[SCM] PostGIS branch master updated. 3.6.0rc2-170-g7dc8c00b7
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- Log -----------------------------------------------------------------
commit 7dc8c00b77b76f584ef5746b97a54b72a7d1caee
Author: Darafei Praliaskouski <me at komzpa.net>
Date: Thu Oct 30 21:31:00 2025 +0400
[doc][topology] Meaning of topology.next_left_edge and topology.next_right_edge links
Closes #5109
diff --git a/NEWS b/NEWS
index 0c485943c..488f86f81 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,7 @@ xxxx/xx/xx
- #5950, Document POSTGIS_REGRESS_DB_OWNER for sandboxed regression roles (Darafei Praliaskouski)
- #4332, Clarify the scope of several Function Reference categories (Darafei Praliaskouski)
- #4222, [raster] ST_DumpAsPolygons honours PostgreSQL interrupts (Darafei Praliaskouski)
+ - #5109, Document the meaning of topology.next_left_edge and topology.next_right_edge links (Darafei Praliaskouski)
* Bug Fixes *
diff --git a/doc/extras_topology.xml b/doc/extras_topology.xml
index 01f07538d..a3846708b 100644
--- a/doc/extras_topology.xml
+++ b/doc/extras_topology.xml
@@ -17,9 +17,27 @@ how is it used, and various FOSS4G tools that support it in <link xlink:href="ht
<para>Details of this project can be found at <link xlink:href="http://trac.osgeo.org/postgis/wiki/UsersWikiPostgisTopology">PostGIS Topology Wiki</link></para>
<para>All functions and tables associated with this module are installed in a schema called <varname>topology</varname>.</para>
<para>Functions that are defined in SQL/MM standard are prefixed with ST_ and functions specific to PostGIS are not prefixed.</para>
- <para>Topology support is build by default starting with PostGIS 2.0, and can be disabled specifying --without-topology configure option at build time as described in <xref linkend="postgis_installation"/></para>
+ <para>Topology support is build by default starting with PostGIS 2.0, and can be disabled specifying --without-topology configure option at build time as described in <xref linkend="postgis_installation"/></para>
- <section xml:id="Topology_Types">
+ <section xml:id="Topology_PrimitiveTables">
+ <title>Topology Primitive Tables</title>
+ <para>The core primitives of any topology are stored in the <varname>edge_data</varname>, <varname>node</varname>, and <varname>face</varname> tables that live in the schema created by <xref linkend="CreateTopology"/>. Each row of <varname>edge_data</varname> represents an oriented edge: it records a directed curve from <varname>start_node</varname> to <varname>end_node</varname> together with the identifier of the face encountered on the left of that direction (<varname>left_face</varname>) and the face encountered on the right (<varname>right_face</varname>). The same geometric segment may therefore appear twice—once for each orientation—when it belongs to two faces.</para>
+ <para>The <varname>next_left_edge</varname> and <varname>next_right_edge</varname> columns complete this orientation information by encoding how to keep walking around a face. They store signed integers whose absolute value is the identifier of the next oriented edge and whose sign determines whether the stored orientation has to be followed as-is or reversed when traversing. Formally, the following rules hold for every edge <varname>e</varname>:</para>
+ <itemizedlist>
+ <listitem>
+ <para><varname>abs(next_left_edge)</varname> is the identifier of the edge reached by continuing around the face that lies to the left of <varname>e</varname>. If the value is positive the walk continues from the end node of <varname>e</varname> along the stored orientation of the referenced edge; if it is negative the referenced edge must be followed backwards so that the shared face remains on the walker’s left.</para>
+ </listitem>
+ <listitem>
+ <para><varname>abs(next_right_edge)</varname> analogously follows the boundary of the face located on the right of <varname>e</varname>. A positive value means that the next edge is taken with its recorded orientation starting from the end node of <varname>e</varname>, whereas a negative value instructs to traverse the referenced edge in reverse, starting from its end node, so that the right-hand face is preserved.</para>
+ </listitem>
+ <listitem>
+ <para>A zero value indicates that the edge is dangling on the corresponding side (for example an isolated edge whose incident face is the universal face <varname>0</varname>). The <varname>abs_next_left_edge</varname> and <varname>abs_next_right_edge</varname> columns exposed by the <varname>edge</varname> view are convenience projections of these absolute values.</para>
+ </listitem>
+ </itemizedlist>
+ <para>This representation is a variant of a doubly connected edge list and is exploited by many topology routines. Functions such as <xref linkend="GetRingEdges"/> and <xref linkend="ValidateTopology"/> rely on it to reconstruct face boundaries and to diagnose inconsistencies—hence the “invalid next_left_edge” and “invalid next_right_edge” diagnostics reported during validation. Constructors like <xref linkend="AddEdge"/> initialise the <varname>next_*</varname> attributes with trivial self references, while editing routines including <xref linkend="ST_AddEdgeModFace"/> and <xref linkend="ST_RemEdgeModFace"/> update the links as edges are inserted or removed. Other bulk operations (for example <xref linkend="TopologyPolygonize"/>) may intentionally leave the fields unset, which is why the documentation flags their behaviour explicitly.</para>
+ </section>
+
+ <section xml:id="Topology_Types">
<title>Topology Types</title><info>
<abstract>
<para>This section lists the PostgreSQL data types installed by PostGIS Topology. Note we describe the casting behavior of these which is very
diff --git a/topology/test/regress/nextedge_signs.sql b/topology/test/regress/nextedge_signs.sql
new file mode 100644
index 000000000..1c315086f
--- /dev/null
+++ b/topology/test/regress/nextedge_signs.sql
@@ -0,0 +1,15 @@
+set client_min_messages to ERROR;
+
+SELECT topology.CreateTopology('signed_edges', 0) > 0;
+
+SELECT 'E1', topology.AddEdge('signed_edges', 'LINESTRING(0 0, 1 0)');
+SELECT 'E2', topology.AddEdge('signed_edges', 'LINESTRING(1 0, 1 1)');
+
+SELECT 'sign-consistency', bool_and(next_left_edge = -next_right_edge)
+ FROM signed_edges.edge;
+
+SELECT 'absolute-id',
+ array_agg(edge_id::text || ':' || abs(next_left_edge)::text ORDER BY edge_id)
+ FROM signed_edges.edge;
+
+SELECT topology.DropTopology('signed_edges');
diff --git a/topology/test/regress/nextedge_signs_expected b/topology/test/regress/nextedge_signs_expected
new file mode 100644
index 000000000..fd8f26bc5
--- /dev/null
+++ b/topology/test/regress/nextedge_signs_expected
@@ -0,0 +1,6 @@
+t
+E1|1
+E2|2
+sign-consistency|t
+absolute-id|{1:1,2:2}
+Topology 'signed_edges' dropped
diff --git a/topology/test/tests.mk b/topology/test/tests.mk
index aa1a67526..383e38ccf 100644
--- a/topology/test/tests.mk
+++ b/topology/test/tests.mk
@@ -47,6 +47,7 @@ TESTS += \
$(top_srcdir)/topology/test/regress/legacy_query.sql \
$(top_srcdir)/topology/test/regress/legacy_validate.sql \
$(top_srcdir)/topology/test/regress/maketopologyprecise.sql \
+ $(top_srcdir)/topology/test/regress/nextedge_signs.sql \
$(top_srcdir)/topology/test/regress/polygonize.sql \
$(top_srcdir)/topology/test/regress/populate_topology_layer.sql \
$(top_srcdir)/topology/test/regress/removeunusedprimitives.sql \
-----------------------------------------------------------------------
Summary of changes:
NEWS | 1 +
doc/extras_topology.xml | 24 +++++++++++++++++++++---
topology/test/regress/nextedge_signs.sql | 15 +++++++++++++++
topology/test/regress/nextedge_signs_expected | 6 ++++++
topology/test/tests.mk | 1 +
5 files changed, 44 insertions(+), 3 deletions(-)
create mode 100644 topology/test/regress/nextedge_signs.sql
create mode 100644 topology/test/regress/nextedge_signs_expected
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