[postgis-tickets] [SCM] PostGIS branch master updated. 3.4.0beta2-16-g559c95d85
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- Log -----------------------------------------------------------------
commit 559c95d85564fb74fa9e3b7eafb74851810610da
Author: Martin Davis <mtnclimb at gmail.com>
Date: Wed Aug 2 10:28:20 2023 -0700
Doc edits for cluster functions
diff --git a/doc/reference_cluster.xml b/doc/reference_cluster.xml
index 7b88b6727..509e560f5 100644
--- a/doc/reference_cluster.xml
+++ b/doc/reference_cluster.xml
@@ -35,18 +35,18 @@
<title>Description</title>
<para>
- Returns cluster number for each input geometry, based on a 2D implementation of the
+ A window function that returns a cluster number for each input geometry, using the 2D
<ulink url="https://en.wikipedia.org/wiki/DBSCAN">Density-based spatial clustering of applications with noise (DBSCAN)</ulink>
algorithm. Unlike <xref linkend="ST_ClusterKMeans" />, it does not require the number of clusters to be specified, but instead
- uses the desired <link linkend="ST_Distance">distance</link> (<varname>eps</varname>) and density (<varname>minpoints</varname>) parameters to construct each cluster.
+ uses the desired <link linkend="ST_Distance">distance</link> (<varname>eps</varname>) and density (<varname>minpoints</varname>) parameters to determine each cluster.
</para>
<para>
- An input geometry will be added to a cluster if it is either:
+ An input geometry is added to a cluster if it is either:
<itemizedlist>
<listitem>
<para>
- A "core" geometry, that is within <varname>eps</varname> <link linkend="ST_Distance">distance</link> of at least <varname>minpoints</varname> input geometries (including itself) or
+ A "core" geometry, that is within <varname>eps</varname> <link linkend="ST_Distance">distance</link> of at least <varname>minpoints</varname> input geometries (including itself); or
</para>
</listitem>
<listitem>
@@ -58,15 +58,17 @@
</para>
<para>
- Note that border geometries may be within <varname>eps</varname> distance of core geometries in more than one cluster; in this
- case, either assignment would be correct, and the border geometry will be arbitrarily asssigned to one of the available clusters.
- In these cases, it is possible for a correct cluster to be generated with fewer than <varname>minpoints</varname> geometries.
- When assignment of a border geometry is ambiguous, repeated calls to ST_ClusterDBSCAN will produce identical results if an ORDER BY
- clause is included in the window definition, but cluster assignments may differ from other implementations of the same algorithm.
+ Note that border geometries may be within <varname>eps</varname> distance of core geometries in more than one cluster.
+ Either assignment would be correct, so the border geometry will be arbitrarily asssigned to one of the available clusters.
+ In this situation it is possible for a correct cluster to be generated with fewer than <varname>minpoints</varname> geometries.
+ To ensure deterministic assignment of border geometries
+ (so that repeated calls to ST_ClusterDBSCAN will produce identical results)
+ use an <code>ORDER BY</code> clause in the window definition.
+ Ambiguous cluster assignments may differ from other DBSCAN implementations.
</para>
<note><para>
- Input geometries that do not meet the criteria to join any other cluster will be assigned a cluster number of NULL.
+ Geometries that do not meet the criteria to join any cluster are assigned a cluster number of NULL.
</para></note>
<para role="availability" conformance="2.3.0">Availability: 2.3.0</para>
@@ -76,7 +78,7 @@
<refsection>
<title>Examples</title>
<para>
- Assigning a cluster number to each polygon within 50 meters of each other. Require at least 2 polygons per cluster
+ Clustering polygon within 50 meters of each other, and requiring at least 2 polygons per cluster.
</para>
<informaltable>
<tgroup cols="2">
@@ -87,7 +89,7 @@
<imageobject>
<imagedata fileref="images/st_clusterdbscan01.png" />
</imageobject>
- <caption><para>within 50 meters at least 2 per cluster. singletons have NULL for cid</para></caption>
+ <caption><para>Clusters within 50 meters with at least 2 items per cluster. Singletons have NULL for cid</para></caption>
</mediaobject>
</informalfigure>
<programlisting>SELECT name, ST_ClusterDBSCAN(geom, eps := 50, minpoints := 2) over () AS cid
@@ -130,7 +132,7 @@ WHERE name > '' AND building > ''
<para>
- Combining parcels with the same cluster number into a single geometry. This uses named argument calling
+ A example showing combining parcels with the same cluster number into geometry collections.
</para>
<programlisting>
SELECT cid, ST_Collect(geom) AS cluster_geom, array_agg(parcel_id) AS ids_in_cluster FROM (
@@ -145,8 +147,9 @@ GROUP BY cid;
<para><xref linkend="ST_DWithin"/>,
<xref linkend="ST_ClusterKMeans"/>,
<xref linkend="ST_ClusterIntersecting"/>,
- <xref linkend="ST_ClusterWithin"/>
- <xref linkend="ST_ClusterIntersectingWin"/>
+ <xref linkend="ST_ClusterIntersectingWin"/>,
+ <xref linkend="ST_ClusterWithin"/>,
+ <xref linkend="ST_ClusterWithinWin"/>
</para>
</refsection>
</refentry>
@@ -435,7 +438,7 @@ from
<para>An aggregate function that returns an array of GeometryCollections,
where each collection is a cluster containing some input geometries.
- Clustering partitions the input geometries into sets,
+ Clustering partitions the input geometries into sets
in which each geometry is within the specified <parameter>distance</parameter>
of at least one other geometry in the same cluster.
Distances are Cartesian distances in the units of the SRID.
@@ -498,10 +501,9 @@ GEOMETRYCOLLECTION(LINESTRING(6 6,7 7))
<refsection>
<title>Description</title>
- <para>A window function that returns an integer for each input geometry,
- which is the id of the cluster containing the geometry.
- Clustering partitions the input geometries into sets,
- in which each geometry is within the specified <parameter>distance</parameter>
+ <para>A window function that returns a cluster number for each input geometry.
+ Clustering partitions the geometries into sets
+ in which each geometry is within the specified <varname>distance</varname>
of at least one other geometry in the same cluster.
Distances are Cartesian distances in the units of the SRID.
</para>
-----------------------------------------------------------------------
Summary of changes:
doc/reference_cluster.xml | 42 ++++++++++++++++++++++--------------------
1 file changed, 22 insertions(+), 20 deletions(-)
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