A PSphereLens is a special nonlinear lens that doesn’t correspond to any real physical lenses. It’s primarily useful for generating 360-degree wraparound images while avoiding the distortion associated with fisheye images.
A PSphereLens is similar to a cylindrical lens, except it is also curved in the vertical direction. This allows it to extend to both poles in the vertical direction. The mapping is similar to what many modeling packages call a sphere mapping: the x coordinate is proportional to azimuth, while the y coordinate is proportional to altitude.