Mark Cave-Ayland wrote:
Mike Leahy wrote:Hello list,I'm having a problem with st_difference, where two overlapping geometries will return an empty geometrycollection, as if the do not overlap. However, if I use st_difference on the same geometries, but converted to EWKT, then back, then using st_difference yields the expected output. Basically, this is what I'm getting (minus the output coords):# select st_astext(st_difference(g1,g2)), st_astext(st_difference(st_asewkt(g1),st_asewkt(g2))) from temp;st_astext | st_astext --------------------------+------------------------------- GEOMETRYCOLLECTION EMPTY | POLYGON(( .... )) (1 row)The resulting (correct) polygon is very small (a total area of 0.00048828125, using UTM coordinates), so maybe there's a problem with that? The result of st_overlaps(g1,g2) is true for the same data that cause this problem.I could email someone the geometries if that would help. Regards, MikeHi Mike,I think you'll have to post the geometries if you want someone to help you. If they are large then place them in a text file and send it to the list as a zipped/gzipped attachment.Oh, and don't forget the output of "SELECT postgis_full_version()" while you're at it :)ATB, Mark.
Here they are attached - both as text and as binary within an sql statement that replicates the results of the example describe above.
postgis_full_version (from the yum repo on Fedora 10, x86_64):
postgis_full_version
-------------------------------------------------------------------------------------
POSTGIS="1.3.5" GEOS="3.0.3-CAPI-1.4.2" PROJ="Rel. 4.6.1, 21 August
2008" USE_STATS
g1g2.sql.gz
Description: GNU Zip compressed data
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