I could have sworn the Pov-Ray docs explicitly state that
the left handed system is used by default contrary to what
the rest of the world uses. I'm may be getting old buy my
memory isn't that bad.

Ken Tyler

Roland Mas wrote:

> Dan Connelly <djc### [at] flashnet> writes:
>
> > I said "pseudovector".  A velocity vector, for example, is a real
> > thing.  If I have a right-hand or left-hand coordinate system
> > doesn't matter.  But if I take the cross product of two sides
> > of a cube side in a fashion which yields a normal pointing
> > outside the box in a LHS, when I switch to a RHS the same
> > cross product will yield a normal pointing inside the box.
>
>   Yes, sure.  The whole point is:
>
> POV-Ray uses a right-handed coordinate system whatever your camera
>
> , period.  I know this is going to make the whole crowd hurling mad and
> becoming epileptic and throwing rotten tomatoes at me, but that's the way
> it is.  The coordinate system has *nothing* to do with the way you display
> it.  The cross-product of <x1, y1, z1> by <x2, y2, z2> is <y1*z2-z1*y2,
> z1*x2-x1*z2, x1*y2-y1*x2>, whatever your camera is.  The confusing thing is
> that the POV-Doc says that you can change the coordinate system handedness
> by giving different combinations of up, right and direction vectors, which
> is not true.  I repeat, POV-Ray uses a right-handed coordinate system
> whatever your camera.  You can only change the way the camera looks at the
> scene, in which you can choose to look at it as it is (that is, choose a
> right-handed *camera*) of to flip it left-right (or upside-down, or
> front-back, depending on the camera component you change into minus
> itself).  This is a rendering-only characteristic and has nothing to do
> with the real handedness of the coordinate system, which stays the real
> right-handed system used by every mathematician in the world (or at least,
> every mathematician I have heard of).
>
> > In Physics, this is important when considering conserved
> > quantities like parity.
>
>   I won't deny it.  In fact, I keep saying it: we are in a right-handed
> coordinate system, so the Physics theorems and laws are safe.  Now, you
> just have to take care when you look at your scene...
>
>   Okay, throw the tomatoes.  I won't read here till next Tuesday, so please
> don't waste your ammunition till then, or till you're *really* sure I'm
> wrong, in which case we will probably have an interesting discussion next
> week >:-)
>
> Roland.
> --
> Les francophones m'appellent Roland Mas,
> English speakers call me Rowlannd' Mass,
> Nihongode hanasu hitoha [Lolando Masu] to iimasu.
> Choisissez ! Take your pick ! Erande kudasai !

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