- Heliocentric Cartesian - A 3-D orthonormal coordinate system that is primarily intended to
specify with two dimensions a point on the solar disk. The Z axis points toward the observer.
The Y axis lies in the plane defined by the solar spin vector and the Z axis, positive northward.
The X axis is perpendicular to the Y and Z axes, positive toward solar west. Standard
representation for this system is via the point's x and y values, expressed either as physical
distances or as fractions of the solar disk radius.