get rid of invalid link and obsolete statements about ST_Collect

git-svn-id: http://svn.osgeo.org/postgis/trunk@15214 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/reference_processing.xml b/doc/reference_processing.xml
index 2b27710f00c65e666661c20533fe2d361ae31e31..84e3ffd2182b2969e02689fd4b1c07b02c9df5f3 100644 (file)
--- a/doc/reference_processing.xml
+++ b/doc/reference_processing.xml
@@ -472,13 +472,10 @@ SELECT ST_ClipByBox2D(the_geom, ST_MakeEnvelope(0,0,10,10)) FROM mytab;
                        input geometries. Output type can be a MULTI* or a
                        GEOMETRYCOLLECTION.</para>
 
-               <note><para>ST_Collect and ST_Union are often interchangeable.
-                       ST_Collect is in general orders of magnitude faster than ST_Union
-                       because it does not try to dissolve boundaries or validate that a constructed MultiPolgon doesn't
-                       have overlapping regions. It merely rolls up
-                       single geometries into MULTI and MULTI or mixed geometry types
-                       into Geometry Collections. Unfortunately geometry collections are
-                       not well-supported by GIS tools. To prevent ST_Collect from
+               <note><para>ST_Collect and ST_Union are often interchangeable except that ST_Collect will always return a GeometryCollection or MULTI geometry
+               and ST_Union may return single geometries when it dissolves boundaries.  ST_Union will also split linestrings at node intersections, whereas ST_Collect
+               will never split linestrings and in turn just return as MULTILINESTRING.
+                        To prevent ST_Collect from
                        returning a Geometry Collection when collecting MULTI geometries,
                        one can use the below trick that utilizes <xref linkend="ST_Dump" /> to expand the
                        MULTIs out to singles and then regroup them.</para></note>
@@ -492,9 +489,8 @@ SELECT ST_ClipByBox2D(the_geom, ST_MakeEnvelope(0,0,10,10)) FROM mytab;
 
          <refsection>
                <title>Examples</title>
-               <para>Aggregate example (<ulink url="http://postgis.refractions.net/pipermail/postgis-users/2008-June/020331.html">http://postgis.refractions.net/pipermail/postgis-users/2008-June/020331.html</ulink>)</para>
-                       <programlisting>SELECT stusps,
-          ST_Multi(ST_Collect(f.the_geom)) as singlegeom
+               <para>Aggregate example</para>
+                       <programlisting>SELECT stusps, ST_Collect(f.the_geom) as singlegeom
         FROM (SELECT stusps, (ST_Dump(the_geom)).geom As the_geom
                                FROM
                                somestatetable ) As f