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

[Hugues François]

My english won't help me to explain myself but I'll try ! A picture will :)
 
If I'm looking for polygon which don't intersect poly A, It will return a line each polygon it does not intersect, i.e.for B, D, E and F.
 
In your case it your query won't return you only the lack of polygon but also all g1 polygons which doesn't intersect each g2 ones.
 
Is it clearer ?
 
Hugues.
 
 

________________________________

From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Andreas Forø Tollefsen
Sent: Monday, February 17, 2014 12:38 PM
To: PostGIS Users Discussion
Subject: 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 <hugues.francois at irstea.fr>:


	
	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: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] 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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