[postgis-users] Help me.

[Atul Kumar]

Hi Birgit,

I also don't know whether st_union is using spatial_index because new to postgis.


I am having GUI which shows the data over map.
Suppose user will make query on table1 and queried data display on  map. Queried data is geometry type data.
Again user will make query on table2 and queried data display on map. Queried data is also geometry type data
Again user will make query on table3 and queried data display on map. Queried data is also geometry type data

At the end I want to union above three queried data and display on map using resultant queried union data.

Please suggest me is there other way to union geometry data.


Thanks
Atul

From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Birgit Laggner
Sent: Thursday, November 24, 2011 2:42 PM
To: postgis-users at postgis.refractions.net
Subject: Re: [postgis-users] Help me.

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-bounces at postgis.refractions.net<mailto:postgis-users-bounces at postgis.refractions.net> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Birgit Laggner
Sent: Wednesday, November 23, 2011 6:07 PM
To: postgis-users at postgis.refractions.net<mailto:postgis-users at 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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