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29 Mar 2024 10:02:59 EDT (-0400)
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From: Stephen
Subject: Re: The question about of projected through option
Date: 18 Dec 2017 08:17:08
Message: <5a37bfd4$1@news.povray.org>
On 18/12/2017 13:14, Stephen wrote:
> So multiply the camera position by -1 * Y and maybe give it a little 
> offset in the X or Y direction.

Oops! I use a LH co-ord system.

Should be: offset in the X or Z direction

-- 

Regards
     Stephen


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From: Alain
Subject: Re: The question about of projected through option
Date: 18 Dec 2017 18:13:03
Message: <5a384b7f$1@news.povray.org>
Le 17-12-18 à 06:42, Masaki  a écrit :
> I appreciate for your kind advice.
> 
> I started pov-ray recently, so it takes some time to understand the all advice.
> I would like to try the two way, projected through and spotlights.
> 
> The projected through puzzled me, so I have to consider.
> 
> There are two questions about using spotlight.
> (1) How can I configurate the “negative” option?

light_source{Location rgb -1}
Any negative value mean a negative light. The intensity of a light can 
have almost any value in a range of -1e12 to 1e12... And, if the light 
is not white, a component can be negative while the others are positive 
like rgb<-2, 1, 0.7>

> (2) Can the “negative” light distinguish the “positive” light completely?
> It seems that the “negative” light only weaken the positive light.

It can totally suppress a normal light. It only need to have the same or 
larger intensity.

> 
> The reason why I place the 10 lights is that I want to know the response when
> the light source moves in the depth direction, but I am very happy if the
> reasonable result is obtained from the one light at first.

In that case, it may be a good idea to use coloured lights. That way, 
you'll be better able to distinguish them.

> 
> I post again the source code with object (hexagonal prism).
> 
> ////////////////////////////////////////////////
> #include "colors.inc"
> #include "textures.inc"
> 
> background{Black}
> 
> camera {
> 
>      location <0, -3, 0>
>      right <-1.33, 0, 0>
>      angle 40
>      look_at <0, 0.5, 0>
>    }
> 
> 
> 
> //Object
> object {//you don't need that object wrapper.
>    prism {
>      linear_sweep
>      linear_spline
>      0.
>      1.
>      7.

This risk been interpreted as 0.1, 7.0
Replace those dots with comas.

>      <2,0>, <1,1.7320508>, <-1,1.7320508>, <-2,0>, <-1, -1.7320508>,
> <1,-1.7320508>, <2,0>
> 
>         hollow

Not needed unless you plan adding some media. hollow is only meant to 
allow an object to contain some media.

> 
> 
>        material {
> 
> 
>           texture {
> 
>              pigment { rgbf<1.0, 1.0, 1.0, 0.7> }
> 
>              finish {
>                 specular 1
>                 roughness 0.001
>                 ambient 0
>                 diffuse 0
> 
>                 reflection {
>                    0.1
>                    fresnel on
>                 }
> 
>                 conserve_energy
>              }
> 
>           }
> 
>        }
> 
>        interior {
>           ior 1.458
>           fade_distance 1.0
>           fade_power 2
>        }
>      }
> }

For a material, you should use fade_power 1 or fade_power 1001 to get a 
more realistic result.
fade_power 2 is for light attenuation over a distance in empty space.

If you want the light trajectory to show in that object, you need to 
fill it with some scattering media. As it is now, the light can only 
show at the surface. It's made impossible by the diffuse 0, meaning that 
the surface don't diffuse any of the incoming light.

> 
>   //Source
>   #declare r2 = seed(12345);
>   #declare I = 0;
>   #declare Number = 10;
> 
> 
> 
>   #while (I < Number)
> 
>   #declare A = rand(r2);
> 
>   #declare Object1 = torus {
>                              0.1, 0.05
>                              sturm
>                              translate <0, A-0.1, 0>
> 
>   }

You should make your torus much thinner. As it is now, the illuminated 
areas from the various lights overlap a lot unless you are very close to 
the torus.

#declare Object1 = torus{0.1, 0.002 translate <0, -0.1, 0>}

> 
> 
> 
> 
> 
>   light_source {
> 
>          <0, A, 0>
>          color
	rgb<rand(r2),rand(r2),rand(r2)>
Makes your lights multi-coloured

>          projected_through {Object1}
> 
>          }
> 
> 
> 
> #declare I = I+1;
> #end
> /////////////////////////////////////////////////////////////////
> 
> Regards,
> 
> Masaki
> 
> 
>


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From: Alain
Subject: Re: The question about of projected through option
Date: 18 Dec 2017 18:19:45
Message: <5a384d11@news.povray.org>
Le 17-12-17 à 13:36, Kenneth a écrit :
> clipka <ano### [at] anonymousorg> wrote:
> 
>>
>> To limit the light to, say, between 40 to 50 degrees, you could create a
>> spotlight with a 50 degree angle, and another spotlight with a 40 degree
>> angle and /negative/ brightness.
>>
> 
> That's an interesting concept: 'negative' light, to subtract from another light.
> Such an idea never occured to me, one worth checking out; thanks.
> 
> 
> 
There is at least one sample scene that use a negative light. Look at 
crater_dat.pov in /scenes/advanced/crater


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From: Stephen
Subject: Re: The question about of projected through option
Date: 18 Dec 2017 21:45:20
Message: <5a387d40$1@news.povray.org>
On 17/12/2017 18:36, Kenneth wrote:
> clipka <ano### [at] anonymousorg> wrote:
> 
>>
>> To limit the light to, say, between 40 to 50 degrees, you could create a
>> spotlight with a 50 degree angle, and another spotlight with a 40 degree
>> angle and /negative/ brightness.
>>
> 
> That's an interesting concept: 'negative' light, to subtract from another light.
> Such an idea never occured to me, one worth checking out; thanks.
> 
> 
> 
I made an animation of a negative spotlight sweeping over the Stamford 
bunny a while ago. Slightly unsettling.
I posted an example in p.b.i

-- 

Regards
     Stephen


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From: Masaki 
Subject: Re: The question about of projected through option
Date: 18 Dec 2017 22:15:01
Message: <web.5a38834151d01bcd2a06f29c0@news.povray.org>
Thanks for the reply.
I have some new questions.

> There are a couple of things wrong with your scene. First, your lights
> and objects are inside the Prism. So you will not see anything.
(1) Does it mean that I can not see the light from the outside of the prism when
there is a light source in the prism which is transparent object?


(2) In pov-ray, is it possible for the camera to visualize the direct light from
the source?
I want to acquire the conical surface light through the prism object directly.

Regards
        Masaki


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From: Stephen
Subject: Re: The question about of projected through option
Date: 19 Dec 2017 07:12:06
Message: <5a390216$1@news.povray.org>
On 19/12/2017 03:12, Masaki  wrote:
> Thanks for the reply.
> I have some new questions.
> 
>> There are a couple of things wrong with your scene. First, your lights
>> and objects are inside the Prism. So you will not see anything.
> (1) Does it mean that I can not see the light from the outside of the prism when
> there is a light source in the prism which is transparent object?
> 
> 
If the object is transparent or filtered then the light will shine 
through. By the amount of transparency or filter value.

> (2) In pov-ray, is it possible for the camera to visualize the direct light from
> the source?

In the camera use Point_at and point your camera at the light's location.


> I want to acquire the conical surface light through the prism object directly.
> 
> Regards
>          Masaki
> 
> 
> 
> 


-- 

Regards
     Stephen


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From: Alain
Subject: Re: The question about of projected through option
Date: 19 Dec 2017 16:36:57
Message: <5a398679@news.povray.org>
Le 17-12-18 à 22:12, Masaki  a écrit :
> Thanks for the reply.
> I have some new questions.
> 
>> There are a couple of things wrong with your scene. First, your lights
>> and objects are inside the Prism. So you will not see anything.
> (1) Does it mean that I can not see the light from the outside of the prism when
> there is a light source in the prism which is transparent object?

I think that he miss the transparency.
As your prism is transparent, light will shine through.

> 
> 
> (2) In pov-ray, is it possible for the camera to visualize the direct light from
> the source?

Never ever.
The light_source is an abstraction that have no tangible existence. It 
just illuminate things. For a light_source to be visible, you need to 
associate it with some object, usually by the use of looks_like{...}
It can also be achieved using an union that include the light.
Also, the camera can absolutely never ever directly see the photons if 
you use them. They can only be seen when they hit a surface or are 
deposited into some scattering media.

> I want to acquire the conical surface light through the prism object directly.

For that, you need to fill that prism with some scattering media.
interior{
	media{ ...media descriptor... }
  }
Please refer to the documentation about media, especially the scattering 
media.

> 
> Regards
>          Masaki
> 
> 
> 
>


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From: Alain
Subject: Re: The question about of projected through option
Date: 19 Dec 2017 16:38:26
Message: <5a3986d2$1@news.povray.org>
Le 17-12-19 à 07:12, Stephen a écrit :
> On 19/12/2017 03:12, Masaki  wrote:
>> Thanks for the reply.
>> I have some new questions.
>>
>>> There are a couple of things wrong with your scene. First, your lights
>>> and objects are inside the Prism. So you will not see anything.
>> (1) Does it mean that I can not see the light from the outside of the 
>> prism when
>> there is a light source in the prism which is transparent object?
>>
>>
> If the object is transparent or filtered then the light will shine 
> through. By the amount of transparency or filter value.
> 
>> (2) In pov-ray, is it possible for the camera to visualize the direct 
>> light from
>> the source?
> 
> In the camera use Point_at and point your camera at the light's location.

The light source will still not show.

> 
> 
>> I want to acquire the conical surface light through the prism object 
>> directly.
>>
>> Regards
>>          Masaki
>>
>>
>>
>>
> 
>


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From: Stephen
Subject: Re: The question about of projected through option
Date: 19 Dec 2017 17:38:03
Message: <5a3994cb$1@news.povray.org>
On 19/12/2017 21:38, Alain wrote:
> Le 17-12-18 à 22:12, Masaki  a écrit :
>> Thanks for the reply.
>> I have some new questions.
>>
>>> There are a couple of things wrong with your scene. First, your lights
>>> and objects are inside the Prism. So you will not see anything.
>> (1) Does it mean that I can not see the light from the outside of the 
>> prism when
>> there is a light source in the prism which is transparent object?
> 
> I think that he miss the transparency.

I did.


> As your prism is transparent, light will shine through.
> 
>>
>>
>> (2) In pov-ray, is it possible for the camera to visualize the direct 
>> light from
>> the source?
> 
> Never ever.
> The light_source is an abstraction that have no tangible existence. It 
> just illuminate things. For a light_source to be visible, you need to 
> associate it with some object, usually by the use of looks_like{...}
> It can also be achieved using an union that include the light.

There is always the "Looks_like" in the camera statement.



-- 

Regards
     Stephen


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From: Bald Eagle
Subject: Re: The question about of projected through option
Date: 19 Dec 2017 20:15:00
Message: <web.5a39b90951d01bcd5cafe28e0@news.povray.org>
"Masaki " <mas### [at] akanewasedajp> wrote:

> (2) In pov-ray, is it possible for the camera to visualize the direct light from
> the source?
> I want to acquire the conical surface light through the prism object directly.

By "acquire", do you mean visualize?

One thing to remember about POV-Ray, is that it's only a mathematical construct
- a simulation a light and its interaction with objects.  It can do that REALLY
well, so it's easy to forget, but none of it really "exists" until it gets
rendered as a pixel of a specific color and brightness.

Light, in POV-Ray is much like real light, in that you can't really see it
unless it interacts with something else.  You can't see the wind itself, but you
can see its effect on things it interacts with.

You could add a cloud of media for the light to light up.

Other than that, I'd say that depending upon what you want to see as the end
result, then you might try modeling a sort of container for the light cone.

Sometimes when I'm writing a scene, I make a fake model of the light source, and
draw a cylinder from that to my look_at point, and draw a transparent cone if
it's a spotlight.

Similarly, two extremely thin nested cones with transparency might give you a
usable effect.
You might consider defining a CSG container that demarcates the boundaries of
your light, and fill it randomly with VERY small spheres (or blobs) - so thin
that they may or may not be a pixel wide, or draw VERY thin cylinders so that
you get the same random visibility along their length.

Just some ideas.


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