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Some improvements in geometric-operators documentation.

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This commit is contained in:
Tom Lane 2002-08-08 14:29:07 +00:00
parent f84002176f
commit d176fad580
1 changed files with 25 additions and 9 deletions
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34
doc/src/sgml/func.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.108 2002/08/06 05:40:44 ishii Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.109 2002/08/08 14:29:07 tgl Exp $
PostgreSQL documentation
-->
@ -3868,7 +3868,7 @@ SELECT TIMESTAMP 'now';
</row>
<row>
<entry> # </entry>
<entry>Number of points in polygon</entry>
<entry>Number of points in path or polygon</entry>
<entry><literal># '((1,0),(0,1),(-1,0))'</literal></entry>
</row>
<row>
@ -4025,6 +4025,18 @@ SELECT TIMESTAMP 'now';
<entry>length of item</entry>
<entry><literal>length(path '((-1,0),(1,0))')</literal></entry>
</row>
<row>
<entry><function>npoints</function>(path)</entry>
<entry><type>integer</type></entry>
<entry>number of points</entry>
<entry><literal>npoints(path '[(0,0),(1,1),(2,0)]')</literal></entry>
</row>
<row>
<entry><function>npoints</function>(polygon)</entry>
<entry><type>integer</type></entry>
<entry>number of points</entry>
<entry><literal>npoints(polygon '((1,1),(0,0))')</literal></entry>
</row>
<row>
<entry><function>pclose</function>(path)</entry>
<entry><type>path</type></entry>
@ -4040,12 +4052,6 @@ SELECT TIMESTAMP 'now';
<entry><literal>point(lseg '((-1,0),(1,0))',lseg '((-2,-2),(2,2))')</literal></entry>
</row>
]]>
<row>
<entry><function>npoint</function>(path)</entry>
<entry><type>integer</type></entry>
<entry>number of points</entry>
<entry><literal>npoints(path '[(0,0),(1,1),(2,0)]')</literal></entry>
</row>
<row>
<entry><function>popen</function>(path)</entry>
<entry><type>path</type></entry>
@ -4150,7 +4156,7 @@ SELECT TIMESTAMP 'now';
<row>
<entry><function>polygon</function>(<type>box</type>)</entry>
<entry><type>polygon</type></entry>
<entry>12 point polygon</entry>
<entry>4-point polygon</entry>
<entry><literal>polygon(box '((0,0),(1,1))')</literal></entry>
</row>
<row>
@ -4175,6 +4181,16 @@ SELECT TIMESTAMP 'now';
</tgroup>
</table>
<para>
It is possible to access the two component numbers of a <type>point</>
as though it were an array with subscripts 0,1. For example, if
<literal>t.p</> is a <type>point</> column then
<literal>SELECT p[0] FROM t</> retrieves the X coordinate;
<literal>UPDATE t SET p[1] = ...</> changes the Y coordinate.
In the same way, a <type>box</> or an <type>lseg</> may be treated
as an array of two <type>point</>s.
</para>
</sect1>