spherical pattern creates a one unit radius sphere, with its center at the origin. It is computed
by: value = 1.0-min(1, sqrt(X^2 + Y^2 + Z^2)) It starts at 1.0 at the origin and decreases to a minimum
value of 0.0 as it approaches a distance of 1 unit from the origin in any direction. It remains at 0.0 for all areas
beyond that distance. This pattern was originally created for use with
media but it
may be used anywhere any pattern may be used.