[postgis-tickets] [SCM] PostGIS branch master updated. 3.1.0rc1-196-g8fbce9c
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Wed Jun 2 10:49:39 PDT 2021
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commit 8fbce9cc5e1a4fa37f1a2019534227350eb3fac4
Author: Martin Davis <mtnclimb at gmail.com>
Date: Wed Jun 2 10:49:33 2021 -0700
Improve doc ST_AsGeoJSON section
diff --git a/doc/reference_output.xml b/doc/reference_output.xml
index 8c7cb4f..db71a5c 100644
--- a/doc/reference_output.xml
+++ b/doc/reference_output.xml
@@ -548,7 +548,7 @@ F000000000000000000000000000000000000000000000000');
<refnamediv>
<refname>ST_AsGeoJSON</refname>
- <refpurpose>Return the geometry as a GeoJSON element.</refpurpose>
+ <refpurpose>Return a geometry as a GeoJSON element.</refpurpose>
</refnamediv>
<refsynopsisdiv>
@@ -578,12 +578,14 @@ F000000000000000000000000000000000000000000000000');
<refsection>
<title>Description</title>
- <para>Return the geometry as a GeoJSON "geometry" object, or the row as a GeoJSON "feature" object. (Cf <ulink
- url="https://tools.ietf.org/html/rfc7946">GeoJSON specifications RFC 7946</ulink>). 2D and 3D Geometries are both supported. GeoJSON only support SFS 1.1 geometry types (no curve support for example).</para>
+ <para>Returns a geometry as a GeoJSON "geometry", or a row as a GeoJSON "feature".
+ (See the <ulink url="https://tools.ietf.org/html/rfc7946">GeoJSON specifications RFC 7946</ulink>).
+ 2D and 3D Geometries are both supported.
+ GeoJSON only support SFS 1.1 geometry types (no curve support for example).</para>
<para>The <varname>maxdecimaldigits</varname> argument may be used to reduce the maximum number of decimal places used in output (defaults to 9). If you are using EPSG:4326 and are outputting the geometry only for display, <varname>maxdecimaldigits</varname>=6 can be a good choice for many maps.</para>
- <para>The <varname>options</varname> argument could be used to add BBOX or CRS in GeoJSON output:
+ <para>The <varname>options</varname> argument can be used to add BBOX or CRS in GeoJSON output:
<itemizedlist>
<listitem>
<para>0: means no option</para>
@@ -607,6 +609,25 @@ F000000000000000000000000000000000000000000000000');
</itemizedlist>
</para>
+ <para>The GeoJSON specification states that polygons are oriented using the Right-Hand Rule,
+ and some clients require this orientation.
+ This can be ensured by using <xref linkend="ST_ForcePolygonCCW"/>.
+ The specification also requires that geometry be in the WGS84 coordinate system
+ (SRID = 4326).
+ If necessary geometry can be projected into WGS84 using <xref linkend="ST_Transform"/>:
+ <code>ST_Transform( geom, 4326 )</code>.
+ </para>
+
+ <para>GeoJSON can be tested and viewed online at <ulink url="http://geojson.io/">geojson.io</ulink>
+ and <ulink url="http://geojson.io/">geojsonlint.com</ulink>.
+ It is widely supported by web mapping frameworks:
+ <itemizedlist>
+ <listitem><para><ulink url="https://openlayers.org/en/latest/examples/geojson.html">OpenLayers GeoJSON Example</ulink></para></listitem>
+ <listitem><para><ulink url="https://leafletjs.com/examples/geojson/">Leaflet GeoJSON Example</ulink></para></listitem>
+ <listitem><para><ulink url="https://www.mapbox.com/mapbox-gl-js/example/multiple-geometries/">Mapbox GL GeoJSON Example</ulink></para></listitem>
+ </itemizedlist>
+ </para>
+
<para>Availability: 1.3.4</para>
<para>Availability: 1.5.0 geography support was introduced.</para>
<para>Changed: 2.0.0 support default args and named args.</para>
@@ -618,59 +639,57 @@ F000000000000000000000000000000000000000000000000');
<refsection>
<title>Examples</title>
- <para>GeoJSON format is popular among web mapping frameworks.
- <itemizedlist>
- <listitem><para><ulink url="https://openlayers.org/en/latest/examples/geojson.html">OpenLayers GeoJSON Example</ulink></para></listitem>
- <listitem><para><ulink url="https://leafletjs.com/examples/geojson/">Leaflet GeoJSON Example</ulink></para></listitem>
- <listitem><para><ulink url="https://www.mapbox.com/mapbox-gl-js/example/multiple-geometries/">Mapbox GL GeoJSON Example</ulink></para></listitem>
- </itemizedlist>
- </para>
- <para>You can test and view your GeoJSON data online on <ulink url="http://geojson.io/">geojson.io</ulink>.</para>
-
-<para>To build FeatureCollection:</para>
-<programlisting>select json_build_object(
+<para>Generate a FeatureCollection:</para>
+<programlisting>SELECT json_build_object(
'type', 'FeatureCollection',
'features', json_agg(ST_AsGeoJSON(t.*)::json)
)
-from ( values (1, 'one', 'POINT(1 1)'::geometry),
+FROM ( VALUES (1, 'one', 'POINT(1 1)'::geometry),
(2, 'two', 'POINT(2 2)'),
(3, 'three', 'POINT(3 3)')
) as t(id, name, geom);</programlisting>
<screen>{"type" : "FeatureCollection", "features" : [{"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "properties": {"id": 1, "name": "one"}}, {"type": "Feature", "geometry": {"type":"Point","coordinates":[2,2]}, "properties": {"id": 2, "name": "two"}}, {"type": "Feature", "geometry": {"type":"Point","coordinates":[3,3]}, "properties": {"id": 3, "name": "three"}}]}</screen>
-<para>To get Features as records:</para>
+<para>Generate a Feature:</para>
<programlisting>SELECT ST_AsGeoJSON(t.*)
-FROM (VALUES
- (1, 'one', 'POINT(1 1)'::geometry),
- (2, 'two', 'POINT(2 2)'),
- (3, 'three', 'POINT(3 3)'))
-AS t(id, name, geom);</programlisting>
+FROM (VALUES (1, 'one', 'POINT(1 1)'::geometry)) AS t(id, name, geom);</programlisting>
<screen> st_asgeojson
-----------------------------------------------------------------------------------------------------------------
{"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "properties": {"id": 1, "name": "one"}}
- {"type": "Feature", "geometry": {"type":"Point","coordinates":[2,2]}, "properties": {"id": 2, "name": "two"}}
- {"type": "Feature", "geometry": {"type":"Point","coordinates":[3,3]}, "properties": {"id": 3, "name": "three"}}
</screen>
-<para>Don't forget to transform your data to WGS84 longitude, latitude to conform with RFC7946:</para>
+<para>An alternate way to generate Features with an <varname>id</varname> property
+is to use JSONB functions and operators:</para>
+ <programlisting>SELECT jsonb_build_object(
+ 'type', 'Feature',
+ 'id', id,
+ 'geometry', ST_AsGeoJSON(geom)::jsonb,
+ 'properties', to_jsonb( t.* ) - 'id' - 'geom'
+ ) AS json
+FROM (VALUES (1, 'one', 'POINT(1 1)'::geometry)) AS t(id, name, geom);</programlisting>
+<screen> json
+-----------------------------------------------------------------------------------------------------------------
+ {"id": 1, "type": "Feature", "geometry": {"type": "Point", "coordinates": [1, 1]}, "properties": {"name": "one"}}
+</screen>
+
+<para>Don't forget to transform your data to WGS84 longitude, latitude to conform with the GeoJSON specification:</para>
<programlisting>SELECT ST_AsGeoJSON(ST_Transform(geom,4326)) from fe_edges limit 1;</programlisting>
<screen> st_asgeojson
-----------------------------------------------------------------------------------------------------------
{"type":"MultiLineString","coordinates":[[[-89.734634999999997,31.492072000000000],
[-89.734955999999997,31.492237999999997]]]}
-(1 row)</screen>
-<para>You can also use it with 3D geometries:</para>
+</screen>
+<para>3D geometries are supported:</para>
<programlisting>SELECT ST_AsGeoJSON('LINESTRING(1 2 3, 4 5 6)');</programlisting>
<screen>{"type":"LineString","coordinates":[[1,2,3],[4,5,6]]}</screen>
</refsection>
<refsection>
<title>See Also</title>
- <para><xref linkend="ST_GeomFromGeoJSON" />, <xref linkend="ST_AsMVT" />, <xref linkend="ST_AsGeobuf" /></para>
+ <para><xref linkend="ST_GeomFromGeoJSON" />, <xref linkend="ST_ForcePolygonCCW" />, <xref linkend="ST_Transform" /> </para>
</refsection>
-
</refentry>
-----------------------------------------------------------------------
Summary of changes:
doc/reference_output.xml | 77 ++++++++++++++++++++++++++++++------------------
1 file changed, 48 insertions(+), 29 deletions(-)
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