Transform Cartesian coordinates to spherical

The mapping from three-dimensional Cartesian coordinates to spherical coordinates is

azimuth = atan2(y,x) elevation = atan2(z,sqrt(x.^2 + y.^2)) r = sqrt(x.^2 + y.^2 + z.^2)

The notation for spherical coordinates is not standard. For
the `cart2sph`

function, `elevation`

is
measured from the *x-y* plane. Notice that if ```
elevation
= 0
```

, the point is in the *x-y* plane.
If `elevation = pi/2`

, then the point is on the positive *z*-axis.