The binary distance operator <-> is
a non-boolean operator returning the distance between two
objects in radians. Currently,
pgSphere supports only distances
between points, circles, between point and circle, and
between point and line. If the
objects are overlapping, the distance operator returns zero
(0.0).
Example 5.9. Distance between two circles
sql> SELECT 180 * ( scircle '<(0d,20d),2d>' <-> scircle '<(0d,40d),2d>' )
/ pi() AS dist ;
dist
------
16
(1 row)
Example 5.10. Distance between point and line
sql> SELECT 180 * (sline '( 0d, 0d, 0d, XYZ ), 40d ' <-> spoint '( 0d, 90d )')
/ pi() AS dist ;
dist
------
90
(1 row)