[gdal-dev] Spatial index to raster VRT

[Jukka Rahkonen]

Daniel Morissette <dmorissette <at> mapgears.com> writes:

> 
> On 2016-05-26 8:40 AM, Jukka Rahkonen wrote:
> > Hi,
> >
> > Any thoughts about alternatives to implement the feature request from
> > https://trac.osgeo.org/gdal/ticket/5762?
> >
> > What I dream of is to be able to utilize all the nice on-the-fly tweaks that
> > can be done with VRT at similar speed that Mapserver is reaching with
tileindex.
> >
> 
> That would be a nice enhancement. As usual I guess we need a champion 
> and/or some funding to make this happen.
> 
> I came across a similar use case not long ago and realized that to get 
> top performance at all zoom levels we'd also need the ability to 
> associate overviews with the VRT. I didn't check if creating external 
> overviews with gdaladdo would work for a VRT already. Maybe it does?

It does and is even documented in
http://www.gdal.org/gdal_vrttut.html#gdal_vrttut_overviews.

VRT supports one overview, but that can itself be a VRT, which in turn can
point to next VRT overview and so on. Easier than to explain is to give a
link to this old experiment
http://latuviitta.org/documents/GDAL_Scale_dependent_VRT_test.zip

Unzip and open the best resolution VRT t0320.vrt with QGIS, zoom in, and you
should see how 5 different tiff files with different pixel size and
rendering styles behave.

-Jukka Rahkonen-