Spherical Coordinates as implemenetd in Geodesica-SFX.
+Z comes out of the screen; +X increases toward the right; +Y increases up.
Phi represents a meridian of longitude. All points with the same Phi lie on the same great circle, which passes through the Zenith(0,0). The range for Phi is 0 to 180, rotating anti-clockwise about the +Y axis from +Z [0,0,1]; and 0 to -180, rotating clockwise about the +Y axis from +Z [0,0,1].
Theta represents a meridian of latitude, measured down the Phi circle from the Zenith, i.e., angle Theta is measured with respect to the Zenith not the equator. The range for Theta is 0 to 180, rotating clockwise about the +X axis. All spherical cooridinates whose Theta=90 lie on the equatorial great circle.