Heliocentric Radial - A 3-D orthonormalcoordinate system that is primarily intended to specify with two dimensionsa point on the solar disk. The Z axis points toward the observer. The Y axislies in th
e plane defined by the solar spin vector and the Z axis, positivenorthward. The X axis is perpendicular to the Y and Z axes, positive towardsolar west. Standard representation for this system is via the point'sdistance rho from the Z axis [Rho = SQRT(x**2 + y**2)] and its phase anglepsi measured counterclockwise from the +Y axis [psi = arctan (-y/x)]