On Fri, 22 Nov 2002, Robert Figura wrote:
On 21 Nov, bbogart@ryerson.ca wrote: PHI is all right, but if: atan2f(a,b) := atan(a/b)
that's almost true, yes.
then THETA is wrong (wrong parameter order), corrected:
It is wrong only if the documentation says it should be otherwise. But colatitude is very often used. For example, when I was in 13th grade we were doing jacobian coordinate transforms, and we learned spherical coordinates using colatitude instead of latitude.
BTW: atan2(a,b) is a standard c function? Makes sense in case b is zero. So i had had no need to implement it myself?
atan2 is a standard C function; it's the only inverse trigonometric function you really need, and all other ones may be derived from it. Atan2 is so convenient. I remember coding it by hand in terms of ATN() when i used the BASIC language long ago.
It is true it works even when b is zero, but there's also another neat feature: it has a 2pi radian range instead of just pi -- it uses both signs of a and b to compute the result.
Mathieu Bouchard http://artengine.ca/matju