In article <3c5bafb4@news.povray.org> , "JRG" <jrg### [at] hotmailcom> wrote:

> Assuming that divisions by zero have to be avoided, I
> believed that functions in isosurfaces were *parsed* (I know they are
> evaluated during the rendering) before the transformations. I mean, the shape
> (thus the function) does not change if you translate the iso anywhere you
> want.

Ah, now I see your problem.  You completely misunderstand why it sometimes
appears and why not.  Translating does not change anything but the points that
are evaluated.  With some translations you are just lucky that "y" will never
be zero when rendering with a specific resolution.  There is no way to predict
when "y" will be zero and when it will not be.

> I did use divisions by zero many times before, and all I got was weird
> surfaces at most.

You got those because for many other reasons that having nothing to do with
the division by zero.  I.e. if you are referring to MegaPOV, I think it would
crash (on Windows and Linux at least, on Macs division by zero excepts don't
cause programs to be terminated) if there really was a division by zero.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

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