[Gdal-dev] Another Question about OGRDataSource::ExecuteSQL

[Frank Warmerdam]

jody at ifi.unizh.ch wrote:
> Yeah, this definitely answers my question. But also managed to spark my
> interest with respect to spatial filtering:
> 
> Is the spatial filtering done by brute force, i.e. comparing the
> Extents of every feature with the given OGRGeometry?
> Or is a sort of index created in which the features' extents
> are related with an appropriate encoding with respect to a Quad-Tree, for
> instance?

Jody,

In general the spatial query is applied in a driver determined fashion.
Drivers such as PostGIS and MapInfo TAB which have inherent spatial indexing
already available take advantage of it.  The vast majority of drivers just
read all features and then discard those outside the spatial query area
(including ESRI Shapefiles).

I try to include some notation in the format driver page if a driver has
accelerated spatial indexing.  However, I am not too careful about that.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent