From: Paul Ramsey <pramsey@cleverelephant.ca>
Date: Fri, 15 Jan 2010 18:41:41 +0000 (+0000)
Subject: Short circuit on distance tests: only do full spheroidal calculation where the distan... 
X-Git-Tag: 1.5.0rc1~14
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=721f1bafc2c6b6f2983167b3395ba833aab24e03;p=postgis

Short circuit on distance tests: only do full spheroidal calculation where the distance is near or greater than the tolerance. This will make large st_dwithin() radius searches much faster since points that are well within the radius will not have their full geodetic calculation run, only those that are close to the radius boundary.


git-svn-id: http://svn.osgeo.org/postgis/trunk@5133 b70326c6-7e19-0410-871a-916f4a2858ee
---

diff --git a/liblwgeom/lwgeodetic.c b/liblwgeom/lwgeodetic.c
index ebc1c31fb..0bc74fd79 100644
--- a/liblwgeom/lwgeodetic.c
+++ b/liblwgeom/lwgeodetic.c
@@ -1521,11 +1521,15 @@ static double ptarray_distance_spheroid(const POINTARRAY *pa1, const POINTARRAY
 		getPoint2d_p(pa2, 0, &p);
 		geographic_point_init(p.x, p.y, &g2);
 		/* Sphere special case, axes equal */
+		distance = s->radius * sphere_distance(&g1, &g2);
 		if( use_sphere )
-			distance = s->radius * sphere_distance(&g1, &g2);
+            return distance;
+        /* Below tolerance, actual distance isn't of interest */
+        else if( distance < 0.95 * tolerance )
+            return distance; 
+        /* Close or greater than tolerance, get the real answer to be sure */
 		else
-			distance = spheroid_distance(&g1, &g2, s);
-		return distance;		
+		    return spheroid_distance(&g1, &g2, s);
 	}
 
 	/* Handle point/line case here */
@@ -1575,9 +1579,14 @@ static double ptarray_distance_spheroid(const POINTARRAY *pa1, const POINTARRAY
 				/* Working on a sphere? The answer is correct, return */
 				if( use_sphere )
 				{
-					return distance;
+					return d;
 				}
-				/* On a spheroid? Confirm that we are *actually* closer than tolerance */
+				/* Far enough past the tolerance that the spheroid calculation won't change things */
+				else if( d < tolerance * 0.95 )
+				{
+                    return d;
+			    }
+				/* On a spheroid and near the tolerance? Confirm that we are *actually* closer than tolerance */
 				else
 				{
 					d = spheroid_distance(&g1, &nearest2, s);