[postgis-tickets] [SCM] PostGIS branch master updated. 3.2.0alpha1-11-g5b8bb33
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Tue Sep 21 20:27:05 PDT 2021
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- Log -----------------------------------------------------------------
commit 5b8bb33de39731c93b61e8de5e8a78865b1bcb14
Author: Martin Davis <mtnclimb at gmail.com>
Date: Tue Sep 21 20:27:00 2021 -0700
Improve doc for LineString validity
diff --git a/doc/using_postgis_dataman.xml b/doc/using_postgis_dataman.xml
index 8e5ab72..46c7467 100644
--- a/doc/using_postgis_dataman.xml
+++ b/doc/using_postgis_dataman.xml
@@ -13,9 +13,8 @@
standard (SFA) to provide a model for geospatial data.
It defines the fundamental spatial data type of Geometry, with
a set of subtypes that represent various kinds and dimensions of geometric shapes.
- The latest SFA version
- <ulink url="https://portal.ogc.org/files/?artifact_id=25355"><emphasis>Simple Features Access - Part 1: Common architecture v1.2.1</emphasis></ulink>
- adds subtypes for the more complex geometric objects PolyhedralSurfaces, Triangles and TINs.
+ The <ulink url="https://portal.ogc.org/files/?artifact_id=25355"><emphasis>Simple Features Access - Part 1: Common architecture v1.2.1</emphasis></ulink>
+ adds subtypes for the geometric objects PolyhedralSurfaces, Triangles and TINs.
</para>
<para>The geometry types model shapes on the 2-dimensional Cartesian plane
@@ -66,10 +65,23 @@
are defined for each geometry type.
</para>
+ <para>The OGC geometry model defines validity rules for each geometry type.
+ These rules are intended to ensure that geometry represents realistic
+ situations (e.g. it is possible to specify a polygon
+ with a hole lying outside the shell, but this makes no sense geometrically
+ and is thus invalid).
+ However, PostGIS allows storing and manipulating invalid geometry values
+ to allow detecting and fixing them if needed.
+ For more information see <xref linkend="OGC_Validity" />
+ </para>
+
<sect3 id="Point">
<title>Point</title>
<para>A Point is a 0-dimensional geometry that represents a single location in coordinate space.</para>
- <programlisting>POINT (1 2)</programlisting>
+<programlisting>POINT (1 2)
+POINT Z (1 2 3)
+POINT ZM (1 2 3 4)
+</programlisting>
</sect3>
<sect3 id="LineString">
@@ -77,17 +89,19 @@
<para>A LineString is a 1-dimensional line formed by a contiguous sequence of line segments.
Each line segment is defined by two points, with the end point of one segment
forming the start point of the next segment.
- A LineString must have at least two points.
+ An OGC-valid LineString has either zero or two or more points,
+ but PostGIS also allows single-point LineStrings.
LineStrings may cross themselves (self-intersect).
- A LineString is closed if the start and end points are the same.
+ A LineString is <emphasis role="bold">closed</emphasis> if the start and end points are the same.
+ A LineString is <emphasis role="bold">simple</emphasis> if it does not self-intersect.
</para>
- <programlisting>LINESTRING (1 2, 3 4)</programlisting>
+ <programlisting>LINESTRING (1 2, 3 4, 5 6)</programlisting>
</sect3>
<sect3 id="LinearRing">
<title>LinearRing</title>
<para>A LinearRing is a LineString which is closed
- and simple (non-intersecting).</para>
+ and simple.</para>
<programlisting>LINEARRING (0 0 0,4 0 0,4 4 0,0 4 0,0 0 0)</programlisting>
</sect3>
@@ -97,6 +111,7 @@
delimited by an exterior boundary (the shell)
and zero or more interior boundaries (holes).
The boundaries are formed by LinearRings.
+ Holes must not extend outside the shell.
</para>
<programlisting>POLYGON ((0 0 0,4 0 0,4 4 0,0 4 0,0 0 0),(1 1 0,2 1 0,2 2 0,1 2 0,1 1 0))</programlisting>
</sect3>
@@ -126,7 +141,7 @@
<sect3 id="GeometryCollection">
<title>GeometryCollection</title>
<para>A GeometryCollection is a heterogeneous (mixed) collection of geometries.</para>
- <programlisting>GEOMETRYCOLLECTION ( POINT(2 3), LINESTRING(2 3,3 4))</programlisting>
+ <programlisting>GEOMETRYCOLLECTION ( POINT(2 3), LINESTRING(2 3, 3 4))</programlisting>
</sect3>
<sect3 id="PolyhedralSurface">
@@ -134,7 +149,7 @@
<para>A PolyhedralSurface is a contiguous collection of patches or facets which share some edges.
Each patch is a planar Polygon.
If the Polygon coordinates have Z ordinates then the surface is 3-dimensional.</para>
- <programlisting>POLYHEDRALSURFACE (
+ <programlisting>POLYHEDRALSURFACE Z (
((0 0 0, 0 0 1, 0 1 1, 0 1 0, 0 0 0)),
((0 0 0, 0 1 0, 1 1 0, 1 0 0, 0 0 0)),
((0 0 0, 1 0 0, 1 0 1, 0 0 1, 0 0 0)),
@@ -150,10 +165,11 @@
</sect3>
<sect3 id="Tin">
- <title>Tin</title>
- <para>A Tin is a collection of non-overlapping Triangles
- representing a triangulated irregular network.</para>
- <programlisting>TIN( ((0 0 0, 0 0 1, 0 1 0, 0 0 0)), ((0 0 0, 0 1 0, 1 1 0, 0 0 0)) )</programlisting>
+ <title>TIN</title>
+ <para>A TIN is a collection of non-overlapping Triangles representing a
+ <ulink url="https://en.wikipedia.org/wiki/Triangulated_irregular_network">Triangulated Irregular Network</ulink>.
+ </para>
+ <programlisting>TIN Z ( ((0 0 0, 0 0 1, 0 1 0, 0 0 0)), ((0 0 0, 0 1 0, 1 1 0, 0 0 0)) )</programlisting>
</sect3>
@@ -1497,12 +1513,9 @@ gisdb=# SELECT
valid input.</para>
<note>
- <para>Strictly compliant OGC geometries cannot have Z or M values. The
- <link linkend="ST_IsValid">ST_IsValid()</link> function won't consider
- higher dimensioned geometries invalid! Invocations of <link
- linkend="AddGeometryColumn">AddGeometryColumn()</link> will add a
- constraint checking geometry dimensions, so it is enough to specify 2
- there.</para>
+ <para>The <link linkend="ST_IsValid">ST_IsValid()</link>
+ function does not check the Z and M dimensions.
+ </para>
</note>
</sect1>
-----------------------------------------------------------------------
Summary of changes:
doc/using_postgis_dataman.xml | 53 +++++++++++++++++++++++++++----------------
1 file changed, 33 insertions(+), 20 deletions(-)
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