[postgis-users] Problem with ST_WITHIN

[Martin Davis]

Switch the arguments around. 

    ST_covers(A, B) = true iff A covers B 

In other words, ST_covers(LINE, POLYGON) = false, but ST_covers(POLYGON, 
LINE) = true.

In other other words, the order of the arguments for ST_covers should be 
the same as for ST_within, and opposite to ST_contains

Luigi Castro Cardeles wrote:
> Hi list and Martin,
>
> If i use st_covers, the query 1 and 2 return's false.
> After read the blog, i am thinking that covers should return true at 
> that cases.
> query 1:
> select ST_covers
>     (
>         geomfromtext('LINESTRING(10 18, 30 18)',4326),
>         geomfromtext('MULTIPOLYGON (((10 18,30 18,30 12,10 12,10 
> 18)))',4326)
>     )
>
> and
>
> query 2:
> select ST_covers
>     (
>         geomfromtext('POINT(10 18)',4326),
>         geomfromtext('MULTIPOLYGON (((10 18,30 18,30 12,10 12,10 
> 18)))',4326)
>     )
>
>
> select postgis_full_version();
> "POSTGIS="1.3.6" GEOS="3.1.0-CAPI-1.5.0" PROJ="Rel. 4.6.1, 21 August 
> 2008" USE_STATS"
> I am using postgres 8.3.7 version and windows vista os.
>
> I read the release notes and the bug tracker and don't find any bug 
> that fit the problem.
>
> In the meanwhile, i will download the postgres 8.3.8, 8.4.1 and try 
> with newer versions of postgis 1.4.0 etc.
>
> Anyone has any clues?
>
> very thanks for yout help,
> Luigi Castro Cardeles
>
>
> 2009/9/21 Martin Davis <mbdavis at refractions.net 
> <mailto:mbdavis at refractions.net>>
>
>     The OGC definition for Contains and Within have always seemed a
>     bit non-intuitive to me.  They may be theoretically elegant. but
>     they don't really address the most common use case.   (See a blog
>     post on this as:
>      http://lin-ear-th-inking.blogspot.com/2007/06/subtleties-of-ogc-covers-spatial.html).
>      
>
>     That's why JTS, GEOS and PostGIS define the covers() predicate,
>     which has simpler, more intuitive and more practical semantics.
>
>     http://postgis.refractions.net/documentation/manual-1.4/ST_Covers.html
>
>
>     Luigi Castro Cardeles wrote:
>
>         Hi list and Chris,
>
>         this is what i was asking :D
>
>         i was thinking that boundary is part of the geometry, so if
>         there is some geometry on the boundary (in this case, a point
>         on the polygon boundary) then the point is within the polygon.
>         But after your message i read the specs
>         (http://portal.opengeospatial.org/files/?artifact_id=18241)
>         about within, i see the relate and now i understand. Thanks
>         for the hint Chris.
>
>         []'s
>         Luigi Castro Cardeles
>
>
>         2009/9/18 Chris Hermansen <chris.hermansen at timberline.ca
>         <mailto:chris.hermansen at timberline.ca>
>         <mailto:chris.hermansen at timberline.ca
>         <mailto:chris.hermansen at timberline.ca>>>
>
>
>            If it's on the boundary, is it within?
>            Chris Hermansen        chris.hermansen at timberline.ca
>         <mailto:chris.hermansen at timberline.ca>
>            <mailto:chris.hermansen at timberline.ca
>         <mailto:chris.hermansen at timberline.ca>>
>
>            tel+1.604.714.2878 · fax+1.604.733.0631 · mob+1.778.840.4625
>            Timberline Natural Resource Group · www.timberline.ca
>         <http://www.timberline.ca>
>            <http://www.timberline.ca>
>
>            401 · 958 West 8th Avenue  · Vancouver BC · Canada · V5Z 1E5
>
>
>            -----Original Message-----
>            From: Luigi Castro Cardeles <luigi.cardeles at gmail.com
>         <mailto:luigi.cardeles at gmail.com>
>            <mailto:luigi.cardeles at gmail.com
>         <mailto:luigi.cardeles at gmail.com>>>
>
>            Date: Fri, 18 Sep 2009 10:01:32
>            To: PostGIS Users
>         Discussion<postgis-users at postgis.refractions.net
>         <mailto:postgis-users at postgis.refractions.net>
>            <mailto:postgis-users at postgis.refractions.net
>         <mailto:postgis-users at postgis.refractions.net>>>
>            Subject: Re: [postgis-users] Problem with ST_WITHIN
>
>
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>
>     -- 
>     Martin Davis
>     Senior Technical Architect
>     Refractions Research, Inc.
>     (250) 383-3022
>
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022