I don't want an elliptic sun (part II).... (advanced 3d patch placement )

[Andrea V. <and...@gm...>]

Hello Chriss,

I'm returning to the application for orienting a patch to the viewer
given azimuth and elevation.

Your modification of my setpos(p,dis,az,el) works very fine with a sun image
which has a circular symmetry, 
so, rotation around its perpendicular axis pointing inward,
does not matter very much,

but how could I calculate parameter "angle" (that we haven't included before
in the "move" statement), so the bottom of the patch remains parallel 
to the "xz" plane for every value of azimuth and elevation? (i.e.: in other
words, if I write something into the patch, I would like that the text
remained parallel to the ground)

You are very good at trigonometry, I am sure that this will take just a moment!!

Thank you!!

Andrea