Re: [postgis-users] Point, Polygon - Does not intersects

fLaNsch Mon, 17 Feb 2014 04:16:22 -0800

Hi,

to speed up, "CREATE INDEX name_gist ON table_name USING gist(geom);" is your friend!

If you go for something like this "st_intersect(st_centroid(a.geom) ,.b.geom) " , remember there will be no Index on st_centroid(a.geom) = SLOW!

Better way, in my opinin, create a second centroid table with an index.

Good Luck

Simon

Gesendet: Montag, 17. Februar 2014 um 12:38 Uhr
Von: "Andreas Forø Tollefsen" <[email protected]>
An: "PostGIS Users Discussion" <[email protected]>
Betreff: Re: [postgis-users] Point, Polygon - Does not intersects

Thank you Hugues,

Your suggestion worked. I still have some problems understanding why my query did not work, but I will give it some thought.

Andreas

2014-02-17 12:09 GMT+01:00 Hugues François <[email protected]>:

Hello,

Maybe the issue is the number of polygon which not intersect between your tables : this query will return you all g1 polygon any times it does not intersect one polygon in your g2 table (I don't know if I'm clear enought, but a g1 polygon where g2 exists will also be returned since it does not intersect others g2 polygon)

I think you could try

SELECT name, geom INTO gadm2_level1_union_selected

FROM

(SELECT g1.*, g2.gid AS g2_gid FROM gadm2_level1_union g1

LEFT JOIN gadm2_level2_union g2 ON ST_Intersects(g1.centroid, g2.geom)) foo

WHERE g2_gid is null

Hugues.

From: [email protected] [mailto:[email protected]] On Behalf Of Andreas Forø Tollefsen
Sent: Monday, February 17, 2014 11:49 AM
To: PostGIS Users Discussion
Subject: [postgis-users] Point, Polygon - Does not intersects

Hi,

I am running the current setup:

"POSTGIS="2.0.2 r10789" GEOS="3.4.0dev-CAPI-1.8.0" PROJ="Rel. 4.7.1, 23 September 2009" GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.7.8" (core procs from "2.0.1 r9979" need upgrade) RASTER (raster procs from "2.0.1 r9979" need upgrade)"

I have two tables with geometries. Both include polygons representing administrative units. One at the first level and one at the second level.

I want a table that includes all the second level polygons where available, and where not available I want the first level polygons.

To find the level 1 polygons for filling the gaps where level 2 is N/A, I thought about finding where the centroid of level one polygons does not intersects with the polygons for level 2.

Hence, I tried:

SELECT g1.name, g1.geom INTO gadm2_level1_union_selected FROM gadm2_level1_union g1, gadm2_level2_union g2 WHERE ST_Intersects(g1.centroid, g2.geom)=FALSE;

I also tried the ST_Disjoint(g1.centroid, g2.geom).

My problem is that this is running for ages without finishing. This should be such a simple query, but I have used half of the day running it. If I take the two geometries into PostGIS and run a spatial query to find the points from level 1 not intersecting with polygons of level 2, it takes 15 seconds.

What could be the issue with my query?

Thanks!

Andreas

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Re: [postgis-users] Point, Polygon - Does not intersects

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