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28 Mar 2024 09:34:55 EDT (-0400)
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From: andy Wang
Subject: Ask a question about transmission
Date: 1 Jun 2008 23:10:00
Message: <web.484363b26a6f8b3135072ccd0@news.povray.org>
Sorry for my poor english!

The Last message not clearly, so I described my problem again.

In my study, the result images have been divided into four parts, namely, bright
objects, shaded objects, bright background and shaded background. source
light's azimuth and zenith angle be fixed,When the camera to change the azimuth
and zenith angle,  the four components will be changed.

The interaction of light and objects, including reflection and transmission.In
my study ,When the light through objects, Divided into two cases :1
through a layer object, objects should be bright ;2 through two or more
layers objects are shaded. But now,pov-ray can not distinguish between the two
cases. I have tried 'filter' and 'tansmit' , but the results unsatisfactory.
How to solve this problem?

Thanks a lot!


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From: Chris B
Subject: Re: Ask a question about transmission
Date: 2 Jun 2008 06:06:10
Message: <4843c612$1@news.povray.org>
"andy Wang" <wjg### [at] yahoocomcn> wrote in message 
news:web.484363b26a6f8b3135072ccd0@news.povray.org...
>
> Sorry for my poor english!
>
> The Last message not clearly, so I described my problem again.
>
> In my study, the result images have been divided into four parts, namely, 
> bright
> objects, shaded objects, bright background and shaded background. source
> light's azimuth and zenith angle be fixed,When the camera to change the 
> azimuth
> and zenith angle,  the four components will be changed.
>
> The interaction of light and objects, including reflection and 
> transmission.In
> my study ,When the light through objects, Divided into two cases :1
> through a layer object, objects should be bright ;2 through two or more
> layers objects are shaded. But now,pov-ray can not distinguish between the 
> two
> cases. I have tried 'filter' and 'tansmit' , but the results 
> unsatisfactory.
> How to solve this problem?
>
> Thanks a lot!
>

Hi Andy,
The question is still not totally clear, but you show good persistence :-).

A couple of things that you may like to clarify:
o  Where you refer to 'planes' in your original post, are these POV-Ray 
planes (with a single infinite surface) or are they more like sheets of 
glass with two surfaces?
o  You show planes b and c being side-by-side, which, if they overlap, may 
be giving you problems with concurrent surfaces.
o  Your diagram shows the light shining straight into the camera, which will 
not work very well.

What I suspect you want is to have a bright object or a bright background 
that can be filtered by the 'planes' (see the example code below), then you 
will actually 'see' the light coming off that bright object.

I'm not sure if either of these is the question you're asking, but ...

a) If you want to block out all light shining through more than one object 
you could set the max_trace_level to be quite small (e.g. 3). Light arriving 
at the camera that has passed through too many surfaces will then be 
completely blocked and the pixel will appear black.

b) If you want to progressively reduce the amount of light getting through 
to the camera, based on how many objects the light has passed through, then 
you may need to increase max_trace_level (maybe try 10) and set a relatively 
high transmit value on each object. For example using a transmit value of 
0.9 would cut out just 10% of the light as it passes through each surface. 
Light passing through 4 surfaces would therefore be 60% as bright as light 
that hadn't passed through any.

Otherwise you may wish to post a small snippet of code that illustrates your 
problem.
Here's a small but complete scene that may help you to express your problem:

camera {location <0,0,-1> look_at 0}
//global_settings { max_trace_level 3 }

// A Bright object
sphere {<0,0,3>,1
  pigment {rgb <1,1,0>}
  finish  {ambient 1}
}

// Top left quadrant
box {<0,0,0>,<-1,1,0.01>
  pigment {rgbt <1,1,1,0.9>}
}
// Bottom left quadrant
box {<0,0,0>,<-1,-1,0.01>
  pigment {rgbt <1,1,1,0.9>}
  finish {ambient 0}
}
// Bottom left quadrant (further away)
box {<0,0,0>,<-1,-1,0.01>
  translate z*0.02
  pigment {rgbt <1,1,1,0.9>}
  finish {ambient 0}
}
// Bottom right quadrant
box {<0,0,0>,<1,-1,0.01>
  translate z*0.02
  pigment {rgbf <1,0,0,1>}
  finish {ambient 0}
}

Note that there is no light source in this scene, just a sphere with ambient 
set to '1'. The bottom left quadrant is masked by two boxes, so appears 
dimmer than the top left quadrant which is only masked by one. The bottom 
right quadrant is masked by a red filter.

If you uncomment the max_trace_level setting you should see the bottom left 
quadrant turn black, because light from the sphere would need to trace 5 
tracks to pass through the 4 surfaces to get to the camera.

Regards,
Chris B.


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From: andy Wang
Subject: Re: Ask a question about transmission
Date: 3 Jun 2008 11:50:00
Message: <web.484566374db172e9bfc96970@news.povray.org>
thanks for your help!


The problem has been resolved.Just add 'double_illuminate' to the object.
:)


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