On Nov 28, 2006, at 8:24 AM, Tom Lane wrote:
"Gopal" <gopal@xxxxxxxxxxxxxx> writes:
This is the query and the schema....
...
select
sum(area(intersection(snaptogrid(chunkgeometry,0.00000001),
GeometryFromText('POLYGON((-0.140030845589332
50.8208343077265,-0.138958398039148
50.8478005422809,-0.0963639712296823
50.8471133071392,-0.0974609286275892
50.8201477285483,-0.140030845589332
50.8208343077265))',4326))) * 100/ (0.00114901195862628)) as
percentCover,
So evidently area(intersection(snaptogrid(...))) takes about 300
microsec per row. The PostGIS hackers would have to comment on
whether
that seems out-of-line or not, and whether you can make it faster.
This is consistent with the typical cost for GIS geometry ops -- they
are relatively expensive. When running queries against PostGIS
fields for our apps, about half the CPU time will be spent inside the
geometry ops. Fortunately, there is significant opportunity for
improvement in the performance of the underlying code if anyone found
the time to optimize (and uglify) it for raw speed.
Cheers,
J. Andrew Rogers
