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23 Dec 2024 18:09:46 EST (-0500)
  Faking "curvedness" (Message 1 to 10 of 10)  
From: SharkD
Subject: Faking "curvedness"
Date: 26 Aug 2009 19:50:42
Message: <4a95ca52$1@news.povray.org>
Due to the size differences involved, it's not practical (AFAIK) to 
model the curvature of the Earth in scenes with objects as small as a 
person. However, I was theorizing that it might be possible to fake the 
curvature by surrounding the scene (a few thousands of meters) with a 
"lens" of a precise shape. I was wondering, is this actually feasible? 
If so, what shape of a lens should I use? How will this affect rendering 
time?

-Mike


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From: nemesis
Subject: Re: Faking "curvedness"
Date: 26 Aug 2009 20:45:00
Message: <web.4a95d6f2e4e9fe619bdbc18c0@news.povray.org>
SharkD <mik### [at] gmailcom> wrote:
> Due to the size differences involved, it's not practical (AFAIK) to
> model the curvature of the Earth in scenes with objects as small as a
> person. However, I was theorizing that it might be possible to fake the
> curvature by surrounding the scene (a few thousands of meters) with a
> "lens" of a precise shape. I was wondering, is this actually feasible?
> If so, what shape of a lens should I use? How will this affect rendering
> time?

Tek's amazing winning entry for the IRTC oct 1995 competition comes to mind:

http://exether.free.fr/irtc/index.php?sub=pg2005&lang=en&year=2005&month=10&typ=S

You could also use a convex mirror and look at the scene through it.

http://www.rennicks.com/userimgs/1121882016.47483675.phpbz2stI.jpg


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From: Warp
Subject: Re: Faking "curvedness"
Date: 27 Aug 2009 08:34:34
Message: <4a967d5a@news.povray.org>
nemesis <nam### [at] gmailcom> wrote:
> You could also use a convex mirror and look at the scene through it.

> http://www.rennicks.com/userimgs/1121882016.47483675.phpbz2stI.jpg

  Or you could simply check the camera documentation to see what different
types of camera povray offers.

-- 
                                                          - Warp


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From: SharkD
Subject: Re: Faking "curvedness"
Date: 27 Aug 2009 11:34:47
Message: <4a96a797$1@news.povray.org>
Warp wrote:
> nemesis <nam### [at] gmailcom> wrote:
>> You could also use a convex mirror and look at the scene through it.
> 
>> http://www.rennicks.com/userimgs/1121882016.47483675.phpbz2stI.jpg
> 
>   Or you could simply check the camera documentation to see what different
> types of camera povray offers.
> 

Note that I am not trying to curve the entire scene, just the distant 
objects. Using a different camera won't work.


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From: Alain
Subject: Re: Faking "curvedness"
Date: 27 Aug 2009 19:36:14
Message: <4a97186e$1@news.povray.org>
SharkD a écrit :
> Warp wrote:
>> nemesis <nam### [at] gmailcom> wrote:
>>> You could also use a convex mirror and look at the scene through it.
>>
>>> http://www.rennicks.com/userimgs/1121882016.47483675.phpbz2stI.jpg
>>
>>   Or you could simply check the camera documentation to see what 
>> different
>> types of camera povray offers.
>>
> 
> Note that I am not trying to curve the entire scene, just the distant 
> objects. Using a different camera won't work.
> 
In that case, a lense or a mirror will have the same problem.

You can always use a very large, possibly flattened in the Y direction, 
sphere as your ground. Then, you use the trace() function to get the 
normal and orient the objects relative to the surface of that sphere.


Alain


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From: Mike Williams
Subject: Re: Faking "curvedness"
Date: 27 Aug 2009 19:54:48
Message: <Yrl8jbFpyxlKFwqm@econym.demon.co.uk>
Wasn't it SharkD who wrote:
>Warp wrote:
>> nemesis <nam### [at] gmailcom> wrote:
>>> You could also use a convex mirror and look at the scene through it.
>>
>>> http://www.rennicks.com/userimgs/1121882016.47483675.phpbz2stI.jpg
>>    Or you could simply check the camera documentation to see what 
>>different
>> types of camera povray offers.
>>
>
>Note that I am not trying to curve the entire scene, just the distant 
>objects.

Unlike the real world, you can select which objects are reflected in 
PovRay mirrors. You could specify no_reflection for nearby objects and 
no_image for distant objects which you want to reflect in the curved 
mirror. Position them accordingly.

-- 
Mike Williams
Gentleman of Leisure


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From: SharkD
Subject: Re: Faking "curvedness"
Date: 28 Aug 2009 00:29:22
Message: <4a975d22$1@news.povray.org>
Mike Williams wrote:
> Unlike the real world, you can select which objects are reflected in 
> PovRay mirrors. You could specify no_reflection for nearby objects and 
> no_image for distant objects which you want to reflect in the curved 
> mirror. Position them accordingly.
> 

I was thinking of using a giant toroidal lens around the entire scene. 
Nearby objects would lie inside the torus and would not be refracted. 
Distant objects would lie outside the torus and would be refracted. Not 
sure what exact shape the lens should be. My optics is a bit rusty from 
high school...

A mirror instead of a lens might work and might even render faster, but 
I'd have to make sure most of my scene is not reflected. I would want 
the clouds to appear in the mirror, and the mirroring would probably be 
noticeable at the edge.

-Mike


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From: Mike Williams
Subject: Re: Faking "curvedness"
Date: 28 Aug 2009 21:12:11
Message: <qIFArDBkGDmKFwXV@econym.demon.co.uk>
Wasn't it SharkD who wrote:
>I was thinking of using a giant toroidal lens around the entire scene. 
>Nearby objects would lie inside the torus and would not be refracted. 
>Distant objects would lie outside the torus and would be refracted. Not 
>sure what exact shape the lens should be. My optics is a bit rusty from 
>high school...

It might be worth trying placing the camera and nearby objects inside a 
spherical lens, and giving that lens an IOR less than 1.0.

-- 
Mike Williams
Gentleman of Leisure


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From: SharkD
Subject: Re: Faking "curvedness"
Date: 28 Aug 2009 21:53:04
Message: <4a988a00$1@news.povray.org>
Mike Williams wrote:
> It might be worth trying placing the camera and nearby objects inside a 
> spherical lens, and giving that lens an IOR less than 1.0.

Even simpler! I assume I should place the sphere slightly above the 
horizon so that the rest of the scene will bend downwards?

-Mike


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From: Christian Froeschlin
Subject: Re: Faking "curvedness"
Date: 7 Sep 2009 17:30:03
Message: <4aa57b5b@news.povray.org>
SharkD wrote:

> Due to the size differences involved, it's not practical (AFAIK) to 
> model the curvature of the Earth in scenes with objects as small as a 
> person.

To fake this, you can use a different scale for your background
objects, if you also scale their distances accordingly.


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