...fog & participating media may not work as expected.

Does anyone know why I get this error message? The camera is not inside
anything and I can't figure out whats wrong.

Cheers,
DS.

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On Thu, 9 Jan 2003 14:27:46 -0000, "DaveS"
<dajs100<replacethiswithan@>york.ac.uk> wrote:
> ...fog & participating media may not work as expected.
>
> Does anyone know why I get this error message? The camera is not inside
> anything and I can't figure out whats wrong.

Do we have to trust you or can you give us some minimal source code to give
you more accurate answer? Do you know plane{} has inside defined? Do you know
it is "half" of whole space?

ABX

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"DaveS
> 
> ...fog & participating media may not work as expected.
> 
> Does anyone know why I get this error message? The camera is not inside
> anything and I can't figure out whats wrong.

If you are not using fog or media ignore the warning. You probably have
a "plane" object in your scene and your camera is inside the normal of
the plane. It could also be that you are using a sphere to mimic the sky
which would also lead to that warning. In either case you can add the
"inverse" keyword to the plane or sphere and that will get rid of that
warning.

-- 
Ken Tyler

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Hi, Dave. Please re-post your question about the error message in the
p.newusers group. Include a *minimal* (makes it easier to debug) scene
in the body of your message which demonstrates what you are describing.
Someone will be able to tell you what it is in your scene that is
generating the error message.

  povray.windows is for POV-Ray for Windows-specific discussion, thanks.

-- 
Alan
ako### [at] povrayorg
a k o n g <at> p o v r a y <dot> o r g


On Thu, 9 Jan 2003 14:27:46 -0000 "DaveS"
<dajs100<replacethiswithan@>york.ac.uk> wrote:

>...fog & participating media may not work as expected.
>
>Does anyone know why I get this error message? The camera is not inside
>anything and I can't figure out whats wrong.

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Ken <tyl### [at] pacbellnet> wrote:
> You probably have a "plane" object in your scene

  A really VFAQ? :)

  One might think *why* does a plane need to be defined as solid (ie.
having an interior, which is actually half of the universe). One
naturally thinks a plane is just an infinitely thin sheet with no
volume.
  If one thinks this way, one forgets that planes are quite handy in
CSG (eg. for cutting parts of an object out) and would be quite useless
for this handy purpose if it was a non-solid object (like a bicubic
patch is).

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Ken wrote:
> If you are not using fog or media ignore the warning. You probably have
> a "plane" object in your scene and your camera is inside the normal of
> the plane. It could also be that you are using a sphere to mimic the sky
> which would also lead to that warning. In either case you can add the
> "inverse" keyword to the plane or sphere and that will get rid of that
> warning.

"hollow" should work too.

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Philippe Debar wrote:
> 
> Ken wrote:
> > If you are not using fog or media ignore the warning. You probably have
> > a "plane" object in your scene and your camera is inside the normal of
> > the plane. It could also be that you are using a sphere to mimic the sky
> > which would also lead to that warning. In either case you can add the
> > "inverse" keyword to the plane or sphere and that will get rid of that
> > warning.
> 
> "hollow" should work too.

It does, but it also confuses the issue of surface normals so I chose not
to use it in my example.

-- 
Ken Tyler

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Philippe Debar <phd### [at] wanadoobe> wrote:
> "hollow" should work too.

  IMHO it's not the best solution.
  You should understand how plane works and it should be completely crystal
clear which side of the plane you are defining is inside and which is
outside. "Fixing" the warning by putting 'hollow' in the plane definition
is more like hiding the problem, not fixing it. It can teach you wrong
principles. You should have a good, real reason to use 'hollow', and IMHO
getting rid of the warning is not one.
  Defining the plane so that the scene is located *outside* it is the best
solution. It helps you visualizing better what's happening.

  A quick recapitulation: The first parameter of 'plane' defines its normal
vector. The normal vector points outside the plane.
  That is, if you for example define a 'plane { z,0 }', then everything
which is located anywhere with a positive z coordinate is outside the plane,
while things located at a negative z coordinate are inside the plane.
'plane { -z,0 }' inverts this.
  The second parameter tells an offset. The plane is translated by this
amount along the normal vector (ie. in the direction of the first parameter).
Usually you want to move the plane backwards, ie. in the opposite direction
of the normal vector (very common when defining floors and walls), which
naturally means that this parameter should be negative.
  Thus, eg. a floor is usually defined like 'plane { y, -5 }', which creates
a plane at y=-5 so that everything above it is outside.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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"Ken" <tyl### [at] pacbellnet> wrote in message
news:3E23DCD8.B37F4AFB@pacbell.net...
> > "hollow" should work too.
>
> It does, but it also confuses the issue of surface normals so I chose not
> to use it in my example.

Yes, the "hollow" keyword is confusing. But I believed the normals were
unaffected. Aren't they? What I understood is that the object still has a
clearly determined outside and inside - hence you can use interior{}and csg,
but you need to hollow the object to fill it with media.

Is there any planned change for that behaviour?

I do not understand why you need "hollow" to use interior{media} and not
(iirc) interior{ior} (And I really mean that I do not understand, not
anything else - there are probably technical reasons, I just do not know
them) . Is there any case where there is an advantage in using an
interior{media} in a non hollow object? BTW I'd be happy to be able to have
an object inside a media to be filled either by it's own media only or with
it's and the surrounding medias without having to use tricky csg.


Povingly,


Philippe

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Stepping in on this little discussion...

"Philippe Debar" <phd### [at] wanadoobe> wrote in message
news:3e24ff65@news.povray.org...
>
> "Ken" <tyl### [at] pacbellnet> wrote in message
> news:3E23DCD8.B37F4AFB@pacbell.net...
> > > "hollow" should work too.
> >
> > It does, but it also confuses the issue of surface normals so I chose
not
> > to use it in my example.
>
> Yes, the "hollow" keyword is confusing. But I believed the normals were
> unaffected. Aren't they? What I understood is that the object still has a
> clearly determined outside and inside - hence you can use interior{}and
csg,
> but you need to hollow the object to fill it with media.

Right.

> Is there any planned change for that behaviour?

Not that I know of, except I'm sure this general subject must have been
talked about in the past. Something of a hierarchy for combining or
separating medias. Those two words would label it well I think, combine or
separate. I haven't looked at the media source code but it doesn't sound
that easy to change. It would mean per object media mixing as is already
done within interiors having more than one media statement present, so it
would need to check all other object interiors.

> I do not understand why you need "hollow" to use interior{media} and not
> (iirc) interior{ior} (And I really mean that I do not understand, not
> anything else - there are probably technical reasons, I just do not know
> them) . Is there any case where there is an advantage in using an
> interior{media} in a non hollow object? BTW I'd be happy to be able to
have
> an object inside a media to be filled either by it's own media only or
with
> it's and the surrounding medias without having to use tricky csg.

It's really a pre-media thing, when 'atmosphere' came along it applied to
that as well; and finally media too, since it could also be global. I
couldn't tell you the exact reasoning but that's probably why 'hollow' is
the defacto way to produce a surface shell rather than the usual solid
object.

As to what you asked there, "Is there any case where there is an advantage
in using an interior{media} in a non-hollow object?", I guess you are saying
again that hollow is redundant if media exists at all on a per object basis.
And you answer your own question in the sense that it would be good to mix
and match medias with more control, and it's CSG or global media that
becomes tricky as it stands now.

--
Farewell,
Bob

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