[postgis-tickets] [SCM] PostGIS branch master updated. 3.2.0-509-gc5b66667b
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- Log -----------------------------------------------------------------
commit c5b66667b58be986ca4999a411988fdf5f3f97bc
Author: Martin Davis <mtnclimb at gmail.com>
Date: Wed Feb 9 13:57:15 2022 -0800
Improve doc SRS section
diff --git a/doc/using_postgis_dataman.xml b/doc/using_postgis_dataman.xml
index 4c6c8ab77..752b80677 100644
--- a/doc/using_postgis_dataman.xml
+++ b/doc/using_postgis_dataman.xml
@@ -1333,8 +1333,46 @@ SELECT valid, reason, ST_AsText(location) AS location
<sect1 id="spatial_ref_sys">
<title>Spatial Reference Systems</title>
- <para><ulink url="https://en.wikipedia.org/wiki/Spatial_reference_system">Spatial Reference Systems</ulink> (SRS)
- define how geometry is referenced to locations on the Earth's surface.</para>
+ <para>A <ulink url="https://en.wikipedia.org/wiki/Spatial_reference_system">Spatial Reference System</ulink> (SRS)
+ (also called a Coordinate Reference System (CRS))
+ defines how geometry is referenced to locations on the Earth's surface.
+ There are three types of SRS:
+ </para>
+ <itemizedlist>
+ <listitem><para>A <emphasis role="bold">geodetic</emphasis> SRS uses angular coordinates
+ (longitude and latitude)
+ which map directly to the surface of the earth.
+ </para></listitem>
+ <listitem><para>A <emphasis role="bold">projected</emphasis> SRS
+ uses a mathematical projection transformation
+ to "flatten" the surface of the spheroidal earth.
+ It assigns location coordinates in a way that allows direct measurement
+ of metrics such as distance, area, and angle.
+ </para></listitem>
+ <listitem><para>A <emphasis role="bold">local</emphasis> SRS
+ is a Cartesian coordinate system which is not referenced to the earth's surface.
+ In PostGIS this is specified by a SRID value of 0.
+ </para></listitem>
+ </itemizedlist>
+ <para>
+ There are many different spatial reference systems in use.
+ Many common SRSes are standardized by the
+ European Petroleum Survey Group in their
+ <ulink url="http://www.epsg.org/">EPSG database</ulink>.
+ For convenience PostGIS (and many other spatial systems) refers to SRS
+ definitions using an integer identifier called a SRID.
+ </para>
+
+ <para>A geometry is associated with a Spatial Reference System by its SRID value,
+ which is accessed by <xref linkend="ST_SRID" />.
+ The SRID can be assigned to a geometry using <xref linkend="ST_SetSRID" />.
+ Some geometry constructor functions allow supplying a SRID
+ (such as <xref linkend="ST_Point" /> and <xref linkend="ST_MakeEnvelope" />).
+ A SRID can be specified in the EWKT format with the
+ <code>SRID=n;</code> prefix.
+ Geometry data can be transformed between different spatial reference systems using
+ <xref linkend="ST_Transform" />.
+ </para>
<sect2 id="spatial_ref_sys_table">
<title>SPATIAL_REF_SYS Table</title>
@@ -1342,9 +1380,7 @@ SELECT valid, reason, ST_AsText(location) AS location
<para>The <varname>SPATIAL_REF_SYS</varname> table used by PostGIS
is an OGC-compliant database table that defines the available
spatial reference systems.
- It holds the numeric IDs and textual descriptions of the coordinate systems.
- The main use is to support transformation (reprojection) between them using
- <xref linkend="ST_Transform" />.
+ It holds the numeric SRIDs and textual descriptions of the coordinate systems.
</para>
<para>The <varname>spatial_ref_sys</varname> table definition is:</para>
@@ -1385,7 +1421,7 @@ SELECT valid, reason, ST_AsText(location) AS location
<listitem>
<para>The ID of the Spatial Reference System as defined by the
Authority cited in the <varname>auth_name</varname>. In the case
- of EPSG, this is where the EPSG projection code would go.</para>
+ of EPSG, this is the EPSG code.</para>
</listitem>
</varlistentry>
@@ -1413,15 +1449,9 @@ SELECT valid, reason, ST_AsText(location) AS location
UNIT["metre",1]
]</programlisting>
- <para>For a listing of EPSG projection codes and their
- corresponding WKT representations, see <ulink
- url="http://www.opengeospatial.org/">http://www.opengeospatial.org/</ulink>.
- For a discussion of SRS WKT in general, see the OpenGIS "Coordinate
- Transformation Services Implementation Specification" at <ulink
- url="http://www.opengeospatial.org/standards">http://www.opengeospatial.org/standards</ulink>.
- For information on the European Petroleum Survey Group (EPSG) and
- their database of spatial reference systems, see <ulink
- url="http://www.epsg.org/">http://www.epsg.org</ulink>.</para>
+ <para>For a discussion of SRS WKT, see the OGC standard <ulink
+ url="https://www.ogc.org/standards/wkt-crs">Well-known text representation of coordinate reference systems</ulink>.
+ </para>
</listitem>
</varlistentry>
@@ -1508,6 +1538,7 @@ VALUES ( 990000,
</programlisting>
</sect2>
+
</sect1>
<!-- ============================================================== -->
<sect1>
-----------------------------------------------------------------------
Summary of changes:
doc/using_postgis_dataman.xml | 61 ++++++++++++++++++++++++++++++++-----------
1 file changed, 46 insertions(+), 15 deletions(-)
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