Is it possible to simulate a projected image using photons and radiosity?

My basic scene setup is as follows:

C = Cylinder (Object (ideally) projected)
L = Lens (A curved peice of glass)
B = White box ('Screen')
P = Light Source

                                        PP
                                        PP


CC                                      BB
CC                    LL                BB
CC                    LL                BB
CC                    LL                BB

So far, no luck.

Scene source follows.

global_settings{
        photons{
                count 50000
                        autostop 0
                        jitter .4
        }
        radiosity{
        pretrace_start 0.08
                pretrace_end   0.04
                count 35

                nearest_count 5
                error_bound 1.8
                recursion_limit 3

                low_error_factor 0.5
                gray_threshold 0.0
                minimum_reuse 0.015
                brightness 1

                adc_bailout 0.01/2
        }
                max_trace_level 20

}
camera{
        location <10,10,-30>
        look_at <0,10,-10>
}

cylinder{<0,0,-40>,<0,20,-40>,3 pigment{rgb <0,1,0>}
photons{
        reflection on
}
}

light_source{<0,100,50>,1
photons{
        refraction on
        reflection on
}
}
box{<-50,0,-50>,<50,-1,50> pigment{rgb .2}
photons {collect on}
}
cylinder{

        <0,5,0>,<0,15,0>,5
        scale <1,1,.25>
texture{
                pigment{
                        rgbf <1,1,1,.97>
                }
        }
        interior{
                ior 1.2
        }
                
        
        translate <0,0,-10>
        photons{
                target
                refraction on
                reflection on
                collect off
        }
}
box{<10,0,10>,<-10,20,11> texture{pigment{rgb 1}} photons{collect on}}
CC                                      BB

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In article <3eb000fd@news.povray.org>, Tyler Eaves <tyl### [at] cg1org> 
wrote:

> Is it possible to simulate a projected image using photons and radiosity?

Basically, you want to use a lens to focus light reflected from a scene 
onto a screen? This is possible in theory, but would be very, very slow. 
There's a reason raytracers like POV-Ray primarily follow light 
backwards from the camera.
Photons and radiosity do simulate light travelling through the scene, 
but the current implementation of photons doesn't simulate diffuse 
scattering and you would need insane radiosity settings to get more than 
a blurry glow. This is just not the type of thing you want to simulate 
fully, your best bet is to do some kind of mock-up. You could render a 
view of the scene from what the "camera" would see and use that on a 
transparent image map with light shining through it onto the screen, 
perhaps using projected_through to get the lighting set up right. In 
MegaPOV, I think you could skip the first render stage and use a camera 
pigment for the projection filter.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Christopher James Huff wrote:

> In article <3eb000fd@news.povray.org>, Tyler Eaves <tyl### [at] cg1org>
> wrote:
> 
>> Is it possible to simulate a projected image using photons and radiosity?
> 
> Basically, you want to use a lens to focus light reflected from a scene
> onto a screen? This is possible in theory, but would be very, very slow.
> There's a reason raytracers like POV-Ray primarily follow light
> backwards from the camera.
> Photons and radiosity do simulate light travelling through the scene,
> but the current implementation of photons doesn't simulate diffuse
> scattering and you would need insane radiosity settings to get more than
> a blurry glow. This is just not the type of thing you want to simulate
> fully, your best bet is to do some kind of mock-up. You could render a
> view of the scene from what the "camera" would see and use that on a
> transparent image map with light shining through it onto the screen,
> perhaps using projected_through to get the lighting set up right. In
> MegaPOV, I think you could skip the first render stage and use a camera
> pigment for the projection filter.
> 

Okay, darn. I wasn't interested in the "effect" so much as the modeling.
I've been learning some basic optics in my physics class, and wanted to see
if I could model some of it in pov.

Post a reply to this message

Tyler Eaves wrote:
>
>Okay, darn. I wasn't interested in the "effect" so much as the modeling.
>I've been learning some basic optics in my physics class, and wanted to see
>if I could model some of it in pov.
>

You might be better off modelling a telescope or microscope.  Use focal
blur, that "simulates" your eye.  If the image is blurry, your focal
lengths are off.

I've done it myself, rendering a 4.5 inch reflector telescope, with a 910mm
focal length primary mirror with a diameter of 114mm, and a small 45 degree
inclined secondary mirror, and then I created a 25mm focal length
refracting lens.  Turned on focal blur, and adjusted the position of the
objective lens until I got it to focus.  It was a very satisfying project,
though it took forever to test each rendering.

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"Tyler Eaves" <tyl### [at] cg1org> wrote in message
news:3eb000fd@news.povray.org...
> Is it possible to simulate a projected image using photons and radiosity?
>
I've been able to create a slide projection using photons (not radiosity),
but with strange results.
There are curious artifacts in the projected image.

http://images.walkington.net

Alan

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