[postgis-devel] ST_ContainsProperly

[Martin Davis]

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