I'm working on an experimental test image, involving a differenced sphere with a
chrome texture on the inner surface, and a hole cut in one side.

The sphere is surrounded by atmospheric media, and there is a light source
inside the cavity.

logic suggests that the only light effecting the media should be coming from the
hole, but the scene is a complete white-out.  It's as if the sphere is not
containing the light source at all, but allowing the rays to pass through it.

Even when the hole is removed from the sphere, and the light is completely
contained within, the scene whites out.

Is this a bug, or am I missing something?

A.D.B.

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Sorry to ask naive, simpleton questions from the get-go, but I'm just trying to
get a handle on the problem.

Which version of POV-Ray are you using?

Are you using scattering media? Not emission media, hopefully. ;-)

Are you sure the light is inside the sphere? (Believe me, I've had *that*
problem before, thinking the light is at one place when it's at another; I have
to resort to a looks_like sphere to locate it!)

If you remove any/all CSG *and* give the sphere just a simple pigment, does the
problem still occur?

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"Kenneth" <kdw### [at] earthlinknet> wrote:
> Sorry to ask naive, simpleton questions from the get-go, but I'm just trying to
> get a handle on the problem.
>
> Which version of POV-Ray are you using?
>
> Are you using scattering media? Not emission media, hopefully. ;-)
>
> Are you sure the light is inside the sphere? (Believe me, I've had *that*
> problem before, thinking the light is at one place when it's at another; I have
> to resort to a looks_like sphere to locate it!)
>
> If you remove any/all CSG *and* give the sphere just a simple pigment, does the
> problem still occur?

I'm currently running beta 39 in Ubuntu.  I am using a simple scattering media,
40 intervals, scattering { 3, White*10^-obsceneNumber } samples 30, 50

I did notice that pov crashes with an out of memory error if I use 400 intervals

I am certain the light source is inside the sphere, though I have not tried
removing the csg.

This is not a new problem.  I've experienced similar difficulties in the past
with light sources inside csg objects.

A.D.B.

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"Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> schreef in bericht 
news:web.4ce2500a9d76459e507e8a090@news.povray.org...
> I'm working on an experimental test image, involving a differenced sphere 
> with a
> chrome texture on the inner surface, and a hole cut in one side.
>
> The sphere is surrounded by atmospheric media, and there is a light source
> inside the cavity.
>
> logic suggests that the only light effecting the media should be coming 
> from the
> hole, but the scene is a complete white-out.  It's as if the sphere is not
> containing the light source at all, but allowing the rays to pass through 
> it.
>
> Even when the hole is removed from the sphere, and the light is completely
> contained within, the scene whites out.
>
> Is this a bug, or am I missing something?
>

Try this:
- contain the media only within the sphere
- if tthe sphere and media container are scaled up, devided the scattering 
color by the same amount. ex: media container scaled 100, then do scattering 
{scattering type, scattering color/100 gamma Gamma etc....}
- always use intervals 1 (default !!)
- start with samples 10 and increase if needed

Thomas

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"Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> schreef in bericht 
news:web.4ce267d76e7a50e8507e8a090@news.povray.org...
> I'm currently running beta 39 in Ubuntu.  I am using a simple scattering 
> media,
> 40 intervals, scattering { 3, White*10^-obsceneNumber } samples 30, 50
>
Be aware that intervals should always(!) be 1 and samples restricted to only 
one(!) value. Your code should thus be: scattering {3, 
White/MediaContainerScale} samples 50
Instead of white, try darker colors (<1.0) as that also influences the 
transparency of the media.

Thomas

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> "Kenneth"<kdw### [at] earthlinknet>  wrote:
>> Sorry to ask naive, simpleton questions from the get-go, but I'm just trying to
>> get a handle on the problem.
>>
>> Which version of POV-Ray are you using?
>>
>> Are you using scattering media? Not emission media, hopefully. ;-)
>>
>> Are you sure the light is inside the sphere? (Believe me, I've had *that*
>> problem before, thinking the light is at one place when it's at another; I have
>> to resort to a looks_like sphere to locate it!)
>>
>> If you remove any/all CSG *and* give the sphere just a simple pigment, does the
>> problem still occur?
>
> I'm currently running beta 39 in Ubuntu.  I am using a simple scattering media,
> 40 intervals, scattering { 3, White*10^-obsceneNumber } samples 30, 50
>
> I did notice that pov crashes with an out of memory error if I use 400 intervals
>
> I am certain the light source is inside the sphere, though I have not tried
> removing the csg.
>
> This is not a new problem.  I've experienced similar difficulties in the past
> with light sources inside csg objects.
>
> A.D.B.
>
>
Only use a single interval: don't change intervals from it's default 
value of 1.
Change the samples value, and only that value.
That way, it's MUCH faster!

Is your sphere set as no_shadow?
Do you use a looks_like for your sphere? In that case, the sphere is 
automaticaly no_shadow.

Be sure that you use an union of your light and the containing object.



Alain

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Anthony D. Baye wrote:

> Is this a bug, or am I missing something?

It would be helpful if you could post a small sample scene.

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Christian Froeschlin <chr### [at] chrfrde> wrote:
> Anthony D. Baye wrote:
>
> > Is this a bug, or am I missing something?
>
> It would be helpful if you could post a small sample scene.

basically:

#include "metals.inc"

light_source { 0.0 rgb 1 }

media {
    intervals 40
    scattering { 3, White*0.00001 }
    samples 30, 50
    }

difference {
    sphere { 0.0, 12.0 }
    sphere { 0.0, 11.625 texture { T_Chrome_5E } }
        texture { T_Chrome_3B }
    }

that's the gist of it.  The universal media whites out, even though the light is
inside the sphere.

A.D.B.

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"Anthony D. Baye" <Sha### [at] spamnomorehotmailcom> wrote:
> Christian Froeschlin <chr### [at] chrfrde> wrote:
> > Anthony D. Baye wrote:
> >
> > > Is this a bug, or am I missing something?
> >
> > It would be helpful if you could post a small sample scene.
>
> basically:
> [......]
> that's the gist of it.  The universal media whites out, even though the light is
> inside the sphere.

Running your code example in v3.6.1c, I wasn't able to reproduce the
problem--the scene is dark (as would be expected with the light being inside the
closed sphere.)

However, I constructed a somewhat similar CSG test scene of my own--and I'm
running into some decidedly odd behavior (different from your problem, though
they might be related.) Will post more about it ASAP, as soon as I can make
sense of it...

BTW, as has been noted, it's *much* faster to run the media with intervals 1,
samples 50 (for example)--actually 27-times faster than your intervals 40
samples 30,50! Another note: It seems that atmospheric media needs a rather high
samples count to look decent (plus, perhaps, some small amount of jitter as
well, to break up the visual banding.)

Also: Part of the documentation in section 3.3.2.1 "Atmospheric Media" seems to
be out of date (the part that says, "Pov-Ray cannot sample media along an
infinitely-long ray"); such media *does* show up even when there's no background
object whatsoever.

Ken

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> Christian Froeschlin<chr### [at] chrfrde>  wrote:
>> Anthony D. Baye wrote:
>>
>>> Is this a bug, or am I missing something?
>>
>> It would be helpful if you could post a small sample scene.
>
> basically:
>
> #include "metals.inc"
>
> light_source { 0.0 rgb 1 }
>
> media {
>      intervals 40
>      scattering { 3, White*0.00001 }
>      samples 30, 50
>      }
>
> difference {
>      sphere { 0.0, 12.0 }
>      sphere { 0.0, 11.625 texture { T_Chrome_5E } }
>          texture { T_Chrome_3B }
>      }
>
> that's the gist of it.  The universal media whites out, even though the light is
> inside the sphere.
>
> A.D.B.
>
>

You need to change your media as follow:
media {
     intervals 1 // Default value, this line can be removed.
     scattering { 3, White*0.00001 }
     samples 120 // Only the first value is ever used.
// any second samples value is always ignored.
     }

This gives you the same number of samples but renders MUCH faster.



Alain

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