Two questions:

1. In the MegaPov documentation regarding variable reflection, it states:

-- start quote --
You can make reflection_min less than reflection_max if you want, although
the result is something that doesn't occur in nature.
-- end quote --
Should that read the other way around as the docs indicate that if I'm
looking directly at a plate of glass (for example) I could have no
reflection (reflection_min 0), and if I press my face to the glass and look
at the surface I can get a mirror effect (reflection_max 1) and this would
be reflection_min < reflection_max.

Or am I just misunderstanding the whole thing?

2. Regarding IOR.

Say I am modelling glass, then I would use an IOR of 1.5 which produces the
angular change as light passes into and out of it.
If I want to use blinn highlights, then the example uses an IOR of 20 which
is exceedingly large.  Is this just for the example, or do the blinn
highlights require such a high IOR in reality?

Thanks,
Lee Brown
--
lee### [at] prodigynet

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"Lee Brown" <lee### [at] prodigynet> wrote in message
news:3951557c@news.povray.org...
| Two questions:
|
| 1. In the MegaPov documentation regarding variable reflection, it states:
|
| -- start quote --
| You can make reflection_min less than reflection_max if you want, although
| the result is something that doesn't occur in nature.
| -- end quote --
| Should that read the other way around as the docs indicate that if I'm
| looking directly at a plate of glass (for example) I could have no
| reflection (reflection_min 0), and if I press my face to the glass and look
| at the surface I can get a mirror effect (reflection_max 1) and this would
| be reflection_min < reflection_max.
|
| Or am I just misunderstanding the whole thing?

No, I think the doc can be confusing but it's just one of those things that
could be taken both ways without prior knowlegde.  Either that or I've been
using min and max to mean the wrong things all this time.  Seriously though,
that does seem in error to me.  I think there might have actually been a
switch of the two early on in it's implementation but I don't know.  Minimum
was to mean minimal angle from tangent instead of perpendicular to a surface
perhaps.  I could be mistaken about it, especially since that could have been
about the two types of variable reflection.
What I think is worded in a misleading way is the 'parallel to surface normal'
in relflection_min as opposed to saying tangent to the normal.  And the
reflection_max could say perpendicular to surface normal.  Anyhow, I think
it's all in how a person interprets wording such as that in the doc.

| 2. Regarding IOR.
|
| Say I am modelling glass, then I would use an IOR of 1.5 which produces the
| angular change as light passes into and out of it.
| If I want to use blinn highlights, then the example uses an IOR of 20 which
| is exceedingly large.  Is this just for the example, or do the blinn
| highlights require such a high IOR in reality?

Meant for opaque objects.  Doesn't mean you should use that ior value on
transparent objects.  Far as the reasoning besides I couldn't say.

Bob

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Lee Brown <lee### [at] prodigynet> wrote...
> Two questions:
>
> 1. In the MegaPov documentation regarding variable reflection, it states:
>
> -- start quote --
> You can make reflection_min less than reflection_max if you want, although
> the result is something that doesn't occur in nature.
> -- end quote --

This appears to be a mistake in the documentation.

> 2. Regarding IOR.
>
> Say I am modelling glass, then I would use an IOR of 1.5 which produces
the
> angular change as light passes into and out of it.
> If I want to use blinn highlights, then the example uses an IOR of 20
which
> is exceedingly large.  Is this just for the example, or do the blinn
> highlights require such a high IOR in reality?

When use blinn to realistically model highlights on objects that have an
IOR, continue to use the existing IOR and modify the other parameters of
blinn (brightness and microfacet angle).  The IOR used in the blinn model
comes from the IOR of the surface--it's not just a value that is intended to
be fudged.  The reason that it is so high for metals is that using values
like that produces relatively realistic results for those surfaces.

-Nathan

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