Chambers <ben### [at] pacificwebguycom> wrote:
> Warp wrote:
> >   You are not understanding.
> >
> >   You said, and I quote: "It's a known aspect of the hardware we use
> > that you should keep your ratios smaller than this to avoid precision
> > errors."
> >   I didn't know that the ratio between double precision floating point
> > numbers must be smaller than 20 millions in order to preserve accuracy.
> > I asked where did you get that number.
>
>
> Thanks for clarifying.  It was a faulty assumption on my part.
>
> It IS true that you should keep your numbers in the same range for the
> greatest accuracy.  As I was unaware of the internal limits imposed by
> POV-Ray, I assumed this range difference was the culprit, and therefore
> I assumed that the limit had been reached.
>
> Really what I should have said was, "It's a known aspect of the hardware
> we use that you should keep your ratios within a reasonable limit to
> avoid precision errors, and I'm assuming that you have reached that limit."
>
> Of course he hadn't yet reached that limit, but instead had run into
> POV's internal limits.
>
> ...Chambers

yes, an example of hardware limits is that, due to limited z buffer
precision, the ratio between far and near clip planes needs to be kept
within certain limits (which vary depending on the accuracy you need). Some
ppl, use a rule of 1:300.
But POV renders to files so no issue with z buffer there.
However the limits of double precision still apply and you can lose accuracy
even at distances that would normally not be considered too large for double
precision, as my paper and "stress test" program show.

cheers,

chris

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dragonmage <dra### [at] gmailcom> wrote:
> yes, an example of hardware limits is that, due to limited z buffer
> precision, the ratio between far and near clip planes needs to be kept
> within certain limits (which vary depending on the accuracy you need). Some
> ppl, use a rule of 1:300.
> But POV renders to files so no issue with z buffer there.

  I think you have some confusions there. Firstly, POV-Ray doesn't use
any Z-buffer of any kind (raytracers don't need those), and secondly,
even if it used one, rendering to a file or to the screen makes no
difference, why would it? It's not like rendering to a file magically
removed the need for Z-buffering compared to rendering to the screen.
(And no, Z-buffering is not automatic/mandatory even if you scanline-render
using 3D hardware. It's perfectly possible to turn the Z-buffer off.)

-- 
                                                          - Warp

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