I have used three different sun position methods in POV, and was pleased to find
that "sunpos.inc" was bundled with recent releases of POV. However, until today
I could never get it working properly.

Part of my problem arose from an error in the official documentation of this
macro, at

http://www.povray.org/documentation/view/3.6.1/498/

Here, a cylinder is (supposedly) aligned with the sun-vector, at noon (actually,
two minutes past noon) on June 21, 2000, Greenwich, England. The error occurs
because the cylinder
is improperly rotated. The documentation gives

cylinder{
      <-2,0,0>,<2,0,0>,0.1
      rotate <0, Az-90, Al>  //align cylinder with sun
      texture {...}
   }

but for the cylinder to align properly, one must use, instead,

cylinder{
      <-2,0,0>,<2,0,0>,0.1
      rotate <0, 0, Al>
      rotate <0, Az-90, 0>
   }

Thus, the problem seems to be the old non-commutative rotations in three
dimensions.

It would be nice to fix the documentation.

Cheers,

Russell

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