[geos-devel] question about GEOSUnion?

[Mateusz Loskot]

LiN YongHeng wrote:
> Hello everyone, I have a question about GEOSUnion(). I give value to 
> g1 and g2 like below: GEOSGeom g1 = "POLYGON ((1  3, 1  3, 1  6, 1 6,
> 1 3))"  and GEOSGeom g2 = "POLYGON ((1  3, 1  3, 1  6, 1  6, 1 3))"
> , but if I make union operation like GEOSGeom g3 = GEOSUnion(g1, g2),
> it give me result like "GEOMETRYCOLLECTION EMPTY". Does anyone can
> tell me why?

LiN YongHeng,

In order to be able to use GEOS or PostGIS, you need to read and
understand some basic informations included in the OGC Simple Feature
Specification

http://www.opengeospatial.org/standards/sfs

Otherwise, you will be hit the wall when you try to use every function.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org