[gdal-dev] Spatial index to raster VRT

[Even Rouault]

On Thursday 26 May 2016 13:26:38 Jukka Rahkonen wrote:
> 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.

Actually, this is not true (although I might have in the past say so). The doc 
currently states :
"""
Overview: This optional element describes one overview level for the band. It 
should have a child SourceFilename and SourceBand element. The SourceFilename 
may have a relativeToVRT boolean attribute. Multiple elements may be used to 
describe multiple overviews. 
"""

and I've verified it works (at least they are reported by gdalinfo)

Even

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