[gdal-dev] GTI: override SRS of source tiles (disable reprojection)

[Scott]

If your rasters are invalid with bad projections or unreadable by 
gdalinfo, disregard the following.

One way to create massive tile index's with individual rasters having 2 
or more different projections is to use good old gdaltileindex. It will 
create an index of tiles (raster files) and bounding box geometry in a 
specified EPSG without altering the underlying raster projection. Such as:

gdaltindex
    -lyr_name bbox
    -tileindex file
    -t_srs EPSG:4326
result.fgb rast_3857.tif rast_4269.tif

The bbox geometry column will be 4326, regardless of what the raster is. 
The above will create a tile index in FlatGeobuf format. FGB is 
important because now you can grab a bbox of only the rasters you need. 
Your client/user will still have to deal with the different projections 
of each raster in the index.

While GTI can also use FGB, gdaltileindex with FGB is a bit more 
lightweight. You can do lots of flexible, non-standard things by adding 
meta data (or whatever) for each tile. Here's a write-up and working 
example using 1 FGB tile index, 514 COG's and a LeafLet client:

https://www.postholer.com/fgbcog/

Hope that helps!
Scott

On 3/18/25 17:13, Craig de Stigter via gdal-dev wrote:
> Hi folks
> 
> I'm working on converting an existing VRT mosaic pipeline to use GTI to 
> improve its scalability with huge layers.
> 
> A problem is that our individual raster tiles may have projections with 
> subtly varying WKT, since they were often produced by customers using 
> different tooling and in different places. The WKT in the tiles may even 
> be altogether incorrect or missing (even though they're actually all the 
> same projection as the GTI file itself).
> 
> With VRT this was not a problem since the VRT file didn't support 
> reprojection and just overrode the projection of its tiles. But with GTI 
> I think the driver is unnecessarily passing everything through the warp 
> kernel.
> 
> Is there a way to override the projection of the source tiles when using 
> the GTI driver?
> 
> -- 
> Regards,
> Craig
> 
> Platform Engineer
> Koordinates
> koordinates.com <http://koordinates.com/> / @koordinates <https:// 
> twitter.com/koordinates>
> 
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