On a recent scene I was working on ( see povray images "If you can't go
to heaven") I was using media inside of a plane. I could only see the media
when the camera is inside the plane and not while outside. Why ?
The plane used is at y*0 with the camera at y*-2 using planar for the
density type. If I put the camera at y*2 or even y*20 with the look_at
at y*-10 to make sure I'm pointed an the surface of the plane the media is
still invisible in the scene.

--
Ken Tyler

tyl### [at] pacbellnet

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Ken wrote:

> On a recent scene I was working on ( see povray images "If you can't go
> to heaven") I was using media inside of a plane. I could only see the media
> when the camera is inside the plane and not while outside. Why ?
> The plane used is at y*0 with the camera at y*-2 using planar for the
> density type. If I put the camera at y*2 or even y*20 with the look_at
> at y*-10 to make sure I'm pointed an the surface of the plane the media is
> still invisible in the scene.
>
> --
> Ken Tyler
>
> tyl### [at] pacbellnet

Perhaps Ken it is because a plane is not a closed container ?

--
Ken Tyler

tyl### [at] pacbellnet

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Ken wrote:
> 
> Ken wrote:
> 
> > On a recent scene I was working on ( see povray images "If you can't go
> > to heaven") I was using media inside of a plane. I could only see the media
> > when the camera is inside the plane and not while outside. Why ?
> > The plane used is at y*0 with the camera at y*-2 using planar for the
> > density type. If I put the camera at y*2 or even y*20 with the look_at
> > at y*-10 to make sure I'm pointed an the surface of the plane the media is
> > still invisible in the scene.
> >
> > --
> > Ken Tyler
> >
> > tyl### [at] pacbellnet
> 
> Perhaps Ken it is because a plane is not a closed container ?
> 
> --
> Ken Tyler
> 
> tyl### [at] pacbellnet


I see you doing your best to stay at the top of the stats!  :-)


Marc
-- 
Marc Schimmler

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On Mon, 18 Jan 1999 02:37:53 -0800, Ken <tyl### [at] pacbellnet> wrote:
>Ken wrote:
>
>> On a recent scene I was working on ( see povray images "If you can't go
>> to heaven") I was using media inside of a plane. I could only see the media
>> when the camera is inside the plane and not while outside. Why ?
>> The plane used is at y*0 with the camera at y*-2 using planar for the
>> density type. If I put the camera at y*2 or even y*20 with the look_at
>> at y*-10 to make sure I'm pointed an the surface of the plane the media is
>> still invisible in the scene.
>>
>> --
>> Ken Tyler
>>
>> tyl### [at] pacbellnet
>
>Perhaps Ken it is because a plane is not a closed container ?

That's about right.  For fun, try putting another object inside the
plane. Then you'll be able to see media from outside the plane, but only 
in the places where the ray ends up hitting the other object (even if
the object itself is completely invisible.)  

POV only calculates media effects along a ray after it determines the 
exit point for the ray.  Planes, being infinite, tend not to have exit 
points unless the ray enters another object or starts from inside the 
plane.  (And not all rays that start inside the plane have exit points:
try pointing your camera parallel to the plane when it's inside for 
another weird effect) To fix this, you might try adding another plane 
with the same normal but situated below the plane you're working with, 
or you might try using a large box.

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That's about the response I expected. Thanks.

--
Ken Tyler

tyl### [at] pacbellnet

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I thought I read somewhere in the doc's that it is calculated if inside a hollow
object,
otherways not, (calculating in and outside)

//Spider

Ron Parker wrote:
> 
> On Mon, 18 Jan 1999 02:37:53 -0800, Ken <tyl### [at] pacbellnet> wrote:
> >Ken wrote:
> >
> >> On a recent scene I was working on ( see povray images "If you can't go
> >> to heaven") I was using media inside of a plane. I could only see the media
> >> when the camera is inside the plane and not while outside. Why ?
> >> The plane used is at y*0 with the camera at y*-2 using planar for the
> >> density type. If I put the camera at y*2 or even y*20 with the look_at
> >> at y*-10 to make sure I'm pointed an the surface of the plane the media is
> >> still invisible in the scene.
> >>
> >> --
> >> Ken Tyler
> >>
> >> tyl### [at] pacbellnet
> >
> >Perhaps Ken it is because a plane is not a closed container ?
> 
> That's about right.  For fun, try putting another object inside the
> plane. Then you'll be able to see media from outside the plane, but only
> in the places where the ray ends up hitting the other object (even if
> the object itself is completely invisible.)
> 
> POV only calculates media effects along a ray after it determines the
> exit point for the ray.  Planes, being infinite, tend not to have exit
> points unless the ray enters another object or starts from inside the
> plane.  (And not all rays that start inside the plane have exit points:
> try pointing your camera parallel to the plane when it's inside for
> another weird effect) To fix this, you might try adding another plane
> with the same normal but situated below the plane you're working with,
> or you might try using a large box.

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On Mon, 18 Jan 1999 22:03:47 +0100, Spider <spi### [at] bahnhofse> wrote:
>I thought I read somewhere in the doc's that it is calculated if inside a hollow
object,
>otherways not, (calculating in and outside)

That is true, too, but the effect I think Ken is seeing is not
simply due to the presence or absence of the 'hollow' keyword.
Try it: make a hollow plane and put media in it.  You won't be
able to see the media.  Add a completely transparent sphere
below the plane, and you'll see a roughly-circular spot of media.

----------------------------
plane {y, 0 hollow pigment {color rgbt 1} interior {media {emission red .1}}}
  
/* uncomment the next line to see the media */
//sphere {-y, .5 pigment {color rgbt 1}}
     
camera {location -8*z look_at 0}
----------------------------

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I know this( I doubt anyone of you would make that mistake) , but what I wondered
about is
what more there is that I have missed... I thought this "feature" was documented ;-)


//Spider
Ron Parker wrote:
> 
> On Mon, 18 Jan 1999 22:03:47 +0100, Spider <spi### [at] bahnhofse> wrote:
> >I thought I read somewhere in the doc's that it is calculated if inside a hollow
object,
> >otherways not, (calculating in and outside)
> 
> That is true, too, but the effect I think Ken is seeing is not
> simply due to the presence or absence of the 'hollow' keyword.
> Try it: make a hollow plane and put media in it.  You won't be
> able to see the media.  Add a completely transparent sphere
> below the plane, and you'll see a roughly-circular spot of media.
> 
> ----------------------------
> plane {y, 0 hollow pigment {color rgbt 1} interior {media {emission red .1}}}
> 
> /* uncomment the next line to see the media */
> //sphere {-y, .5 pigment {color rgbt 1}}
> 
> camera {location -8*z look_at 0}
> ----------------------------

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