[Qgis-developer] why Difference takes much more time then Clip?
giohappy at gmail.com
Tue Jul 1 10:37:38 PDT 2014
I'm doing some tests on fTools/Processing spatial operators, with a cover
multilinestring layer and a base polygon layer.
Running the following query on PostGIS I get similar timings with
st_intersection and st_difference:
select l.osm_id,ST_intersection(l.geom,e.geom) as geom from linee_selezione
as l,edifici_buffer as e where ST_Intersects(l.geom, e.geom)
while if I run the Difference tool QGIS chokes and it takes magnitudes of
more time then Clip.
If made both tools as similar as possible, just changing this  line of
code, but the difference in execution time remains big.
I can't find out where is the difference, because both PostGIS and QGIS
base the operations on GEOS.
GEO+ geomatica in Italia http://bit.ly/GEOplus
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