I've just started playing around with photons  (using POV3.5 Windows)

I'm getting unexpected results when using cylinder lights and photons,
I have 3 cylinder lights (red, green and blue) pointing at a
reflective box, the light 'beams' stike the box at a 45 degree and and
reflect onto another (non-reflective) box.

I would expect to get 3 distinct light patches on the non-refective
box. Instead they seem to converge on one area.

If I replace the lights with spot lights, I get the results that I
would expect.

I'm not sure if this is a bug, or a booboo on my part.


Below is the scene text that I used

// begin scene code

global_settings
{
	photons { spacing 0.005 }
}

// reflected lights

// when using spots, the results are what I expect,
//    3 distinct lit areas on the left
// when using cylinder, photons from all three
//     lights accumulate at one area

#macro spot_or_cylinder()
//	spotlight radius 1 falloff 1
	cylinder radius 0.05 falloff 0.05 
#end

light_source
{
	<0.5, 0.25, -3>
	color blue 1
	spot_or_cylinder()
	point_at <0.5, 0.25, 0>
	photons { reflection on }
}

light_source
{
	<0.5, 0.5, -3>
	color green 1
	spot_or_cylinder()
	point_at <0.5, 0.5, 0>
	photons { reflection on }
}

light_source
{
	<0.5, 0.75, -3>
	color red 1
	spot_or_cylinder()
	point_at <0.5, 0.75, 0>
	photons { reflection on }
}


// reflecting box
box
{
	0, 1
	texture
	{
		pigment { color rgb 1 }
		finish { reflection 0.5 }
	}
	rotate y*45
	
	photons
	{
		target
		reflection on
		refraction off
		collect off
	}
}

// plain box
box
{
	0, 1.5
	texture
	{
		pigment { color rgb 1 }
	}
	rotate y*225

	photons
	{
		reflection off
		refraction off
		collect on
	}
}

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

light_source
{
	<-3,4,-5> color rgb 1
	photons { reflection off refraction off }
}

plane { y,0 texture { pigment { checker rgb 0, rgb 1 } } }

// end scene code

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Attachments:
Download 'photontest_spotlight.jpg' (9 KB) Download 'photontest_cylinder.jpg' (8 KB)

Preview of image 'photontest_spotlight.jpg'

Preview of image 'photontest_cylinder.jpg'

Hi Bruce, yes, something weird has happened I think. I wasn't getting too
involved at all with the beta testing during the last stages but I do see
that now Scenes\Advanced\optics.pov has changed. I had used the cylinder
spotlight in that scene file to keep a check on photons in media and now it
only renders half the beams it used to do. Try it and you'll see what I
mean. Sorry, but I haven't a clue what is going on.

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Thanks for the response, I have notice other odd things when using
cylinder lights with photons. Mainly incomplete 'beams' like in my
first example, or no photons being deposited at all.

But I must say, for me, photons is my favorite new feature in the
official pov. Until I try one of the others I suppose :) 



On Sun, 14 Jul 2002 06:23:27 -0500, "hughes b" <omn### [at] charternet>
wrote:

>Hi Bruce, yes, something weird has happened I think. I wasn't getting too
>involved at all with the beta testing during the last stages but I do see
>that now Scenes\Advanced\optics.pov has changed. I had used the cylinder
>spotlight in that scene file to keep a check on photons in media and now it
>only renders half the beams it used to do. Try it and you'll see what I
>mean. Sorry, but I haven't a clue what is going on.
>
>

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Hey, um, well heck... I rechecked using scenes\advanced\optics.pov again but
this time I realized I made an incorrect presumption. The cylinder light
radius was insufficient to stretch across both openings in the wall it beams
through (it's a bit offset in the +z, camera at +y?). That's why it appeared
as if half the light beam was showing. So that wasn't a problem after all.
In order to see that indeed the cylinder spotlight can be reflected at
various angles and then shone upon a wall try this. Add:

plane {x,0 pigment {rgb 1} finish {diffuse 1} rotate -30*z translate 3*x}
 // or rotate -45*z

to the end of the optics.pov file. Maybe increase the spotlight color to 3
so that the beam appears bright and that way you don't miss the effect. The
media won't show unless you make the plane hollow or -x but it's much faster
to render that way anyhow.
Fact is, it can do what is expected. What happens in your scene file is a
mystery to me still. I put the same global photons in and tried a few other
things to see if I could get the correct result. Nothing. I'm baffled. Could
be something simple I'm overlooking but I spent longer than I expected just
to check on it again so I figured I had covered all the bases.

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I knew I'd forget to mention you should increase the cylinder spotlight
radius and falloff about 3 times over the regular spotlight's to see it even
better still.

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