"Tom York" <alp### [at] zubenelgenubi34spcom> wrote:
> "Dennis Clarke" <dcl### [at] blastwaveorg> wrote:
> > I see the all of that spec and wonder how much of it is optional parameters
> > or are they all needed ?  The vertical bar between parameters seems to
> > indicate "OR" but I am not sure.  It seems as if _everything_ is optional.
>
> Back in "the good old days" when media's predecessor system (known as halo)
> was around,

  That seems to ring a bell somewhere ... way back in the dusty corners
 of my head :-)

> there was an excellent tutorial/walkthrough that used an
> explosion as an example with which to demonstrate the basic syntax and use
> of this sort of effect. It was probably replaced by documentation section
> 2.3.6 (in povray 3.6.1, at any rate), which you may want to check out, it
> has many useful examples.

Ah ha !

http://www.blastware.org/docs/html/s_71.html#s02_03_06
2.3.6 Simple Media Tutorial

How could I have missed that .. geez ...

> An absolutely minimal media (medium?) would look something like the
> following. You have a container object that must be declared to be hollow,

  Oh?  I guess in my mind I think of a fog bank as being "everywhere" and
smoke would be the same.  I guess in any computer based representation I
would need to contain the mathematical model of smoke in some bounded
manifold.  Makes perfect sense although not intuitive.

> (usually) with a completely transparent surface. The absolute minimum
> required for the media definition is a declaration of the type of media
> you're using, with any requirements that statement involves.
>
> sphere {
>   <0,0,0>, 1
>
>   hollow on
>
>   texture { pigment { colour rgbt 1 } }
>
>   interior {
>     media {
>       emission <1,1,1>
>       // OR:  absorption <1,1,1>
>       // OR:  scattering { 1, <1,1,1> }
>     }
>   }
> }
>
> Everything else is optional, but not necessarily ignorable.

 I see that now.  :-)

> > I am trying to put together a trivial example of media in which a beam of
> > light would be scattered in much the same way that a flashlight beam would
> > be in a dark night with heavy fog or smoke.
>
> In my experience, emission media is almost always trivial, absorption media
> is less so, and scattering media is highly non-trivial.

Oh dear.  Well, I know that I am thinking of a combination of absorption and
scattering at the same time.  That should keep my CPU busy.

> Check out those
> examples in the documentation and see if any of them serve your needs.

I will definately climb on top of that.

> Things I remember that may not be obvious: scattering media, far more than
> the other two types, can be extremely time-consuming to render and hence
> difficult to adjust.

I have been placing objects in the scene files and then doing renders with
the +Q5 option for quality.  That gives me object placement and not too
much else.

Then I have been doing "quick" renders at full +Q9 with 800x600 images and
then my test images are at 4096x3072.  Needless to say the final images are
taking an hour or so with a lot of reflection and refraction on some glass
objects.  I am happy with the result thus far and want to now add in the
smoke effect with search beams.

> It may require extremely high sampling parameters to
> capture shadows cast by light sources. Scattering media is *not*
> illuminated by shadowless lights (which is another thing they oddly fail to
> do).

OKay .. that is odd.  I keep thinking of smoke as particles but in reality
its not the case.  I think to actually model smoke one would need several
trillion tiny spheroids with a supercomputer ( BlueGene ) to perform the
render.

Thanks for the input and I hope to follow up this thread with some results.

Dennis

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