POV-Ray : Newsgroups : povray.binaries.tutorials : Re: Where are my lights???? : Re: Where are my lights???? Server Time
30 May 2023 11:09:40 EDT (-0400)
  Re: Where are my lights????  
From: Dave Helfrich
Date: 9 Apr 1999 23:50:45
Message: <370ebc85.0@news.povray.org>
Thanks for the tips...
First of all though, the cylinders that the lights fall in are (supposedly)
clear.  I tried using the "no_shadow" option on them as well, to no avail.

The center is a series of concentric discs, immediately followed by a thin
ring (difference of 2 cylinders.)  The outer most ring is also a difference
of 2 cylinders.  The large ring between them is actually a cylinder, <0, -3,
0>, <0, 1, 0> that is differenced from a plane (y= -0.5).  The large ring
does have a texture because I didn't want the green of the plane to show
there.  But if it's got the "no_shadow" option on it, why wouldn't the
lights shine through?  I think I'm going to try to give that large inner
ring a clear texture and see if that helps.

Secondly, I also tried raising the light sources up along the y axis.. as
high as y=10, which should have taken them well above any of the rings.
Still didn't help.

Thirdly, the camera angle I used in this was so I could get a "bird's eye"
view of the scene.  I don't generally render scenes at that angle...  I do
it on occasion just to get a look at how things are placed when I'm having
difficulties (as I was with this one).  I haven't had any problems yet doing

There are actually more objects in this scene, but I commented them out
while in an attempt to isolate what was blocking the light sources.  When I
sent the sample code, I didn't include those objects.  (Otherwise there'd be
something like 500 or so lines of code commented out.)

Thanks for your tips...  I'll play with it some more and see what I can do.


Ken wrote in message <370D82E5.175D0F9A@pacbell.net>...
>  I took a look at your scene file and think I can explain your
>proceedural misunderstanding. I would have tried rendering it
>after making some changes but I am rendering a scene while on line
>and don't want to stop it right now.
>  You have each of your disks located at y = 0. You also have a
>couple of cylinders at y = 0 that are at least 1/2 a pov unit thick
>(I didn't memorize all of the paramaters of your scene so bear with
>me on my generalizations}. Now you have added several cylinder light
>sources ringing this construction all at a uniform distance of 80 units
>or so and each is lying on the y = 0 zero plane. All I can tell you is
>that in pov, as it is in real life, light cannot travel through solid
>objects and that is what you are expecting them to do with the current
>arrangement. Add a positive y value to your light statements and they
>should start to work. I am almost certain that is your problem.
>They are specified now as:
> light_source { <0, 0, 80 > stuff }
>Try changing them to:
> light_source { <0, 3, 80 > stuff }
>and see if that makes a difference in their perfomance.
>Also when I checked to see what camera position you are using
>I noticed that you have your camera at:
>camera { location < 0, 200, 0 > look_at <0,0,0>}
>You are very lucky that this alone is not crashing the program. In
>most cases it causes a divide by zero error and the program terminates
>with a program fualt. Even if you are getting away with it now it is not
>a good practice to continue. If you need a straight overhead position
>like this always add a very small amount of -z to the camera location.
>camera { location < 0, 200, -0.0001 > look_at <0,0,0>}
>That very tiny amount will keep the program from having the divide by
>zero problem and will in all but the most extreme cases be totaly
>undetectable in the way the scene looks when rendered.
>Ken Tyler

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