[postgis-users] query multipolygon

[sgrocho2]

I did not do the st_isvalid check on the ST_Buffer, however when I removed
it, the query ran fast (468ms) and gave the correct answer.  We use the
buffer of -1 in order to minimize error in data creation when trying to snap
things up between layers.  For example Zoning is generally derived from the
parcels but at times get out of alignment when parcels are adjusted.  The -1
buffer takes care of the slight amount of movement created by the
adjustment.  In this case with the fish & wildlife data the buffer really
serves no purpose, we can do without it since it is not parcel derived.  Any
ideas on how to best deal with ST_Buffer? 


Paragon Corporation-2 wrote:
> 
> Did you do an ST_IsValid check on the multipolygons or the ST_Buffer. 
> Could
> be the ST_buffer that is the problem. 
> 
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
> sgrocho2
> Sent: Tuesday, June 02, 2009 5:08 PM
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] query multipolygon
> 
> 
> Okay, I did run ST_IsValid() and everything from each of the layers
> returned
> a t.  When visually checking the query results with 167 rows it appears
> that
> the query is only returning rows that intersect the first polygon it
> processes.  Leaving out those rows that only intersect the other 5
> polygons.
> 
> The following image is an example of what is being missed.  The polygons
> outlined in blue are not selected by the query since they only touch one
> of
> the parcel polygons(green).  
> http://www.nabble.com/file/p23840915/missed_features.jpg 
> 
> 
> 
> 
> Paul Ramsey-4 wrote:
>> 
>> 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.
>>>
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>> 
>> 
> 
> --
> View this message in context:
> http://www.nabble.com/query-multipolygon-tp23836573p23840915.html
> Sent from the PostGIS - User mailing list archive at Nabble.com.
> 
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
> 
> 
> 
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
> 
> 

-- 
View this message in context: http://www.nabble.com/query-multipolygon-tp23836573p23842660.html
Sent from the PostGIS - User mailing list archive at Nabble.com.