[postgis-devel] ST_ContainsProperly

[Paragon Corporation]

Martin,

Thanks I'll add this little tidbit to the docs since I just have the
definition and examples. I have it documented but :( the auto doc builder is
still dead so I guess no one can comment on it easily.

I added updating the Refractions website as a task item.
http://trac.osgeo.org/postgis/ticket/155

Thanks,
Regina
 

-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Martin
Davis
Sent: Tuesday, April 14, 2009 5:04 PM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] ST_ContainsProperly

Here's the description from the JTS PreparedGeometry Javadoc:

    /**
     * Tests whether the base {@link Geometry} properly contains a given
geometry.
     * <p>
     * The <code>containsProperly</code> predicate has the following
equivalent definitions:
     * <ul>
     * <li>Every point of the other geometry is a point of this geometry's
interior.
     * <li>The DE-9IM Intersection Matrix for the two geometries matches
     * <code>[T**FF*FF*]</code>
     * </ul>
     * The advantage to using this predicate is that it can be computed
     * efficiently, with no need to compute topology at individual points.
     * <p>
     * An example use case for this predicate is computing the intersections
     * of a set of geometries with a large polygonal geometry. 
     * Since <tt>intersection</tt> is a fairly slow operation, it can be
more efficient
     * to use <tt>containsProperly</tt> to filter out test geometries which
lie
     * wholly inside the area.  In these cases the intersection is
     * known <i>a priori</i> to be exactly the original test geometry.
     *
     * @param geom the Geometry to test
     * @return true if this Geometry properly contains the given Geometry
     *
     */


Paragon Corporation wrote:
> I was scanning thru the list of functions in PgAdmin that don't have 
> help comments for 1.4  and noticed ST_ContainsProperly.  I presume we 
> want this new function which appears to have been introduced in GEOS 3.1
in the docs?
>
> What exactly does it do that is different from ST_Contains?
>
> Thanks,
> Regina
>
>
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>
>   

--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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