I think I figured it out.
At first I thought there might be a problem with the quadrant / sector that the
calculation was done in, then it seemed like it might be anything with a Vec
with a negative x component (because the Strut object is constructed in the +x
direction).

After doing some other simplified experiments, it looks like I need to rotate in
the -y direction.   Perhaps due to the left-handed coordinate system?
Can anyone confirm?

Aside from that, I needed to translate to LastVertex (Point1) rather than
ThisVertex (Point2)

and if Twist is set to -y*RotY, then the Struts follow the spherical curvature
as desired.


Looks like it was a busy weekend here at news.povray.org
I'm glad I got some much needed rest AND (perhaps because of that) unraveled the
whole spherical trigonometry vector rotation translation spaghetti.   :)

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