Hi

Does anyone know of any decent tutorials into the use of media (unless I've
missed something the tutorials in the docs doesn't cover this)? I've used
emitting media in the past for a candle and it seemed quite effective but
I'm now interested in the use of scattering media. I tried making a sphere
containing media around a light source (which appears to be a fairly
standard technique) but I ended up (6 hours 2 minutes and 34 seconds later)
with a scene that looked worse than it did before I decided to experiment! I
thought that a tutorial might help teach me what media can acheive and how
to use it but I've found links to 2 (and possibly a third) tutorials from
multiple locations all of which appear to be dead links :( Are there any
tutorials out there which could help me?

Thanks in advance for any help you are able to give me.

Post a reply to this message

"John Vodden" <jav### [at] gmxcouk> wrote in message
news:3d4c5479$1@news.povray.org...
>
> Does anyone know of any decent tutorials into the use of media (unless
I've
> missed something the tutorials in the docs doesn't cover this)? I've used
> emitting media in the past for a candle and it seemed quite effective but
> I'm now interested in the use of scattering media. I tried making a sphere
> containing media around a light source (which appears to be a fairly
> standard technique) but I ended up (6 hours 2 minutes and 34 seconds
later)

I'm without the IE Favorites I had amassed over time but you might get some
insight by looking over a page about "realistic water" at
http://www-public.tu-bs.de:8080/~y0013390/raytracing.html

Thing about media is that it varies so much when used in different ways, not
easy to apply it in one way for all uses. Object media is one way,
atmosphere is another. I'd say you went with the latter and filled a room
with it or at least a larger area around a light_source. Either that or you
have a PC like I had so many years ago and everything is slow. Just kidding.

In version 3.5, if you are now using that, you should be letting intervals
alone usually. Media doesn't require intervals 10 like it did in v3.1. In
fact I get fairly good results by leaving out all the sampling parameters so
everything is default, unless the media has artifacts. You could also use
either of the three methods, 'method 2' being faster usually.

Remember that you can always try one of the demo scene files
(scenes\advanced\interior\) to see how the media is applied and how it
looks, tweaking on stuff as you go along. If I recall correctly, the files
named hollow will show object examples and the ones named media show
atmospheric.

Post a reply to this message

"hughes b" <omn### [at] charternet> wrote in message
news:3d4c982d@news.povray.org...
> "John Vodden" <jav### [at] gmxcouk> wrote in message
> news:3d4c5479$1@news.povray.org...

> In version 3.5, if you are now using that, you should be letting intervals
> alone usually. Media doesn't require intervals 10 like it did in v3.1. In
> fact I get fairly good results by leaving out all the sampling parameters
so
> everything is default, unless the media has artifacts. You could also use
> either of the three methods, 'method 2' being faster usually.

The docs suggest that "intervals 10" is the default value anyway but I shall
play around with the different methods and see what things look like.

> Remember that you can always try one of the demo scene files
> (scenes\advanced\interior\) to see how the media is applied and how it
> looks, tweaking on stuff as you go along. If I recall correctly, the files
> named hollow will show object examples and the ones named media show
> atmospheric.

Ah, thank you for that, I didn't realise quite how many demo scene files
came with povray! Looking at those has proved very useful, I had the
scattering at rgb <1,1,1> so it was extremely intense. It hadn't occured to
me to reduce this (in the same way as you do with lights) to make it less
intense, I thought that would be a density issue.

Post a reply to this message

"John Vodden" <jav### [at] gmxcouk> wrote in message
news:3d4d1293$1@news.povray.org...
>
> The docs suggest that "intervals 10" is the default value anyway but I
shall
> play around with the different methods and see what things look like.

For method 3, the default method, it starts at 1 and increases if needed. So
that one is kind of automatic.

> scattering at rgb <1,1,1> so it was extremely intense. It hadn't occured
to
> me to reduce this (in the same way as you do with lights) to make it less
> intense, I thought that would be a density issue.

Simply put, density can be used alone to control any emission and/or
absorption being used to act as a kind of fog. Scattering can be used alone
or with those things for interacting with the light sources in various ways.
And that's about as simplistic as it gets until you try going about doing
something with it.
That was kind of a joke, BTW. I think most the difficulty is not knowing
when to settle for a certain appearance. Seriously though, I still struggle
along when I think I'm going to brighten up the air with media and
everything goes dark instead.

Post a reply to this message

In article <3d4d1293$1@news.povray.org>, "John Vodden" <jav### [at] gmxcouk> 
wrote:

> Ah, thank you for that, I didn't realise quite how many demo scene files
> came with povray! Looking at those has proved very useful, I had the
> scattering at rgb <1,1,1> so it was extremely intense. It hadn't occured to
> me to reduce this (in the same way as you do with lights) to make it less
> intense, I thought that would be a density issue.

This is the one thing that caused me the most trouble when I was first 
trying to figure out media. It took me a while to realize that the same 
value controlled both color and density, and that the "density" stuff 
was just to pattern the density.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

Post a reply to this message

"Christopher James Huff" <chr### [at] maccom> wrote in message
news:chr### [at] netplexaussieorg...
> In article <3d4d1293$1@news.povray.org>, "John Vodden" <jav### [at] gmxcouk>
> wrote:
>
> This is the one thing that caused me the most trouble when I was first
> trying to figure out media. It took me a while to realize that the same
> value controlled both color and density, and that the "density" stuff
> was just to pattern the density.
>
So would I be right in thinking that the colour will set the max density and
the "density" will make a pattern with densities less than and up to that?
(not the nicest way of phrasing it I'm sure!)

I don't know what I did to make it take 6 hours... I've had a play with it
(both in the original scene and with a few "spheres above planes") and it
doesn't take anything like that long. WIERD :)

Post a reply to this message

In article <3d4d94b1@news.povray.org>, "John Vodden" <jav### [at] gmxcouk> 
wrote:

> So would I be right in thinking that the colour will set the max density and
> the "density" will make a pattern with densities less than and up to that?
> (not the nicest way of phrasing it I'm sure!)

Not quite...the densities are multiplied together. If you use values 
between 0 and 1 in the density portion (in the color_map, for example), 
the actual density will range between 0 and the constant color you gave 
with the scattering, emission, and/or absorption keywords. With solid 
media (with no density pattern) I usually use COLOR*DENSITY for the 
constant value, which makes it easy to separately adjust the color and 
density of the media. With patterned densities, I use the density 
statement to provide the color, and the constant value for the density.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

Post a reply to this message