From abefba02042fa4b6c04fa598263871e08082c6d0 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Nicklas=20Av=C3=A9n?= <nicklas.aven@jordogskog.no>
Date: Sun, 24 Jan 2010 09:10:31 +0000
Subject: [PATCH] git-svn-id: http://svn.osgeo.org/postgis/trunk@5161
 b70326c6-7e19-0410-871a-916f4a2858ee

---
 doc/reference_operator.xml | 46 +++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 23 deletions(-)

diff --git a/doc/reference_operator.xml b/doc/reference_operator.xml
index 149211069..47bc63f61 100644
--- a/doc/reference_operator.xml
+++ b/doc/reference_operator.xml
@@ -894,7 +894,7 @@ FROM
 		  <refnamediv>
 			<refname>~=</refname>
 
-			<refpurpose>Returns <varname>TRUE</varname> if the geometry A is the same as B.</refpurpose>
+			<refpurpose>Returns <varname>TRUE</varname> if A's bounding box is the same as B's.</refpurpose>
 		  </refnamediv>
 
 		  <refsynopsisdiv>
@@ -938,39 +938,39 @@ FROM
 		  <refsection>
 			<title>Description</title>
 
-			<para>The <varname>~=</varname> operator returns <varname>TRUE</varname> if geometry A is the same as geometry B.
-			It tests actual geometric equality of two features.  So if A and B are the same feature, vertex-by-vertex, the
-			operator returns <varname>TRUE</varname>.</para>
+			<para>The <varname>~=</varname> operator returns <varname>TRUE</varname> if the bounding box of geometry/geography A
+			is the same as the bounding box of geometry/geography B.</para>
 
 			<note><para>This operand will make use of any indexes that may be available on the
 			  geometries.</para></note>
 
-			 <para>Availability: 1.5.0 support for geography was introduced.</para>
+			 <para>Availability: 1.5.0 changed behavior</para>
 		  </refsection>
-
+		  
+			<warning>
+			  <para>This operator has changed behavior in PostGIS 1.5
+			  from testing for actual geometric equality to only 
+			  checking for bounding box equality. To complicate things 
+			  it also depends on if you have done a hard or soft upgrade 
+			  which behavior your database has. To find out which behavior
+			  your database has you can run the query below.
+				To check for true equality use <xref linkend="ST_OrderingEquals" /> or <xref
+			  linkend="ST_Equals" /> and to check for bounding box equality <xref linkend="ST_Geometry_EQ" />; 
+			  operator is a safer option.</para>
+			  </warning>
 		  <refsection>
 			<title>Examples</title>
+<programlisting>
 
-			<programlisting>SELECT tbl1.column1, tbl2.column1, tbl1.column2 ~= tbl2.column2 AS same
-FROM
-  ( VALUES
-	(1, 'LINESTRING (0 0, 2 2)'::geometry)) AS tbl1,
-  ( VALUES
-	(2, 'LINESTRING (0 0, 1 1, 2 2)'::geometry),
-	(3, 'LINESTRING (2 2, 0 0)'::geometry),
-	(4, 'LINESTRING (0 0, 2 2)'::geometry)) AS tbl2;
-
- column1 | column1 | same
----------+---------+------
-	   1 |       2 | f
-	   1 |       3 | f
-	   1 |       4 | t
-(3 rows)</programlisting>
+select 'LINESTRING(0 0, 1 1)'::geometry ~= 'LINESTRING(0 1, 1 0)'::geometry as equality;
+ equality   |
+-----------------+
+          t    |
+ 			</programlisting>
+			<para>The above can be used to test if you have the new or old behavior of ~= operator.</para>
 		  </refsection>
-
 		  <refsection>
 			<title>See Also</title>
-
 			<para><xref linkend="ST_Equals" />, <xref linkend="ST_OrderingEquals" />, <xref linkend="ST_Geometry_EQ" /></para>
 		  </refsection>
 		</refentry>
-- 
2.40.0