POV-Ray : Newsgroups : povray.newusers : angle of incidence of rays of light Server Time: 16 Dec 2018 21:38:18 GMT
  angle of incidence of rays of light (Message 1 to 7 of 7)  
From: ttyUSB0
Subject: angle of incidence of rays of light
Date: 23 Sep 2018 13:25:01
Message: <web.5ba79315ca7dd69ce66e1eb00@news.povray.org>
I have a material that creates a shadow of varying density, depending on the
angle to the direction of the light rays.
Is it possible to specify a variable transmission of light through the surface,
depending on the angle of light rays incidence?


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From: Jim Holsenback
Subject: Re: angle of incidence of rays of light
Date: 23 Sep 2018 14:18:59
Message: <5ba7a0d3$1@news.povray.org>
On 9/23/18 9:20 AM, ttyUSB0 wrote:
> I have a material that creates a shadow of varying density, depending on the
> angle to the direction of the light rays.
> Is it possible to specify a variable transmission of light through the surface,
> depending on the angle of light rays incidence?
> 
> 

sure povray does that ... check out ior to characterize the interior of 
your material. have a look in the docs Reference->Scene File 
Extras->Include Files you'll see ior mentioned in a couple of places. 
look in glass.inc and you'll see how to put together a material 
definition. transmit and filter in pigment is worth looking at...povray 
has subsurface light transport too


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From: Jim Holsenback
Subject: Re: angle of incidence of rays of light
Date: 23 Sep 2018 14:24:46
Message: <5ba7a22e$1@news.povray.org>
On 9/23/18 10:18 AM, Jim Holsenback wrote:
> On 9/23/18 9:20 AM, ttyUSB0 wrote:
>> I have a material that creates a shadow of varying density, depending 
>> on the
>> angle to the direction of the light rays.
>> Is it possible to specify a variable transmission of light through the 
>> surface,
>> depending on the angle of light rays incidence?
>>
>>
> 
> sure povray does that ... check out ior to characterize the interior of 
> your material. have a look in the docs Reference->Scene File 
> Extras->Include Files you'll see ior mentioned in a couple of places. 
> look in glass.inc and you'll see how to put together a material 
> definition. transmit and filter in pigment is worth looking at...povray 
> has subsurface light transport too

oh objects can also have interior media too...start at 
Reference->Special Effects->Media


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From: clipka
Subject: Re: angle of incidence of rays of light
Date: 23 Sep 2018 15:44:49
Message: <5ba7b4f1$1@news.povray.org>
Am 23.09.2018 um 15:20 schrieb ttyUSB0:
> I have a material that creates a shadow of varying density, depending on the
> angle to the direction of the light rays.
> Is it possible to specify a variable transmission of light through the surface,
> depending on the angle of light rays incidence?

That's actually normal behaviour for pretty much all transparent
real-life materials; usually, the difference in shadow is due to
specular reflection at the surfaces that "steals" part of the light; in
real life, specular reflection is stronger at shallow angles, as
expressed by Fresnel's law.


As Jim already hinted at, POV-Ray can take into account Fresnel's law
for /some/ effects, if you specify an index of refraction.

However, it doesn't normally do so for shadows; to make POV-Ray do so,
you have to:

- Specify the object's refractive index (via `ior` in an `interior` block).

- Set up the material to respect fresnel's law for reflection (using
`reflection { fresnel on }` in a finish block).

- Set up the material to account for reflected light in computing
transmission (using `conserve_energy` in a finish block).

- Use photon mapping to coax POV-Ray into actually computing advanced
transmission effects for shadows.


An alternative is to use the `aoi` (angle of incidence) pattern for the
pigment, varying the `trans` component of the colour according to the angle.


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From: ttyUSB0
Subject: Re: angle of incidence of rays of light
Date: 28 Sep 2018 07:20:00
Message: <web.5badd56347fdf4edb540a4420@news.povray.org>
Thank you, clipka and Jim.
I want to model not a three-dimensional, but a flat object. Like polygon, or
mesh/mesh2.

Directive
pigment{aoi}
works well, surface color depends of angle of incidence, but shadow is always
the same.
I cant found, how to make my surface cast semi-transparent shadows.

Keywords 'transmit' and 'filter' works only with 'color'. How to make texture
transparent?


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From: ttyUSB0
Subject: Re: angle of incidence of rays of light
Date: 28 Sep 2018 08:00:01
Message: <web.5badde7747fdf4edb540a4420@news.povray.org>
"ttyUSB0" <nomail@nomail> wrote:
I have read the manual carefully.. :)
This code does something similar to what I need:

polygon {4, <-w/2, -h/2>, <w/2, -h/2>, <w/2, h/2>, <-w/2, h/2>
    pigment{
        aoi
        color_map {
            [0.71 color Blue transmit 0.1]
            [0.99 color Red transmit 0.9]
        }
    }
    rotate 15*x
    no_image
}

Shadow now depends on rotation angle.


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From: Alain
Subject: Re: angle of incidence of rays of light
Date: 29 Sep 2018 16:34:51
Message: <5bafa9ab$1@news.povray.org>
Le 18-09-28 à 03:16, ttyUSB0 a écrit :
> Thank you, clipka and Jim.
> I want to model not a three-dimensional, but a flat object. Like polygon, or
> mesh/mesh2.
> 
> Directive
> pigment{aoi}
> works well, surface color depends of angle of incidence, but shadow is always
> the same.
> I cant found, how to make my surface cast semi-transparent shadows.
> 
> Keywords 'transmit' and 'filter' works only with 'color'. How to make texture
> transparent?
> 
> 

You can add «transmit Value» or «filter Value» after the pigment.
You can also use rgbt, rgbf or rgbft to definne your pigment :
rgb<R, G, B>
rgbt<R, G, B, Transmit>
rgbf<R, G, B, Filter>
rgbft<R, G, B, Filter, Transmit>

When using filter and transmit, always make sure that (filter + 
transmit) <= 1

The «color» or «colour» keyword is always optional unless you use this 
obsolete construction :
colour red RedValue green GreenValue blue BlueValue


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