@classmethod<EOL><INDENT>def from_spherical(cls, r=<NUM_LIT:1.0>, alpha=<NUM_LIT:0.0>, delta=<NUM_LIT:0.0>):<DEDENT>
x = r * math.cos(delta) * math.cos(alpha)<EOL>y = r * math.cos(delta) * math.sin(alpha)<EOL>z = r * math.sin(delta)<EOL>return cls(x=x, y=y, z=z)<EOL>
Construct Cartesian vector from spherical coordinates.

        alpha and delta must be in radians.