Hi POV-gurus,

A Moray user asked me whether it was possible to create the following
effect:

he wants to create a scene with a floor and a number of reflecting
objects. The objects should not reflect the floor, however, they
should only reflect each other. Is this at all possible? I pretty much
assume it's impossible with the official 3.1, so I'm wondering whether
MegaPOV or SuperPatch or any other patches would allow this.

Thanks,

- Lutz
  email : lut### [at] stmuccom
  Web   : http://www.stmuc.com/moray

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On Mon, 24 Jan 2000 13:41:29 GMT, Lutz Kretzschmar wrote:
>Hi POV-gurus,
>
>A Moray user asked me whether it was possible to create the following
>effect:
>
>he wants to create a scene with a floor and a number of reflecting
>objects. The objects should not reflect the floor, however, they
>should only reflect each other. Is this at all possible? I pretty much
>assume it's impossible with the official 3.1, so I'm wondering whether
>MegaPOV or SuperPatch or any other patches would allow this.

What about shadows?

If you make the floor bounded_by a miniscule sphere around the camera, 
it will work for most camera angles.  If they need shadows of the spheres
on the floor as well, they'll need to bound by a union of miniscule 
spheres around the camera and each light source.

-- 
These are my opinions.  I do NOT speak for the POV-Team.
The superpatch: http://www2.fwi.com/~parkerr/superpatch/
My other stuff: http://www2.fwi.com/~parkerr/traces.html

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On 24 Jan 2000 08:56:13 -0500, Ron Parker wrote:
>If you make the floor bounded_by a miniscule sphere around the camera, 
>it will work for most camera angles.  If they need shadows of the spheres
>on the floor as well, they'll need to bound by a union of miniscule 
>spheres around the camera and each light source.

scratch that; the spheres will cast shadows on the floor without the floor
being bounded by the light sources.  The floor won't cast shadows on anything 
though.

-- 
These are my opinions.  I do NOT speak for the POV-Team.
The superpatch: http://www2.fwi.com/~parkerr/superpatch/
My other stuff: http://www2.fwi.com/~parkerr/traces.html

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It is possible with official POV, with manual bounding.
Just bound the floor with a tiny sphere near / around the camera. Now, the floor
shows up only in direct camera rays. Note that the floor would currently not
cast shadows. If you want it to cast shadows, you should add a small bounding
object near the light source(s) too.

It's easier in MegaPov, which has the no_image and no_reflection keywords. They
work the same way as no_shadow.

Margus

Lutz Kretzschmar wrote:
> 
> Hi POV-gurus,
> 
> A Moray user asked me whether it was possible to create the following
> effect:
> 
> he wants to create a scene with a floor and a number of reflecting
> objects. The objects should not reflect the floor, however, they
> should only reflect each other. Is this at all possible? I pretty much
> assume it's impossible with the official 3.1, so I'm wondering whether
> MegaPOV or SuperPatch or any other patches would allow this.
> 
> Thanks,
> 
> - Lutz
>   email : lut### [at] stmuccom
>   Web   : http://www.stmuc.com/moray

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Hi Margus Ramst, you recently wrote in povray.general:

> Just bound the floor with a tiny sphere near / around the camera. 
Ahh, neat. Thanks Ron and Margus.

- Lutz
  email : lut### [at] stmuccom
  Web   : http://www.stmuc.com/moray

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If the object to be faked is rather complex, bounding it with a sphere
around the camera will make the scene render slower since tests with the
complex object will be performed for each pixel on screen. With a plane it
doesn't matter, since the plane is tested for each pixel anyways, but for
other objects it may be significant.
  A better solution is to use a regular bounding object which is the scaled
so that it get very small and goes very near the camera (like the camera was
the origin and you scaled the object very small). This way you get both
effects, fast rendering and the desired special effect.
  The scaling can be achieved this way:

#declare camera_location = ...

object
{ VampireObject
  bounded_by
  { object
    { Whatever
      translate -camera_location
      scale .0001
      translate camera_location
    }
  }
}

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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> Lutz Kretzschmar wrote:
> >
> > Hi POV-gurus,
> >
> > A Moray user asked me whether it was possible to create the following
> > effect:
> >
> > he wants to create a scene with a floor and a number of reflecting
> > objects. The objects should not reflect the floor, however, they
> > should only reflect each other. Is this at all possible? I pretty much
> > assume it's impossible with the official 3.1, so I'm wondering whether
> > MegaPOV or SuperPatch or any other patches would allow this.

Margus Ramst <mar### [at] peakeduee> wrote in message
news:388C5B3E.1B990BFB@peak.edu.ee...
> It is possible with official POV, with manual bounding.
> Just bound the floor with a tiny sphere near / around the camera. Now, the
floor
> shows up only in direct camera rays. Note that the floor would currently
not
> cast shadows. If you want it to cast shadows, you should add a small
bounding
> object near the light source(s) too.

I'm curious. Can someone explain how this works? I was always under the
impression that the manual bounding was used to define the size of an object
and any part of the object that was outside of the bounding object was
essentially clipped. I guess this is either only partly correct or a
misinterpretation of what actually happens. I more complete explanation
would be great.

Thanks,
Darcy

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Hi Darcy Johnston, you recently wrote in povray.general:

> I'm curious. Can someone explain how this works? 
I think it's like this: when POV-Ray traces a ray from the camera
towards an object, it first checks to see whether the ray intersects
that objects' bounding box (if it has one) and only if it does does it
then actually work out where it intersects the object. So a ray from
the camera will always intersect the bounding box (and therefore the
object will be tested, too). But a reflected ray will not intersect it
and therefore that ray will not attempt to intersect the object.

- Lutz
  email : lut### [at] stmuccom
  Web   : http://www.stmuc.com/moray

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You can think of it like this:
A ray is first tested against the bounding object (manual or automatic). If the
bounding object is hit, the ray is tested against the actual object. The main
purpose of this is to speed up rendering, since it's much faster to check an
intersection with a box or sphere than with, say, a quartic. What you describe
sounds more like clipping. Bounded_by and clipped_by should not be confused,
they work quite differently.
Bounding is viewpoint dependent: for an object to be rendered, its volume does
_not_ have to be inside the bounding object. Its 2D _projection_ from the
current viewpoint has to be in the 2D projection of the bounding object.
Basically, you can think of bounded_by as working in 2D screen space, as opposed
to the 3D space of your scene.
Clipping works similarly to the difference CSG operation. But clipping leaves a
hole in the cut object where difference leaves the surface of the cutting
object. Clipping is not viewpoint dependant.

Margus

Darcy Johnston wrote:
> 
> I'm curious. Can someone explain how this works? I was always under the
> impression that the manual bounding was used to define the size of an object
> and any part of the object that was outside of the bounding object was
> essentially clipped. I guess this is either only partly correct or a
> misinterpretation of what actually happens. I more complete explanation
> would be great.
> 
> Thanks,
> Darcy

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Lutz Kretzschmar wrote:
> 
> Hi POV-gurus,
> 
> A Moray user asked me whether it was possible to create the following
> effect:
> 
> he wants to create a scene with a floor and a number of reflecting
> objects. The objects should not reflect the floor, however, they
> should only reflect each other. Is this at all possible? I pretty much
> assume it's impossible with the official 3.1, so I'm wondering whether
> MegaPOV or SuperPatch or any other patches would allow this.
> 

Have a look at the NO_REFLECTION / NO_IMAGE patch
 (seems to be in MegaPov).

 I would simply apply NO_REFLECTION to the floor object.

The main advantage is that it does not perturb the bounding tree
(And unless NO_SHADOW is also speficied, you will get a shadow for
the floor, if you have any light that make the floor cast one
 [semi-transparent floor ??])

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