In the section on mathematical functions the following is given for atan2:
atan2(x, y) inverse tangent of a/x
I believe the correct version should either be:
atan2(y, x) inverse tangent of y/x
or
atan2(x, y) inverse tangent of x/y
I beleive the documentation was also wrong for 7.2 where it was:
atan2(x, y) inverse tangent of y/x
The postgres functions seems to be the same as glibc function of the same
name when has the following man information:
double atan2(double y, double x);
DESCRIPTION
The atan2() function calculates the arc tangent of the two
variables x and y. It is similar to calculating the arc
tangent of y / x, except that the signs of both arguments
are used to determine the quadrant of the result.