The length/circumference operator @-@ is
a non-boolean unary operator returning the circumference or
length of an object. In the current implementation,
pgSphere supports only
circumferences of circles, polygons, and boxes. It supports
lengths of lines and paths too. Instead of using the
operator, you can use the functions
circum(object) or
length(object).
Example 5.11. Circumference of a circle
sql> SELECT 180 * ( @-@ scircle '<(0d,20d),30d>' )/ pi() AS circ ;
circ
------
180
(1 row)
Example 5.12. Length of a line
sql> SELECT 180 * ( @-@ sline '(0d,0d,0d),30d' )/ pi() AS length ;
length
--------
30
(1 row)