[postgis-users] ST_intersection

[Graham Glanfield]

Dear list,

The following query:

SELECT ST_intersection(st_geometryfromtext(('MULTIPOLYGON(((-3.577895 
53.954289,0.816178 54.779474,2.624587 51.01611,0.702327 
50.669834,-1.425339 50.243136,-1.424992 50.243209,-3.577895 
53.954289)))'),4326)::geography,st_geometryfromtext(('POLYGON((-0.38928 
51.5446,-0.1703 51.5446,-0.1703 51.389328,-0.38928 51.389328,-0.38928 
51.5446))'),4326)::geography);

fails with the following error:
"ERROR:  Error performing intersection: TopologyException: Input geom 0 
is invalid: Self-intersection at or near point 1482705.9601906976 
781580.61046449794 at 1482705.9601906976 781580.61046449794"

If I remove "::geography" from both geometry's, it works. It also works 
if I add a small buffer to the first geometry. Postgis reports that both 
geometry's are valid.

I'm running:

PostgreSQL 9.4.1 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 
4.8.2 20140120 (Red Hat 4.8.2-16), 64-bit POSTGIS="2.1.5 r13152" GEOS
="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 
1.11.2, released 2015/02/10" LIBXML="2.9.1" LIBJSON="UNKNOWN" TOPOLOG
Y RASTER

Any help appreciated.

Regards,
Graham

-- 
Graham Glanfield
Geocento Ltd
Electron Building
Fermi Avenue
Harwell
Didcot
Oxfordshire
OX11 0QR

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