<entry>Representation</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry><type>point</type></entry>
        <entry>16 bytes</entry>
        <entry>Point on a plane</entry>
        <entry>(x,y)</entry>
       </row>
       <row>
        <entry><type>line</type></entry>
        <entry>24 bytes</entry>
        <entry>Infinite line</entry>
        <entry>{A,B,C}</entry>
       </row>
       <row>
        <entry><type>lseg</type></entry>
        <entry>32 bytes</entry>
        <entry>Finite line segment</entry>
        <entry>[(x1,y1),(x2,y2)]</entry>
       </row>
       <row>
        <entry><type>box</type></entry>
        <entry>32 bytes</entry>
        <entry>Rectangular box</entry>
        <entry>(x1,y1),(x2,y2)</entry>
       </row>
       <row>
        <entry><type>path</type></entry>
        <entry>16+16n bytes</entry>
        <entry>Closed path (similar to polygon)</entry>
        <entry>((x1,y1),...)</entry>
       </row>
       <row>
        <entry><type>path</type></entry>
        <entry>16+16n bytes</entry>
        <entry>Open path</entry>
        <entry>[(x1,y1),...]</entry>
       </row>
       <row>
        <entry><type>polygon</type></entry>
        <entry>40+16n bytes</entry>
        <entry>Polygon (similar to closed path)</entry>
        <entry>((x1,y1),...)</entry>
       </row>
       <row>
        <entry><type>circle</type></entry>
        <entry>24 bytes</entry>
        <entry>Circle</entry>
        <entry>&lt;(x,y),r&gt; (center point and radius)</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

   <para>
    In all these types, the individual coordinates are stored as
    <type>double precision</type> (<type>float8</type>) numbers.
   </para>

   <para>
    A rich set of functions and operators is available to perform various geometric
    operations such as scaling, translation, rotation, and determining
    intersections.  They are explained in <xref linkend="functions-geometry"/>.
   </para>

   <sect2 id="datatype-geometric-points">
    <title>Points</title>

    <indexterm>
     <primary>point</primary>
    </indexterm>

    <para>
     Points are the fundamental two-dimensional building block for geometric
     types.  Values of type <type>point</type> are specified using either of
     the following syntaxes:

<synopsis>
( <replaceable>x</replaceable> , <replaceable>y</replaceable> )
  <replaceable>x</replaceable> , <replaceable>y</replaceable>
</synopsis>

     where <replaceable>x</replaceable> and <replaceable>y</replaceable> are the respective
     coordinates, as floating-point numbers.
    </para>

    <para>
     Points are output using the first syntax.
    </para>
   </sect2>

   <sect2 id="datatype-line">
    <title>Lines</title>

    <indexterm>
     <primary>line</primary>
    </indexterm>

    <para>
     Lines are represented by the linear
     equation <replaceable>A</replaceable>x + <replaceable>B</replaceable>y + <replaceable>C</replaceable> = 0,
     where <replaceable>A</replaceable> and <replaceable>B</replaceable> are not both zero.  Values
     of type <type>line</type> are input and output in the following form:
<synopsis>
{ <replaceable>A</replaceable>, <replaceable>B</replaceable>, <replaceable>C</replaceable> }
</synopsis>

     Alternatively, any of the following forms can be used for input:

<synopsis>
[ ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> ) ]
( ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> ) )
  ( <replaceable>x1</replaceable> , <replaceable>y1</replaceable> ) , ( <replaceable>x2</replaceable> , <replaceable>y2</replaceable> )
    <replaceable>x1</replaceable> , <replaceable>y1</replaceable>   ,   <replaceable>x2</replaceable> , <replaceable>y2</replaceable>
</synopsis>

     where
     <literal>(<replaceable>x1</replaceable>,<replaceable>y1</replaceable>)</literal>