[postgis-users] GeomUnion and Intersection

[roxana at torre.nl]

Hello,
I'm getting something further with my worldmap database. I have the esri
shapefile of Europe in it, now I'm trying to get data and visualize it. I'm
using the gml output, and that's going fine. 
The idea is to get all borders and coastlines, I want to have as less as
possible points. The queries I'm using are like this:

for the coastlines:

SELECT AsGML(simplify(GeomUnion((SELECT the_geom FROM worldmap WHERE cntry_name
='France'),GeomUnion((SELECT the_geom FROM worldmap WHERE cntry_name
='Netherlands'),(SELECT the_geom FROM worldmap WHERE cntry_name
='Belgium'))),0.05));

and for each pair of countries:

SELECT AsGML(simplify(Intersection((SELECT the_geom FROM worldmap WHERE
cntry_name ='France'),(SELECT the_geom FROM worldmap WHERE cntry_name
='Belgium')),0.05));

Is there another way to do this?. Specially for the first query: i saw you can
also use it with "geometry set" but I couldn't find what that is.

Thanks,
roxana

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