Document ST_Simplify parameter (#2093)

git-svn-id: http://svn.osgeo.org/postgis/trunk@14459 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/reference_processing.xml b/doc/reference_processing.xml
index 17530d0e037ef13be665a242740e1f9ccf0aa488..1d55e736bf36448ff83e8dc63295e0f0b3d1b8ae 100644 (file)
--- a/doc/reference_processing.xml
+++ b/doc/reference_processing.xml
@@ -2689,6 +2689,7 @@ LINESTRING(241.42 38.38,241.8 38.45)
                        <funcdef>geometry <function>ST_Simplify</function></funcdef>
                        <paramdef><type>geometry</type> <parameter>geomA</parameter></paramdef>
                        <paramdef><type>float</type> <parameter>tolerance</parameter></paramdef>
+                       <paramdef><type>boolean</type> <parameter>preserveCollapsed</parameter></paramdef>
                  </funcprototype>
                </funcsynopsis>
          </refsynopsisdiv>
@@ -2701,6 +2702,12 @@ LINESTRING(241.42 38.38,241.8 38.45)
                                any kind of geometry. Since simplification occurs on a
                                object-by-object basis you can also feed a GeometryCollection to
                                this function.</para>
+        
+    <para>The "preserve collapsed" flag will retain objects that would otherwise
+      be too small given the tolerance. For example, a 1m long line simplified with a 10m 
+      tolerance. If the preserve flag is given, the line will not disappear. This flag
+      is useful for rendering engines, to avoid having large numbers of very
+      small objects disappear from a map leaving surprising gaps.</para>
 
                <note><para>Note that returned geometry might lose its
                                simplicity (see <xref linkend="ST_IsSimple" />)</para></note>