[postgis-devel] Re: [postgis-users] GIST index speed

[Markus Schaber]

Hi, Martin,

Martin Davis <mbdavis at refractions.net> wrote:

> Yes, GEOS has CoordinateSequences, and in fact these were introduced 
> first in GEOS to allow exactly this option.  I assumed that this was 
> already being done - someone correct this if it's wrong.
> 
> The PreparedGeometry concept is in GEOS as well.  It is another, 
> possibly more important use for caching.  It caches a lot of data 
> structures, which provides a major speedup for spatial predicates.

We have one usecase where we cut geometries into tiles by JOINing a
table containing the tiles against the table containing the object
geometries, and using intersection(tilegeom, objectgeom).

I think that being able to use PreparedGeometries in this case could
give an enormeous speedup, as some larger geometries cover hundreds of
tiles.

The other idea we had was a set returning function implemented in C,
directly working on GEOS, which knows the tile construction rule and
spits out the geometry fragments, but that was to much effort for now.

Regards,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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