[postgis-users] query multipolygon

[Paul Ramsey]

Slow-vs-fast I can understand... the spatial index can more
effectively parcel out the problem for processing when the units of
processing are smaller.

Wrong-vs-right I have a problem with. Are your multi-polygons valid?
Run ST_IsValid() on them. It's possible that they are valid taken
separately but invalid when combined (multipolygons are not allowed to
have overlapping components).

Paul

On Tue, Jun 2, 2009 at 11:05 AM, sgrocho2 <sgrocho at gmail.com> wrote:
>
> I am having trouble querying a multipolygon feature intersection with another
> multipolygon feature.  When I execute the query it takes 45 seconds and
> returns and incomplete answer, 167 rows.  If I explode the parcel polygon
> into its 6 parts and then run the same query it takes 5 seconds and returns
> 209 rows which is the correct answer.  Is there a way to write this query to
> return the all the rows without having to first manipulate the data?  The
> same query works fine in SQL Server but we want to use PostGIS. Below is the
> code for each of the Parcel tables they include only one parcel - one with 1
> row, the other with 6 rows.
>
> THIS IS THE SINGLE FEATURE MULTIPOLYGON CODE: 45sec 167 rows
> SELECT DISTINCT g1.objectid As taxpar_id, g1.tax_parcel_num As
> parcel_number, g2.objectid As fw_id, g2.wdfw_phs, g2.wdfw_occur_pt,
> g2.wdfw_haulout, g2.pc_for_fish, g2.wdfw_fish_dist, g2.pc_oaks,
> g2.pc_salmon, g2.wdfw_occur_pl, g2.doh_sf, g2.wdfw_owl, g2.pc_eelgrass,
> g2.pc_hydro, g2.wdfw_sasi
>        FROM loader.single_parcel As g1, loader.potential_fw_habitat_cons_areas_pg
> As g2
>    WHERE (g1.tax_parcel_num = '0618161001' AND
> ST_Intersects(ST_Buffer(g1.Shape,-1), g2.Shape))
>
> THIS IS THE EXPLODED 6 FEATURES CODE: 5sec 209 rows
> SELECT DISTINCT g1.objectid As taxpar_id, g1.tax_parcel_num As
> parcel_number, g2.objectid As fw_id, g2.wdfw_phs, g2.wdfw_occur_pt,
> g2.wdfw_haulout, g2.pc_for_fish, g2.wdfw_fish_dist, g2.pc_oaks,
> g2.pc_salmon, g2.wdfw_occur_pl, g2.doh_sf, g2.wdfw_owl, g2.pc_eelgrass,
> g2.pc_hydro, g2.wdfw_sasi
>        FROM loader.multi_parcel As g1, loader.potential_fw_habitat_cons_areas_pg
> As g2
>    WHERE (g1.tax_parcel_num = '0618161001' AND
> ST_Intersects(ST_Buffer(g1.Shape,-1), g2.Shape))
>
> --
> View this message in context: http://www.nabble.com/query-multipolygon-tp23836573p23836573.html
> Sent from the PostGIS - User mailing list archive at Nabble.com.
>
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