[PD] cart2sph

[Mathieu Bouchard]

On Thu, 21 Nov 2002 bbogart at ryerson.ca wrote:

> I'm very confused by the values given by cart2sph in
> zexy 1.1. They conflict with my original expr based
> equation.
> So If I have x=5, y=5 and z=5
> cart2sph gives me:
> r=8.66, phi=0.78, theta=0.61
> In my own implementation I get:
> r=8.66, theta=0.955, phi=0.78
> [...]
> Close, but not quite?! sorry my trig is not the
> best. Can anyone give me a hand with whats going on?

There are two common kinds of spherical coordinates. Some people use 
longitude&latitude, and some people use longitude&colatitude. Latitude
ranges from -Pi/2 to +Pi/2, and Colatitude ranges from 0 to Pi.

Your theta is colatitude, so your point is 0.955 radians south from the
north pole. Cart2sph's theta is latitude, so your point is 0.61 radians
north of the equator. If values were exact, .61+.955 = Pi/2 radians, the
angle from equator to north pole.

________________________________________________________________
Mathieu Bouchard                       http://artengine.ca/matju