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  A halo in a lightbeam in a room with atmosphere (Message 1 to 5 of 5)  
From: Harmen Mesker
Subject: A halo in a lightbeam in a room with atmosphere
Date: 17 May 1998 02:43:45
Message: <6jm0ur$347$1@oz.aussie.org>
Does anybody know if it's possible to
1. have a scene with the atmosphere option on
2. place a spotlight (making the atmosphere visible in the shape of a
cone)
3. place a (hollow) sphere with a halo in it in that lightbeam?

When I do this, the sphere itself, instead of the halo, becomes
visible as a bright white circle. When I place the sphere outside the
lightbeam the halo becomes visible; when I place the sphere only for a
part in the lightbeam, only the part in the lightbeam lights up, the
part outside the lightbeam shows the halo I want.

In other words: is it possible to show a halo in a lightbeam, with
atmosphere turned on?

Greetings,

Harmen Mesker.
------------------------------------------
You are welcome at my new Yi Jing Page:
http://www.cybercomm.nl/~hmesker
------------------------------------------


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From: Johannes Hubert
Subject: Re: A halo in a lightbeam in a room with atmosphere
Date: 17 May 1998 07:59:31
Message: <6jmjft$41e$1@oz.aussie.org>
Is it possible, but give the sphere a totally invisible texture in addition
to the halo, like:

texture  // invisible

      pigment
      {
         color rgbft <1.0, 1.0, 1.0, 1.0, 1.0>
      }
      finish
      {
         ambient 0.0
         diffuse 0.0
      }
}

The effect you describe is the hollow sphere itself showing in the
lightbeam.

Hope it helps,
Johannes.


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From: Harmen Mesker
Subject: Re: A halo in a lightbeam in a room with atmosphere
Date: 17 May 1998 10:16:30
Message: <6jmrgq$4ad$1@oz.aussie.org>
Dear Johannes,

If tried this, but unfortunately this didn't help. This is an example
of source code which produces the wrong result:

/* Here it starts

global_settings {
  adc_bailout 0.003922
  ambient_light <1.0,1.0,1.0>
  assumed_gamma 1.9
  hf_gray_16 off
  irid_wavelength <0.247059,0.176471,0.137255>
  max_intersections 64
  max_trace_level 10
  number_of_waves 10
}

background { color <0.000,0.000,0.000> }

atmosphere {
  type 1
  distance     40.0
  color <0.8,0.8,1.0,0.0,1.0>
  scattering   0.3
  samples      5
  jitter       0.0
  aa_threshold 1.0
  aa_level     3
}

camera {
  location  <-12.000, -20.000, 15.000>
  direction <0.0,     0.0,  1.8317>
  sky       <0.0,     0.0,  1.0>
  up        <0.0,     0.0,  1.0>
  right     <1.33333,  0.0,  0.0>
  look_at   <0.000, 0.000, 0.000>
}

light_source {
  <0.000, 0.000, 18.812>
  color  rgb <1.000, 1.000, 1.000>
  spotlight
    point_at  <0.000, 0.000, 17.812>
    falloff   9.22
      radius    4.66
}

#declare Texture =
   texture
   {
      pigment
      {
         color rgbft <1.0, 1.0, 1.0, 1.0, 1.0>
      }
      finish
      {
         ambient 0.0
         diffuse 0.0
         brilliance 0.0
         phong_size 0.0
         roughness 0.0
      }
      halo
      {
         emitting
         linear
         spherical_mapping
         color_map
         {
            [ 0.0     rgbft <1.0, 1.0, 0.0, 0.0, 1.0> ]
            [ 0.088968  rgbft <1.0, 1.0, 0.0, 0.0, 0.0> ]
            [ 0.373665  rgbft <1.0, 0.0, 0.0, 0.0, 0.0> ]
            [ 1.0     rgbft <1.0, 0.0, 0.0, 0.0, 1.0> ]
         }
         turbulence 1.0
         scale  0.5
      }
   }

sphere

  <0,0,0>,1
  texture {
    Texture
  }
  hollow
  scale 2.297393
}

*/ here it ends

If I comment out the atmosphere section, the halo does show up. Maybe
you can find the error in the source code?

Thanks for your help,

Greetings,

Harmen.


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From: Mike Hough
Subject: Re: A halo in a lightbeam in a room with atmosphere
Date: 17 May 1998 11:45:17
Message: <355F060C.7F7B9D88@aol.com>
If you use a filter of 0 and transmit of 1 the halo starts to show up,
but the real problem is that the scattering is too high.  A lot of people
do this starting out.  Generally I start with a scattering or .05 and go
from there.  The only other problem is that the halo container is
slightly visible.  This is something hard to fix, but adjusting the
transmission of the pigment of the sphere can hide it somewhat.  Here's
your source code with a few modifications:

global_settings {
  adc_bailout 0.003922
  ambient_light <1.0,1.0,1.0>
  assumed_gamma 1.9
  hf_gray_16 off
  irid_wavelength <0.247059,0.176471,0.137255>
  max_intersections 64
  max_trace_level 10
  number_of_waves 10
}

background { color <0.000,0.000,0.000> }


atmosphere {
  type 1
  distance     40.0
  color <0.8,0.8,1.0,0.0,1.0>
  scattering   0.05
  samples      5
  jitter       0.0
  aa_threshold 1.0
  aa_level     3
}


camera {
  location  <-12.000, -20.000, 15.000>
  direction <0.0,     0.0,  1.8317>
  sky       <0.0,     0.0,  1.0>
  up        <0.0,     0.0,  1.0>
  right     <1.33333,  0.0,  0.0>
  look_at   <0.000, 0.000, 0.000>
}

light_source {
  <0.000, 0.000, 18.812>
  color  rgb <1.000, 1.000, 1.000>
  spotlight
    point_at  <0.000, 0.000, 17.812>
    falloff   9.22
      radius    4.66
}

#declare Texture =
   texture
   {
      pigment
      {
         color rgbft <1.0, 1.0, 1.0, 0, .8>
      }
      finish
      {
         ambient 0.0
         diffuse 0.0
         brilliance 0.0
         phong_size 0.0
         roughness 0.0
      }
      halo
      {
         emitting
         linear
         spherical_mapping
         color_map
         {
            [ 0.0     rgbft <1.0, 1.0, 0.0, 0.0, 1.0> ]
            [ 0.088968  rgbft <1.0, 1.0, 0.0, 0.0, 0.0> ]
            [ 0.373665  rgbft <1.0, 0.0, 0.0, 0.0, 0.0> ]
            [ 1.0     rgbft <1.0, 0.0, 0.0, 0.0, 1.0> ]
         }
         turbulence 1.0
         scale  0.5
      }
   }

sphere {

  <0,0,0>,1
  texture {
    Texture
  }
  hollow
  scale 2.297393
}

P.S I had a little fun with it and changed the halo to a dust halo.
Looks pretty neat

halo
      {
         dust
         linear
         spherical_mapping
         color_map
         {
            [ 0.0     rgbft <1.0, 1.0, 0.0, 0.0, 1.0> ]
            [ 0.088968  rgbft <1.0, 1.0, 0.0, 1.0, 0.0> ]
            [ 0.373665  rgbft <1.0, 0.0, 0.0, 1.0, 0.0> ]
            [ 1.0     rgbft <1.0, 0.0, 0.0, 0.0, 1.0> ]
         }
         turbulence 1.0
         scale  0.5
      }


Harmen Mesker wrote:

> Dear Johannes,
>
> If tried this, but unfortunately this didn't help. This is an example
> of source code which produces the wrong result:
>

<snip>

> If I comment out the atmosphere section, the halo does show up. Maybe
> you can find the error in the source code?
>
> Thanks for your help,
>
> Greetings,
>
> Harmen.


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From: Nathan Kopp
Subject: Re: A halo in a lightbeam in a room with atmosphere
Date: 18 May 1998 00:03:36
Message: <355FB318.9BAB2F98@ltu.edu>
POV's halos have many problems, IMHO.  I've experienced similar problems with
halo container objects showing up when atmosphere is used.  Fortunately, the
next version of POV (3.1) is trashing halos altogether and going with something
similar (but very much better) called "media".  I'm looking forward to the
change.  :)

-Nathan Kopp


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