Hi.
I'm trying to make cigarette smoke.

The yellow object in http://thyme.homelinux.net/still-life-nm.jpg
is just to show the shape I'm using for the smoke.
It's a csg merge of lots of sphere sweeps. It does have a fairly
irregular surface which I think may be the problem.

The second image  http://thyme.homelinux.net/still-life-bm.jpg
shows lots of what look like artefacts when I turn on media.

the relevant code for both is:

    #if (Quick)
        pigment { rgb<1,1,0> }
    #else
        hollow
        texture { pigment { rgbt<1.0, 1.0, 1.0, 1> } }
        interior {
            media {
                // samples 4, 4
                // method 3
                // intervals 1
                // scattering { 2 0.5 }
                absorption 0.7
                emission 0.7
            }
        }
    #end

I have max_trace_level 50 in my global_settings, so I guess I
have to play around with media options. I've been testing various
settings for samples, method and interval for the last day or so,
they seem to change the effect but nothing I've tried so far
fixes it.

Has anyone seen this before?

-- 
Bill Hails

Post a reply to this message

Bill Hails wrote:
> 
> Hi.
> I'm trying to make cigarette smoke.

http://www.studenter.hb.se/~arch/smokegen/index.htm

-- 
Ken Tyler

Post a reply to this message

Ken wrote:

> 
> http://www.studenter.hb.se/~arch/smokegen/index.htm
> 

Hi, thanks, I didn't know about that one. I'll try it out.
It's not so much fun when you aren't doing it yourself though :-)

-- 
Bill Hails

Post a reply to this message

Bill Hails wrote:
> 
> Ken wrote:
> 
> >
> > http://www.studenter.hb.se/~arch/smokegen/index.htm
> >
> 
> Hi, thanks, I didn't know about that one. I'll try it out.
> It's not so much fun when you aren't doing it yourself though :-)

I was hoping that you could learn by example. You don't have to use
it, just learn from it :)

-- 
Ken Tyler

Post a reply to this message

"Bill Hails" <bil### [at] europeyahoo-inccom> wrote in message
news:3ebe7e73@news.povray.org...
> Hi.
> I'm trying to make cigarette smoke.
>

It almost looks as though the surface of the container is reflecting something
(a checkered floor no less - how traditional ;).

Any stray settings floating around?

Post a reply to this message

Tom Melly wrote:

> It almost looks as though the surface of the container is reflecting
> something (a checkered floor no less - how traditional ;).
> 
> Any stray settings floating around?

nope, very standard, except for the big max_trace_level = 50.
I'm trying a different tack atm, but I think it may be a bijoux bugette in 
Pov. I had

#declare Cigarette = union {
        // parts of the cigarette
        ...
        SmokeShape
}

where SmokeShape is a merge of some sphere sweeps with media turned on.

when I changed to:

#declare Cigarette = merge {
        // parts of the cigarette
        ...
        SmokeShape
}

the artefacts disappeared (but other problems occurred).

I can't swear to this, it was late at night :-) but the
SmokeShape certainly rendered perfectly well by itself
with media turned on.

The artefacts do look like a chequered floor, I think that's
indicative, like they appear when the ray passes an even (odd?) number
of times through the object?

I guess I'd be doing everyone a favour if I could produce
a sample piece of code exhibiting the problem - I'm feeling
a little guilty now, I'll see what I can do.

-- 
Bill Hails

Post a reply to this message

On Tue, 13 May 2003 15:04:56 -0500, Bill Hails wrote:
> 
> The artefacts do look like a chequered floor, I think that's indicative,
> like they appear when the ray passes an even (odd?) number of times
> through the object?
> 
> 
> 

I think you're probably on the right track... If you look at section
6.5.6.5 of the povray manual (about the CSG merge operation), you'll see
the following:

"The union operation just glues objects together, it does not remove the
 objects' surfaces inside the union. Under most circumstances this doesn't
 matter. However if a transparent  union is used, those interior surfaces
 will be visible. The  merge operations can be used to avoid this problem.
 It works just like union but it eliminates the inner surfaces..."

I'm not really familiar with how media functions with container objects,
but I wouldn't be at all surprised to find that your problem was related
to the surfaces that weren't removed by the union, AND that it's not
really a bug.  ;)

Good luck with it!

	-Ed

Post a reply to this message

Ed Jackson wrote:

> On Tue, 13 May 2003 15:04:56 -0500, Bill Hails wrote:
>> 
>> The artefacts do look like a chequered floor, I think that's indicative,
>> like they appear when the ray passes an even (odd?) number of times
>> through the object?
>> 
>> 
>> 
> 
> I think you're probably on the right track... If you look at section
> 6.5.6.5 of the povray manual (about the CSG merge operation), you'll see
> the following:
> 
> "The union operation just glues objects together, it does not remove the
>  objects' surfaces inside the union. Under most circumstances this doesn't
>  matter. However if a transparent  union is used, those interior surfaces
>  will be visible. The  merge operations can be used to avoid this problem.
>  It works just like union but it eliminates the inner surfaces..."
> 
> I'm not really familiar with how media functions with container objects,
> but I wouldn't be at all surprised to find that your problem was related
> to the surfaces that weren't removed by the union, AND that it's not
> really a bug.  ;)
> 
> Good luck with it!

Thanks.

The smoke is already a merge however, not a union. The artefacts appear when
I use the smoke object within a bigger union (cigarette + smoke).

I'll try and get a test example out tonight/this weekend

> -Ed

-- 
Gee Batman, is there *anything* you don't understand?
Yes Robin, several things.

Post a reply to this message