In article <3A6231FA.FD3761DD@sunshine.net>, dan williams 
<dan### [at] sunshinenet> wrote:

> I have here a verry interesting little (only happens with particular
> values) bug, it turned up when I started using linux for povray, the
> comments in the file say about everything else I know about it.
> 
> I'd do some debugging if I knew where to start.
> 
> if you see the sphere you are not affected by the problem, if not, you
> are.

This group, povray.unix, is for Unix-specific problems. For help with 
the scene language or a possible bug with the core program, you should 
post to one of the general POV-Ray groups, like povray.newusers, 
povray.advanced-users, or povray.general. I'm forwarding this thread to 
povray.general.

If you put:
#debug concat("rotate < ", str(rbshx, 1, 1), ", ", str(rbshy, 1, 1), ", 
", str(rbshz, 1, 1), ">")
in your scene, you will see that "rgshx" is NaN (Not a Number). The NaN 
gets into the matrix and fouls things up. If you put;
#debug concat("acos(", str((len/2)/0.78, 1, 1), ")\n")
you will see that you are attempting to calculate the arc-sine of 1, 
which seems to be undefined.

Using a macro to detect and work around this case works:
#macro ACos(V) #if(V < 1) acos(V) #else (0) #end #end

#declare rbshx = degrees(ACos((len/2)/0.78));

As I recall, the behavior of the inverse trig functions was one of the 
things that was changed in 3.1...they are more mathematically correct, 
but maybe less useable...

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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