Food for thought:

 Ok we know that a sky sphere is a virtual effect and that for all intensive
purposes it is not a real object. On the same token it is not really a pigment
either because it cannot be applied to an object. This leave us with the
following observations that seem somewhat undefined as far as it's usage
(at least from the simple description in the docs)...


Attempting to render the following produces an error from Pov stating that
there are no objects in the scene...

--
camera{location z*-5 look_at 0}
sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}
--

So it is not an object is it ?



Rendering the following with the addition of a box allows the render to
go without error because of the addition of an object to the scene...

--
camera{location z*-5 look_at 0}
box{-.1,.1 pigment{rgb 1}}
sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}
--

So it is an object only when there is a real object in the scene ?
What if I only want to raytrace a sky_sphere for a background image ?




The next little ambiguity that we can try is the following...

--
camera{location z*-5 look_at 0}
box{-.1,.1 pigment{rgb 1}}

#declare Sky =
sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}

object{Sky}
--

Whoops ! Now we get an error that an object is expected but a sky_sphere is
found instead. Now we know for sure that Pov does not recongnize it as an
object.



So we change things around again to accomodate the parser and try the
following code...

--
camera{location z*-5 look_at 0}
box{-.1,.1 pigment{rgb 1}}

#declare Sky =
sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}

sky_sphere{Sky}
--

Well that does work but the question is WHY ? Because a sky_sphere is a sky_sphere
is a sky_sphere ! 


Which leaves us with the still unanswered question: What is a sky_sphere ?


Enjoy your meal,

-- 
Ken Tyler

See my 850+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

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Ken wrote:
> 
> Food for thought:
> 
...
>
> Which leaves us with the still unanswered question: What is a sky_sphere ?
> 
> Enjoy your meal, 

(Dominee Gremdaat?)

> 
> --
> Ken Tyler
> 

Perhaps the same goes for background.
Anyway, your dealing here with the metaphysics of POV.
Another interesting question might be: what's BEHIND a sky_sphere (or a
background).
Not a galaxy-include...

Dominee Remdaat

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Ken <tyl### [at] pacbellnet> schreef in berichtnieuws
> Attempting to render the following produces an error from Pov stating
that there are no objects in the scene...
>
> --
> camera{location z*-5 look_at 0}
> sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}
> --

And adding a lightsource to this small scene makes POV-Ray crash :(

Ingo

Post a reply to this message

ingo wrote:
> 
> Ken <tyl### [at] pacbellnet> schreef in berichtnieuws
> > Attempting to render the following produces an error from Pov stating
> that there are no objects in the scene...
> >
> > --
> > camera{location z*-5 look_at 0}
> > sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}
> > --
> 
> And adding a lightsource to this small scene makes POV-Ray crash :(
> 
> Ingo

Can you provide an example so that I can confirm it ?

-- 
Ken Tyler

See my 850+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

Post a reply to this message

Ken <tyl### [at] pacbellnet> schreef in berichtnieuws > Can you provide an
example so that I can confirm it ?

camera{location z*-5 look_at 0}
sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}
light_source {<500,500,-500> rgb 1}


PII 233, NT4 SP4, POV3.1g msvc

Ingo

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ingo wrote:
> 
> Ken <tyl### [at] pacbellnet> schreef in berichtnieuws > Can you provide an
> example so that I can confirm it ?
> 
> camera{location z*-5 look_at 0}
> sky_sphere{pigment{gradient y pigment_map{[0 blue 1][1 red 1]}}}
> light_source {<500,500,-500> rgb 1}
> 
> PII 233, NT4 SP4, POV3.1g msvc
> 
> Ingo

It does not crash on my system

P200 mmx, Win 98, Pov3.1g.watcom

-- 
Ken Tyler

See my 850+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

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Doesn't the usual concept of a 'sky_sphere' make it a background
pigment? Same as 'background' yet capable of color_map inclusion? So,
if you can figure background out you will have your answer perhaps 8-0
that all points not occupied by a object, and behind every object,
there is the sky sphere. Not a entity per se, moreso a environment.

Bob

Remco de Korte <rem### [at] xs4allnl> wrote in message
news:37C7DD9D.FD641BC8@xs4all.nl...
> Ken wrote:
> >
> > Food for thought:
> >
> ...
> >
> > Which leaves us with the still unanswered question: What is a
sky_sphere ?
> >
> > Enjoy your meal,
>
> (Dominee Gremdaat?)
>
> >
> > --
> > Ken Tyler
> >
>
> Perhaps the same goes for background.
> Anyway, your dealing here with the metaphysics of POV.
> Another interesting question might be: what's BEHIND a sky_sphere
(or a
> background).
> Not a galaxy-include...
>
> Dominee Remdaat
>

Post a reply to this message

Ken wrote:
> 
> Which leaves us with the still unanswered question: What is a
> sky_sphere ?

The sky_sphere is simply a way of adding a layer to the background.

According to the docs, you can legally define both a sky_sphere and
a background, and where the sky_sphere is transparent, the background
will show through.

The docs list the sky_sphere under atmoshperic effects, and not objects.

Regards,
John
-- 
ICQ: 46085459

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Remco de Korte <rem### [at] xs4allnl> wrote:
: Another interesting question might be: what's BEHIND a sky_sphere (or a
: background).

  That certainly is an interesting question. Perhaps if you move the
camera very very very very far away from the origin, you will reach the
border of the sky_sphere...

-- 
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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Nieminen Juha wrote:
> 
> Remco de Korte <rem### [at] xs4allnl> wrote:
> : Another interesting question might be: what's BEHIND a sky_sphere (or a
> : background).
> 
>   That certainly is an interesting question. Perhaps if you move the
> camera very very very very far away from the origin, you will reach the
> border of the sky_sphere...

That's no good because then you would fall off the edge of the world. Duh !

-- 
Ken Tyler

See my 850+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

Post a reply to this message