
> writing a short Python script that loads the list of URLs from a file 
> and then passes them to gdal.TileIndex. Is that the best way to do 
> this? One disadvantage of this method is that I can’t seem to get a 
> progress bar to display.

see 
https://github.com/OSGeo/gdal/blob/master/autotest/utilities/test_gdalalg_driver_gti_create.py 
. The input argument can be a list of paths, local or remote (/vsis3/ etc)

you can use gdal.alg.vsi.list to get a list of remove /vsis3/ files

>
> 2. My current way of doing that requires GDAL loading the bbox of each 
> file by requesting it over the network, which is fairly slow, and I 
> have thousands of files to do this for. Is there a way to get the GTI 
> creation to use local files on my hard disk for getting the extent of 
> each file, but save the location as a /vsicurl/ URL to the remote file?
Not directly, but if you save in a .gpkg your GTI index, you can easily 
patch the 'location' field from local paths to remote URLs
>
> 3. Once I’ve created the file, I can do `gdal raster clip` operations 
> on the command-line quite quickly, but if I load the GTI raster into 
> QGIS then QGIS just hangs. I hoped it would just request the relevant 
> COGs for the area I was looking at. I’ve tried loading it in by 
> dragging and dropping the .gti.gpkg file and then selecting the raster 
> in the layers popup, and also adding it via Add Layer->Raster and 
> putting ‘GTI:<path>’. I have a web map working which loads these COG 
> files on the fly depending on where you’re looking (using a minimal 
> STAC catalog in a JSON file) and was hoping to have the same thing 
> working in QGIS, without the effort of setting up something like 
> titiler or titiler-pgstac, as I’m currently managing to get away 
> without running any servers  (as opposed to static data stores) for 
> this data.

QGIS will try to gather statistics, hence this can be slow. One way to 
speed up is to have overviews defined in the GTI.


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