Changes between Initial Version and Version 1 of UsersWikiExamplesFindNearbyLatLon

Timestamp:

07/08/09 15:30:14 (16 years ago)

Author:

pramsey

Comment:

--

UsersWikiExamplesFindNearbyLatLon

@@ +1 @@
+Here's a simple 80/20 solution for people with lon/lat tables of
+points wanting to do distance searches.  It only works for places less
+than 60degrees north or south, and only for points. If you know your
+data is all more southerly than 60d, adjust the constant factor to
+make the index portion of the search more selective (and hence,
+efficient (faster)).
+{{{
+#!sql
+-- 
+-- ST_DWithin_Sphere(lonlat-point, lonlat-point, radius-in-meters) returns boolean
+--
+-- Meters/Degree @ 60N: select 1/distance_sphere('POINT(0 60)','POINT(1 60)') = 1.79866403673916e-05
+--
+CREATE OR REPLACE FUNCTION ST_DWithin_Sphere(geometry, geometry, float8)
+        RETURNS boolean
+        AS '
+            SELECT $1 && ST_Expand($2,$3 * 1.79866403673916e-05) 
+               AND $2 && ST_Expand($1,$3 * 1.79866403673916e-05) 
+               AND ST_Distance_Sphere($1, $2) < $3
+        ' LANGUAGE 'SQL' IMMUTABLE;
+}}}