Given a hemispherical surface, the challenge is to create a parametric normal plane (driven by azimuth [sets `longitude'] and zenith [sets `lattitude'] angles) with the smallest possible number of features or construction elements. The set of features will possess an axis which forces the normal reference plane.
One solution is illustrated below. I suspect there is a simpler way.
Thanks in advance for any constructive suggestions (pun intended).
You might use a 3D sketch.