That is a learned and intelligible piece of information, Kenneth. Thank you 
indeed.

I have been experimenting with atmosphere and media clouds, but not to the 
extend of you or Abe, Roman or Kirk, and mostly following the directives of 
others, so my understanding is limited. Could you tell me if all this is 
also related to media boxes placed one behind the other (without surrounding 
atmosphere) which makes them visible (problem mentioned by Gilles Tran on 
his website)?

Thomas

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"Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> That is a learned and intelligible piece of information, Kenneth. Thank you
> indeed.
>
> I have been experimenting with atmosphere and media clouds, but not to the
> extend of you or Abe, Roman or Kirk, and mostly following the directives of
> others, so my understanding is limited. Could you tell me if all this is
> also related to media boxes placed one behind the other (without surrounding
> atmosphere) which makes them visible (problem mentioned by Gilles Tran on
> his website)?
>
> Thomas

I remembered that Bruno had done a lot of atmosphere experimentation some months
ago--did he ever post any code about his methods?  If not, would he be willing
to do so now and enlighten us all?  :)

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> 1) When there are two media objects, one inside the other (like your cloud oval
> inside your atmosphere), the larger enclosing sphere's media samples value
> completely overrides the smaller sphere's (and, I believe, its method and
> intervals as well.) You can test this by giving your cloud media samples 1000,
> and your atmosphere samples 1.  It will render lightning fast--and look
> terrible! Reverse the order, and BOTH spheres' media take on samples 1000. Or
> more generally, both spheres' medias seem to be treated as one, samples-wise.

What happens if two spheres intersect, but none is completely inside the 
other? Which sample count remains?

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"Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> That is a learned and intelligible piece of information, Kenneth. Thank you
> indeed.

Happy to help!
>
> Could you tell me if all this is
> also related to media boxes placed one behind the other (without surrounding
> atmosphere) which makes them visible (problem mentioned by Gilles Tran on
> his website)?
>

I don't think I've come across what you describe, in my own scenes.  Can you
post a link to the relevant page on Gilles's site? I'm curious to know what that
is.

I *did* set up a test scene, though, using spheres instead of boxes; one large
media sphere, plus a smaller one that I "orbited" around it
into different positions. (I made sure that the sphere surfaces didn't
intersect or even touch.)  I didn't see anything odd when the small sphere was
in front or in back of the large one, even when giving the spheres wildly
different samples values. Perhaps Gilles's boxes were actually intersecting?

Ken

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"Kenneth" <kdw### [at] earthlinknet> schreef in bericht 
news:web.47f1d20f91cbe45978dcad930@news.povray.org...
>> Could you tell me if all this is
>> also related to media boxes placed one behind the other (without 
>> surrounding
>> atmosphere) which makes them visible (problem mentioned by Gilles Tran on
>> his website)?
>>
>
> I don't think I've come across what you describe, in my own scenes.  Can 
> you
> post a link to the relevant page on Gilles's site? I'm curious to know 
> what that
> is.
>

It is the MakeCloud page:
http://www.oyonale.com/modeles.php?lang=en&page=36
You are right. Gilles mentions the problem with intersecting containers. 
However, I have met instances with Gilles' MakeCloud macro, where even with 
non-intersecting containers, those still became visible. Very frustrating.

Thomas

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Nicolas Alvarez <nic### [at] gmailisthebestcom> wrote:

> What happens if two spheres intersect, but none is completely inside the
> other? Which sample count remains?

This is where things get tricky (and is a notorious example of one's sphere's
outline showing up in the other.) The "overlapping" parts of
the two spheres' medias is determined by the samples count of the "larger" of
the two...and/or by which sphere the camera ray hits first, I believe. Visible
sphere outlines arise when samples in the two spheres are unequal (and just too
low); making the samples equal--though not necessarily high--usually eliminates
that. ("Equal" depends on the relative sizes of the spheres, though.) The parts
of the spheres that are NOT intersecting take on their own individual samples
count...though the camera position may have something to do with that
as well.

The worst-case scenario seems to be when the two spheres intersect and the
intersection surfaces are seen "edge on" so to speak--what looks like a convex
lens shape. I've had to really pump up (equal) samples counts in the two to fix
that; just increasing one or the other won't do it.

Ken W.

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"Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> "Kenneth" <kdw### [at] earthlinknet> schreef in bericht
>
> > Can you post a link to the relevant page on Gilles's site? I'm curious to know
> > what that is.
> >
>
> It is the MakeCloud page:
> http://www.oyonale.com/modeles.php?lang=en&page=36
> You are right. Gilles mentions the problem with intersecting containers.
> However, I have met instances with Gilles' MakeCloud macro, where even with
> non-intersecting containers, those still became visible. Very frustrating.
>
> Thomas

Thanks for that--my first introduction to df3 files.  Fascinating! I downloaded
the stuff and ran his makecloud1_demo file as-is, using his media parameters
(intervals 3, with method and samples left out.) But I didn't see anything odd
in that particular scene. I then changed his media to intervals 1 method 3
samples 1, and upped the cloud count--LOTS of overlapping boxes--just to really
wring it out!  Still no problems--which I found quite amazing,
actually. I *did* notice that he had max_trace_level set at 256. (Wow!)

Is there a particular demo that's causing problems for you?

Ken W.

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"Kenneth" <kdw### [at] earthlinknet> wrote:
> "Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> >
> > Gilles mentions the problem with intersecting containers.
> > However, I have met instances with Gilles' MakeCloud macro, where even with
> > non-intersecting containers, those still became visible. Very frustrating.
> >
> > Thomas
>
> ...I then changed his media to intervals 1 method 3
> samples 1, and upped the cloud count--LOTS of overlapping boxes--just to really
> wring it out!  Still no problems--which I found quite amazing,
> actually...
>

Oh, I finally did see *one* little flaw, but I had to look hard to find it!
Slightly upping the samples count got rid of it.

It occured to me that, the way his code is set up in the makecloud1_demo, there
is only one real media cloud definition, duplicated a bunch of times in his
#while loop.  Thus all the clouds automatically have the same # of samples.
I'm willing to bet that if each cloud had a random #, there would be visible
box intersection lines all over the place!

Ken W.

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"Kenneth" <kdw### [at] earthlinknet> schreef in bericht 
news:web.47f212a691cbe45978dcad930@news.povray.org...
>
> Is there a particular demo that's causing problems for you?
>
I met the problem with a couple of scenes of my own, years ago. I took the 
trouble to render the container boxes, just to check if they overlapped or 
not, but the problem remained. However now, your mention of max_trace_level 
and upping the samples might probably the solution. When I have time, I 
shall go back to those scenes and see what happens.

Thanks for mentioning this.

Thomas

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"Kirk Andrews" <kir### [at] tektonartcom> wrote:
> "Thomas de Groot" <t.d### [at] internlDOTnet> wrote:
> > That is a learned and intelligible piece of information, Kenneth. Thank you
> > indeed.
> >
> > I have been experimenting with atmosphere and media clouds, but not to the
> > extend of you or Abe, Roman or Kirk, and mostly following the directives of
> > others, so my understanding is limited. Could you tell me if all this is
> > also related to media boxes placed one behind the other (without surrounding
> > atmosphere) which makes them visible (problem mentioned by Gilles Tran on
> > his website)?
> >
> > Thomas
>
> I remembered that Bruno had done a lot of atmosphere experimentation some months
> ago--did he ever post any code about his methods?  If not, would he be willing
> to do so now and enlighten us all?  :)

Hi there!

Thanks Kirk for remembering me though I was away from you for a while!

As you said, I was studying atmosphere and clouds for the project I have in
mind: TerraPOV. I was honored to be encouraged by Jaime himself! The reason why
of this absence is that I was (pre)occupied about personal concerns (among
others: procedural, long and difficult divorce, hasta la vista ...), but still
on the subject.

I also assembled a config based on Q6600 Quad and installed Water Cooling last
week. I got 3.6 GHz overclock stable for POV (not 100% stable with CPUStress,
but it is very violent). Media takes ages to render if you want accurate
results.

I recently came back here to see what's going on, because I am about to write a
series of posts about the results of my study and the techniques for atmosphere
and clouds I intend to use in TerraPOV.

I will soon start with Chapter 1: Atmosphere (following physical reality as much
it is possible and reasonably feasible with POV).

Here is a recent result without radiosity but not one of the last (I am at work
while writing these lines and the last renders are at home)

See you very soon!

    Regards

        Bruno

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