Thank you everyone for all that help.
I worked out how to do it after re-reading your posts carefully. I had to break
out the geometry/trigonometry skills to derive the angles from xyz coordinates.
there seems to be no other way.
unless there is . . . .

Is there a povray function that returns polar coordinates of a surface's normal?

eg. create a polygon my_polygon at xyz xyz xyz and then ask--

let lat/lon = normal(my_polygon)

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