[gdal-dev] Calculate footprints of shapefiles

[Chaitanya kumar CH]

Armin,

Cascaded Union works pretty much like Union except that it is optimized to
work on more than two geometries.
Both OGR and PostGIS uses the GEOS library to perform this.

Read this blog entry by Paul Ramsey:
http://blog.cleverelephant.ca/2009/01/must-faster-unions-in-postgis-14.html

On Wed, Mar 16, 2011 at 3:41 PM, Armin Burger <armin.burger at gmx.net> wrote:

> Chaitanya
>
> thanks for the hints. So a sort of Union operation seems to be necessary. I
> need to check how fast that is with OGR on larger shapefiles (I want to
> store in PostGIS just the footprint, not the full geometry collection). The
> ConvexHull could be a good alternative to a simplified boundary.
>
> I understand how the normal Union() works, it merges 2 geometries into a
> new one. But I don't get it what UnionCascade() is doing. It applies a Union
> on a single geometry and returns the new geometry, what is it actually
> unioning/merging then?
>
> Regards,
> Armin
>
>
> -------- Original-Nachricht --------
> > Datum: Wed, 16 Mar 2011 10:06:57 +0530
> > Von: Chaitanya kumar CH <chaitanya.ch at gmail.com>
> > An: armin.burger at gmx.net
> > CC: Marius Jigmond <mariusjigmond at hotmail.com>, gdal-dev at lists.osgeo.org
> > Betreff: Re: [gdal-dev] Calculate footprints of shapefiles
>
> > Armin,
> >
> > This can be done in either OGR or PostGIS.
> >
> > For OGR, refer to the OGRGeometry class reference, especially the
> > ConvexHull(), Union() and UnionCascaded() functions.
> > For PostGIS, ST_Boundary() and ST_Union().
> >
>
>
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-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
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