git-svn-id: http://svn.osgeo.org/postgis/trunk@5161 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/reference_operator.xml b/doc/reference_operator.xml
index 1492110693fa8d13e2cdfb12d03bec2be33a30f6..47bc63f61b8cbeb780646ea874cb2472450d1f4f 100644 (file)
--- 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>