[postgis-devel] point_in_multipolygon implementation

[Obe, Regina]

Andre,

Interesting - never noticed that was commented out and I was looking at
that section.  That could answer another timing puzzle I had.  I'm not
sure why it is commented out.

Can you tell me how much of a speed difference you get by using 

ST_DWithin vs. decomposing your geometry to a single polygon and using
ST_Contains

Something like

SELECT pt.gid as pointid, poly as polyid
FROM 
poly INNER JOIN points pt
ON ST_DWithin(poly.the_geom, p.the_geom, 0.001)

Thanks,
Regina



-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Mose
Andre
Sent: Thursday, September 11, 2008 3:35 PM
To: postgis-devel at postgis.refractions.net
Subject: [postgis-devel] point_in_multipolygon implementation

In trunk, lwgeom_functions_analytic.c:1397 and thereabouts is a
commented out point_in_multipolygon function.

We have noticed a performance gain by convincing contains
(lwgeom_geos_c:1388) to use the point_in_polygon shortcut, but our
application uses a lot of multipolygons.  Rather than switch the
client code to decompose multipolygons (most of them are a single
polygon anyway) it would be nice to just implement this other
shortcut.

Does anyone know why it's not functional?  Or have any recommendations
on how to fix it up?  I cannot find any discussion on the lists.

Thanks,
Mose

>From lwgeom_functions_analytic.c:

/*
 * return 0 iff point is outside every polygon
 */

/* Not yet functional.

int point_in_multipolygon(LWMPOLY *mpolygon, LWPOINT *point)
{
        int i;

#ifdef PGIS_DEBUG_CALLS
        lwnotice("point_in_multipolygon called.");
#endif
        for(i=1; i<mpolygon->ngeoms; i++)
        {
                if(point_in_polygon((LWPOLY *)mpolygon->geoms[i],
point)!=0) return 1;
        }
        return 0;
}
*/


>From lwgeom_geos_c.c:

        /* Not yet functional
        else if(type1 == MULTIPOLYGONTYPE && type2 == POINTTYPE)
        {
                POSTGIS_DEBUG(3, "Point in MultiPolygon test
requested...short-circuiting.");

                mpoly = lwmpoly_deserialize(SERIALIZED_FORM(geom1));
                point = lwpoint_deserialize(SERIALIZED_FORM(geom2));
                if(point_in_multipolygon(mpoly, point) == 0)
                {
                        PG_FREE_IF_COPY(geom1, 0);
                        PG_FREE_IF_COPY(geom2, 1);
                        lwgeom_release((LWGEOM *)mpoly);
                        lwgeom_release((LWGEOM *)point);
                        PG_RETURN_BOOL(FALSE);
                }
                else
                {
                        PG_FREE_IF_COPY(geom1, 0);
                        PG_FREE_IF_COPY(geom2, 1);
                        lwgeom_release((LWGEOM *)mpoly);
                        lwgeom_release((LWGEOM *)point);
                        PG_RETURN_BOOL(TRUE);
                }
        }
        */
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