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PostgreSQL documentation

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Note that the <quote>same as</> operator, <literal>~=</>, represents

the usual notion of equality for the <type>point</type>,

<type>box</type>, <type>polygon</type>, and <type>circle</type> types.

Some of these types also have an <literal>=</> operator, but it compares

Some of these types also have an <literal>=</> operator, but

<literal>=</> compares

for equal <emphasis>areas</> only. The other scalar comparison operators

(<literal>&lt;=</> and so on) likewise compare areas for these types.

</para>

<entry>area</entry>

<entry><literal>area(box '((0,0),(1,1))')</literal></entry>

</row>

<row>

<entry><literal><function>box_intersect</function>(<type>box</>, <type>box</>)</literal></entry>

<entry><type>box</type></entry>

<entry>intersection box</entry>

<entry><literal>box_intersect(box '((0,0),(1,1))',box '((0.5,0.5),(2,2))')</literal></entry>

</row>

<row>

<entry><literal><function>center</function>(<replaceable>object</>)</literal></entry>

<entry><type>point</type></entry>

<entry>center and radius to circle</entry>

<entry><literal>circle(point '(0,0)', 2.0)</literal></entry>

</row>

<row>

<entry><literal><function>circle</function>(<type>polygon</type>)</literal></entry>

<entry><type>circle</type></entry>

<entry>polygon to circle</entry>

<entry><literal>circle(polygon '((0,0),(1,1),(2,0))')</literal></entry>

</row>

<row>

<entry><literal><function>lseg</function>(<type>box</type>)</literal></entry>

<entry><type>lseg</type></entry>

<entry>center of lseg</entry>

<entry><literal>point(lseg '((-1,0),(1,0))')</literal></entry>

</row>

<row>

<entry><literal><function>point</function>(<type>lseg</type>, <type>lseg</type>)</literal></entry>

<entry><type>point</type></entry>

<entry>intersection</entry>

<entry><literal>point(lseg '((-1,0),(1,0))', lseg '((-2,-2),(2,2))')</literal></entry>

</row>

<row>

<entry><literal><function>point</function>(<type>polygon</type>)</literal></entry>

<entry><type>point</type></entry>