<h3>distance function</h3>
 Returns the minimum distance (based on spatial ref) between two geometries in projected units.

<h4>Syntax</h4>
<pre>distance( a, b )</pre>

<h4>Arguments</h4>
a &rarr; geometry
b &rarr; geometry

<h4>Example</h4>
<pre> distance( geomFromWKT( 'POINT(4 4)' ) , geomFromWKT( 'POINT(4 8)' ))    &rarr; returns 4</pre>
