[postgis-tickets] [SCM] PostGIS branch master updated. 3.3.0rc2-1112-g2fdff25ed
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- Log -----------------------------------------------------------------
commit 2fdff25ed242e6de25690b43472027c050d658bb
Author: Martin Davis <mtnclimb at gmail.com>
Date: Mon Jul 3 21:24:32 2023 -0700
Add ST_CoverageSimplify example and diagram
diff --git a/doc/html/images/Makefile.in b/doc/html/images/Makefile.in
index 1f5313040..85ce22eb5 100644
--- a/doc/html/images/Makefile.in
+++ b/doc/html/images/Makefile.in
@@ -77,6 +77,8 @@ GENERATED_IMAGES= \
st_concavehull03.png \
st_concavehull04.png \
st_convexhull01.png \
+ st_coveragesimplify01.png \
+ st_coveragesimplify02.png \
st_crosses01.png \
st_crosses02.png \
st_crosses03.png \
diff --git a/doc/html/images/wkt/st_coveragesimplify01.wkt b/doc/html/images/wkt/st_coveragesimplify01.wkt
new file mode 100644
index 000000000..dbcefbb69
--- /dev/null
+++ b/doc/html/images/wkt/st_coveragesimplify01.wkt
@@ -0,0 +1 @@
+ArgA;GEOMETRYCOLLECTION (POLYGON ((160 150, 110 130, 90 100, 90 70, 60 60, 50 10, 30 30, 40 50, 25 40, 10 60, 30 100, 30 120, 20 170, 60 180, 90 190, 130 180, 130 160, 160 150), (40 160, 50 140, 66 125, 60 100, 80 140, 90 170, 60 160, 40 160)), POLYGON ((40 160, 60 160, 90 170, 80 140, 60 100, 66 125, 50 140, 40 160)), POLYGON ((110 130, 160 50, 140 50, 120 33, 90 30, 50 10, 60 60, 90 70, 90 100, 110 130)), POLYGON ((160 150, 150 120, 160 90, 160 50, 110 130, 160 150)))
diff --git a/doc/html/images/wkt/st_coveragesimplify02.wkt b/doc/html/images/wkt/st_coveragesimplify02.wkt
new file mode 100644
index 000000000..b987d91ed
--- /dev/null
+++ b/doc/html/images/wkt/st_coveragesimplify02.wkt
@@ -0,0 +1 @@
+Result-thin;MULTIPOLYGON (((160 150, 110 130, 50 10, 10 60, 20 170, 90 190, 160 150), (40 160, 66 125, 90 170, 40 160)), ((40 160, 66 125, 90 170, 40 160)), ((110 130, 160 50, 50 10, 110 130)), ((160 150, 160 50, 110 130, 160 150)))
diff --git a/doc/reference_coverage.xml b/doc/reference_coverage.xml
index 123c28212..b1305b006 100644
--- a/doc/reference_coverage.xml
+++ b/doc/reference_coverage.xml
@@ -125,8 +125,16 @@ SELECT true = ALL (
<refsection>
<title>Description</title>
- <para>A window function which simplifies the edges of polygons in a polygonal coverage using the <ulink url="https://en.wikipedia.org/wiki/Visvalingam%E2%80%93Whyatt_algorithm">Visvalingam–Whyatt algorithm</ulink>.
- The simplified outputs are consisent along shared edges, and still form a valid coverage.</para>
+ <para>A window function which simplifies the edges of polygons in a polygonal coverage.
+ The simplification preserves the coverage topology.
+ This means the simplified output polygons are consisent along shared edges, and still form a valid coverage.
+ </para>
+
+ <para>The simplification uses a variant of the <ulink url="https://en.wikipedia.org/wiki/Visvalingam%E2%80%93Whyatt_algorithm">Visvalingam–Whyatt algorithm</ulink>.
+ The <parameter>tolerance</parameter> parameter has units of distance,
+ and is roughly equal to the square root of triangular areas to be simplified.
+ </para>
+
<note><para>If the input is not a valid coverage there may be unexpected artifacts in the output (such as boundary intersections, or separated boundaries which appeared to be shared).
Use <xref linkend="ST_CoverageInvalidLocations" /> to determine if a coverage is valid.
</para></note>
@@ -137,22 +145,55 @@ SELECT true = ALL (
<refsection>
<title>Examples</title>
+ <informaltable>
+ <tgroup cols="2">
+ <tbody>
+ <row>
+ <entry><para>
+ <informalfigure>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="images/st_coveragesimplify01.png" />
+ </imageobject>
+ <caption><para>The input coverage</para></caption>
+ </mediaobject>
+ </informalfigure>
+ </para></entry>
+ <entry><para>
+ <informalfigure>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="images/st_coveragesimplify02.png" />
+ </imageobject>
+ <caption><para>The simplified coverage</para></caption>
+ </mediaobject>
+ </informalfigure>
+ </para></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+
<programlisting>CREATE TABLE coverage (id integer, geom geometry);
INSERT INTO coverage VALUES
- (1, 'POLYGON((0 0, 10 0, 10.1 5, 10 10, 0 10, 0 0))'),
- (2, 'POLYGON((10 0, 20 0, 20 10, 10 10, 10.1 5, 10 0))'),
- (3, 'POLYGON((20 0, 30 0, 30 10, 20 10, 20 0))');
-
-SELECT id, ST_AsText(ST_CoverageSimplify(geom, 1.0) OVER ())
+ (1, '(POLYGON ((160 150, 110 130, 90 100, 90 70, 60 60, 50 10, 30 30, 40 50, 25 40, 10 60, 30 100, 30 120, 20 170, 60 180, 90 190, 130 180, 130 160, 160 150),
+ (40 160, 50 140, 66 125, 60 100, 80 140, 90 170, 60 160, 40 160))'),
+ (2, 'POLYGON ((40 160, 60 160, 90 170, 80 140, 60 100, 66 125, 50 140, 40 160))'),
+ (3, 'POLYGON ((110 130, 160 50, 140 50, 120 33, 90 30, 50 10, 60 60, 90 70, 90 100, 110 130))'
+ (4, 'POLYGON ((160 150, 150 120, 160 90, 160 50, 110 130, 160 150))'
+ );
+
+SELECT id, ST_AsText(ST_CoverageSimplify(geom, 30) OVER ())
FROM coverage;
id | st_astext
----+---------------------------------------
- 1 | POLYGON((10 0,10 10,0 10,0 0,10 0))
- 2 | POLYGON((10 0,20 0,20 10,10 10,10 0))
- 3 | POLYGON((20 0,30 0,30 10,20 10,20 0))
+ 1 | POLYGON ((160 150, 110 130, 50 10, 10 60, 20 170, 90 190, 160 150), (40 160, 66 125, 90 170, 40 160))
+ 2 | POLYGON ((40 160, 66 125, 90 170, 40 160))
+ 3 | POLYGON ((110 130, 160 50, 50 10, 110 130))
+ 3 | POLYGON ((160 150, 160 50, 110 130, 160 150))
</programlisting>
</refsection>
-----------------------------------------------------------------------
Summary of changes:
doc/html/images/Makefile.in | 2 +
doc/html/images/wkt/st_coveragesimplify01.wkt | 1 +
doc/html/images/wkt/st_coveragesimplify02.wkt | 1 +
doc/reference_coverage.xml | 61 ++++++++++++++++++++++-----
4 files changed, 55 insertions(+), 10 deletions(-)
create mode 100644 doc/html/images/wkt/st_coveragesimplify01.wkt
create mode 100644 doc/html/images/wkt/st_coveragesimplify02.wkt
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