Hi Atul,
are you really sure, you want to union all geometries of the three
tables into one big multipolygon? It seems to me that this might be a
little bit too complex and big...
But, if you really want to union all these geometries (and I am not
sure, if this would really be your plan - because maybe you are mistaken
that union in PostGIS means the same as in ArcGIS??), then I would split
the query again to first do the union of the first two tables, while
immediately dumping the resulting multipolygon into the consisting
single polygons, and next, I would go for the union with the third
table. The queries could look like this:
select (st_dump(st_union(t1.geometry, t2.geometry))).geom as geometry
into new_table from TEMP_OUTPUTTREE_2 t1, TEMP_OUTPUTTREE2_4 t2;
select (st_dump(st_union(nt.geometry, t3.geometry))).geom as geometry
from new_table nt, TEMP_OUTPUTTREE_5 t3;
I don't know if st_union is using the spatial index. If the answer would
be yes, it might be useful to create one on the new_table. But,
depending on the size of your tables, I am afraid, that the queries will
still be much slower than your intersection-queries.
Good luck and regards,
Birgit.
Am 24.11.2011 07:37, schrieb Atul Kumar:
Hi Birgit,
Now its taking less time as compare to previous one.
One more help.
Is there any way to optimize this query because its also taking long
time to execute.
select st_union (st_union (t1.geometry, t2.geometry), t3.geometry)
geometry from TEMP_OUTPUTTREE_2 t1,TEMP_OUTPUTTREE2_4 t2,
TEMP_OUTPUTTREE_5 t3
Thanks
Atul
*From:*postgis-users-boun...@postgis.refractions.net
[mailto:postgis-users-boun...@postgis.refractions.net] *On Behalf Of
*Birgit Laggner
*Sent:* Wednesday, November 23, 2011 6:07 PM
*To:* postgis-users@postgis.refractions.net
*Subject:* Re: [postgis-users] Help me.
Hallo Atul,
perhaps, I would split the query in two queries, because otherwise I
think it might be difficult to use a spatial index on the second
intersection. The queries could be like this:
--create a spatial index on each input table:
create index temp_outputtree_2_gist_geometry on temp_outputtree_2
using gist(geometry);
create index temp_outputtree2_4_gist_geometry on temp_outputtree2_4
using gist(geometry);
create index temp_outputtree_5_gist_geometry on temp_outputtree_5
using gist(geometry);
--intersection of the first 2 tables using the spatial index, writing
the result of it into a new table:
select st_intersection(t1.geometry,t2.geometry) as geometry into
new_table from TEMP_OUTPUTTREE_2 t1 inner join TEMP_OUTPUTTREE2_4 t2
on t1.geometry && t2.geometry where
st_intersects(t1.geometry,t2.geometry);
--create a spatial index on the new geometries of the first intersection:
create index new_table_gist_geometry on new_table using gist(geometry);
--intersection with the third table:
select st_intersection(nt.geometry,t3.geometry) as geometry from
new_table nt inner join TEMP_OUTPUTTREE_5 t3 on nt.geometry &&
t3.geometry where st_intersects(nt.geometry,t3.geometry);
Hope that helps,
Birgit.
Am 23.11.2011 13:16, schrieb Atul Kumar:
Hi All,
I am trying to intersection multiple sets of geographical data using
ST_intersection function. But query execution time is long.
My Query is :
select st_intersection (st_intersection (t1.geometry, t2.geometry),
t3.geometry) geometry from TEMP_OUTPUTTREE_2 t1,TEMP_OUTPUTTREE2_4 t2,
TEMP_OUTPUTTREE_5 t3
I am having three table its having geometry data. I want to intersect
operation on those data.
Please suggest, Is there any optimal way to get the intersection with
less execution time?
Thanks
Atul Kumar
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