Hi there, its just me again!

I am modelling a little metal figurine (much like the well-known
wood-type
artists use as a sketch model). I did remember some posts a while ago,
where some people discussed things like using high rgb values for the
lightsources, but also low fade_distances and exponent in reflection.

I wanted to ask if there are some general strategies on how to find the
right setting, e.g. for the exponent (which was used as a specular
highlighting
simulation or something alike), fade_power and fade_distance etc.

So?

Tim

--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html

Post a reply to this message

If I remember my physics correctly, fade_power should be 2 in order to
reassemble reality.

/Anders

"Tim Nikias" <tim### [at] gmxde> wrote in message
news:3C4C53F4.FD2F2246@gmx.de...
> Hi there, its just me again!
>
> I am modelling a little metal figurine (much like the well-known
> wood-type
> artists use as a sketch model). I did remember some posts a while ago,
> where some people discussed things like using high rgb values for the
> lightsources, but also low fade_distances and exponent in reflection.
>
> I wanted to ask if there are some general strategies on how to find the
> right setting, e.g. for the exponent (which was used as a specular
> highlighting
> simulation or something alike), fade_power and fade_distance etc.
>
> So?
>
> Tim
>
> --
> Tim Nikias
> Homepage: http://www.digitaltwilight.de/no_lights/index.html
>
>

Post a reply to this message

> If I remember my physics correctly, fade_power should be 2 in order to
> reassemble reality.

But doesn't that depend on ones measuring of distance?  I personally use 1
unit = 1 centimeter but others do something else.

Hugo

Post a reply to this message

> > If I remember my physics correctly, fade_power should be 2 in order to
> > reassemble reality.
>
> But doesn't that depend on ones measuring of distance?  I personally use 1
> unit = 1 centimeter but others do something else.

No. The fade_power doesn't depend on the measuring of distance.
fade_distance takes care of that, I believe.

- Slime
[ http://www.slimeland.com/ ]
[ http://www.slimeland.com/images/ ]

Post a reply to this message

For ideal diffuse source (POV 3.5):

  fade_power 2 fade_distance sqrt(area-of-emitting-surface)
  spotlight radius -90 falloff 90 tightness 1

Dividing the source to multiple smaller sources improves
the intensity simulation for objects close to to the source.
Same applies when the shape of the source differs much from
circle or square.

When the source is not diffuse but directs light like a spot light
fade_distance should be increased. The modifier depends on the
spotlight parameters. For spotlight radius 0 falloff FO tightness 0
my guess for the modifier would be 90^2/FO^2, until I find
out how lighting engineers calculate spotlights.


_____________
Kari Kivisalo

Post a reply to this message

>
>   fade_power 2 fade_distance sqrt(area-of-emitting-surface)
>   spotlight radius -90 falloff 90 tightness 1
>

radius -90 ?! shouldn't that normally be something like radius >0?

But good explanation nontheless...

--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html

Post a reply to this message

Tim Nikias wrote:
>
> radius -90 ?! shouldn't that normally be something like radius >0?

Yes, normally. This is advanced stuff :) It's in the manual
but -90 is needed to enable cosine distribution for the spot light.
It's needed to simulate how the brightness and projected area of
planar diffuse source change as a fuction of viewing angle.


_____________
Kari Kivisalo

Post a reply to this message

> > > If I remember my physics correctly, fade_power should be 2 in order to
> > > reassemble reality.
> >
> > But doesn't that depend on ones measuring of distance?  I personally use
1
> > unit = 1 centimeter but others do something else.
>
> No. The fade_power doesn't depend on the measuring of distance.
> fade_distance takes care of that, I believe.


I don't understand that. According to the manual and to my experiences,
"fade_distance" is the distance from the light source at which the light
keeps a constant intensity.. After this distance has been reached, intensity
decreases with the speed of "fade_power".. I can't see this doesn't relate
to ones measuring of distance..


Hugo

Post a reply to this message

Hugo wrote:
>
> > The fade_power doesn't depend on the measuring of distance.
> 
> I don't understand that.

intensity = 2/( 1 + (d/fade_distance)^fade_power )

At the surface the intensity is 2 and at fade_distance the intensity
is 1. It's a continous smooth function. Take a scene and scale it by
10 but don't modify fade_power. You will see that fade_power doesn't
depend on the measuring of distance. 1/d^2 for intensity holds true
for point sources in RL, why not in povray.

The more complicated equation in povray simulates how light sources
with non-zero dimensions behave at close range. It's the result of
integrating multiple point sources over an area, I believe. When d
is large enough the equation simplifies to 1/d^2 (in a broad sense).

I verified that this equation works for planar diffuse sources:
http://news.povray.org/povray.binaries.images/19212/
I assumed of course, that povray radiosity works :)


_____________
Kari Kivisalo

Post a reply to this message

On Tue, 22 Jan 2002 14:14:26 +0100, "Hugo" <hua### [at] post3teledk> wrote:

>I don't understand that. According to the manual and to my experiences,
>"fade_distance" is the distance from the light source at which the light
>keeps a constant intensity.. 

It is IIRC the distance at which the light is at half its nominal
intensity.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

Post a reply to this message