atan2 weirdness

[Carsten Haese]

narutocanada at gmail.com wrote:
> hi
> 
> atan2 is supposed to return the angle to x-axis when given y and x, I
> suppose if I take [x,y] to one full circle, I should get 0-360 degree
> back---- but no, I get 3 full revolutions!
> maybe my understanding is wrong.
> 
> from math import *
> 
> def f(ang):
>  a=ang
>  if a>360: a-=360
>  if a>360: a-=360
>  if a<0: a+=360
>  if a<0: a+=360
>  return round(a)
> 
> for i in range(0,360):
>  t=2*pi*i/360.0
>  print i,f(atan2(sin(t),cos(t))*180.0)

Your understanding of atan2 is correct, but your conversion from radians 
to degrees is off by a factor of pi. Since pi is close to 3, you're 
getting what appears to be three full revolutions.

HTH,

--
Carsten Haese
http://informixdb.sourceforge.net