I'm not sure if this question would be considered for "advanced" users or not,
but: Is it possible to cast caustics from an object without seeing things
reflected in its surface?

I am modeling a planet, and I would like to see reflected light illuminating the
dark side of one of its moons. I briefly tried radiosity, but photon mapping
seemed more accurate.

My problem is that I don't want to see objects reflected in the surface of the
planet; I only want the caustics it casts. ...Is this outright impossible?

Below is a boiled-down version of my scene code.
Thanks, God bless!

------

#local sun_radius      =   40.00; // units in meters*10^6
#local plan_orbt_rdus  = 3000.00; // planet's orbit radius
#local aphelion_offset =   20.00; // distance of ephelion from otherwise
circular orbit
#local plan_radius     =    6.53;
#local plan_moon_dist  =    6.00; // dist @ closest point between moon's
surfaces
#local plan_moon_rdus  =    6.22; // moon radius
#local plan_rotn_prod  =    4.70; // rotation period in hours
#local camr_dist       =    3.00; // multiplier for camera dist
#local plan_poso = radians(073);  // planet's orbital position in radians
counterclockwise from positive x axis
#local plan_day  = 0;             // planet's rotational position in hours - one
full turn every multiple of 4.70

#local plan_moon_posr = plan_radius+plan_moon_dist+plan_moon_rdus;
#local plan_rotn = (plan_day/4.7)*-360-degrees(plan_poso);
#local plan_posx =
cos(plan_poso)*(plan_orbt_rdus+aphelion_offset*0.5)-aphelion_offset*0.5;
#local plan_posz = sin(plan_poso)*plan_orbt_rdus;

camera
 {
 location <0,1,-0.1>*(plan_moon_posr+plan_moon_rdus)*(camr_dist+1.0) look_at 0
 right x*image_width/image_height
 rotate <0,plan_rotn,0>
 translate <plan_posx,0,plan_posz>
 angle 48
 }
light_source {<-10,0.1,0> color rgb 1 photons {reflection on}}

global_settings
 {
 ambient_light 0
 max_trace_level 15
 photons {count 100000 spacing 10}
 }

#local plan_color = <0.3,0.7,1>;
union
 {
 sphere {0,plan_radius hollow texture {pigment {rgb plan_color} finish
{reflection plan_color*20}} photons {target reflection on collect off}}
 sphere {<plan_moon_posr,0,0>,plan_moon_rdus texture {pigment {rgb plan_color}}
photons {target} rotate <0,150,0>}
 translate <plan_posx,0,plan_posz>
 }

Post a reply to this message

El 01/09/11 06:40, Quartz escribió:
> My problem is that I don't want to see objects reflected in the
> surface of the planet; I only want the caustics it casts. ...Is this
> outright impossible?

   Untested solutions that come to my mind:

   1) use two planet objects: one without reflection nor photons block,
the other with reflection and photons but with a "no_image" modifier.

   2) use a two pass render: on the first pass save the photons, on the
second load the photons and get ride of the reflection on the planet finish.

   Hope this helps...

-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

Post a reply to this message

Am 01.09.2011 06:40, schrieb Quartz:
> I'm not sure if this question would be considered for "advanced" users or not,
> but: Is it possible to cast caustics from an object without seeing things
> reflected in its surface?
>
> I am modeling a planet, and I would like to see reflected light illuminating the
> dark side of one of its moons. I briefly tried radiosity, but photon mapping
> seemed more accurate.
>
> My problem is that I don't want to see objects reflected in the surface of the
> planet; I only want the caustics it casts. ...Is this outright impossible?

I don't think you'll get the proper results with photons; that approach 
assumes that the planet has a highly specular reflection profile, while 
really a planet probably should exhibit primarily diffuse reflection.

I'd suggest radiosity with a very (/really/ very) high sample count, 
setting any objects other than the planet to "no_radiosity" to avoid 
wasting intersection tests on them for the sake of radiosity sampling. 
Needs POV-Ray 3.7 though.


If you nonetheless want to go for the photons approach, try setting all 
of the objects in your scene to "no_reflection" so they don't appear in 
reflections.

Post a reply to this message

Le 2011/09/01 00:40, Quartz a écrit :
> I'm not sure if this question would be considered for "advanced" users or not,
> but: Is it possible to cast caustics from an object without seeing things
> reflected in its surface?
>
> I am modeling a planet, and I would like to see reflected light illuminating the
> dark side of one of its moons. I briefly tried radiosity, but photon mapping
> seemed more accurate.
>
> My problem is that I don't want to see objects reflected in the surface of the
> planet; I only want the caustics it casts. ...Is this outright impossible?
>

If you don't want to see the reflection of something, you add 
no_reflection to that something.

It should not affect the photons, but if your photons do cast caustics 
on that object, they won't show as the receiving surface is no longer 
visible in any reflection. A reflective object with no_reflection will 
reflect it's environment but will itself won't be reflected by other 
reflective surfaces. It will also not self reflect.

Another aproach would be to use a totaly transparent object with only 
the bright areas not transparent and having emission 1 in the finish.

In your particular case, your "solution" is not realistic.
You must NOT use both count and spacing for your photons. One OR the 
other, never both. You don't need the photons block on the light_source: 
By default all light_source emit photons that both reflect and refract 
acording to the target objects properties. It's a left over from around 
version 3.1 when photons was just begining. Exception, shadowless lights 
don't emit any photons. Your moon don't need a photons block as it don't 
reflect nor refract.

I got very good results using radiosity only.
You should make your light_source parallel.
You should NOT use ambient_lights 0.
It beter to always use assumed_gamma 1 for all scenes.
You should upgrade to version 3.7. It works much beter.




Alain

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> It should not affect the photons, but if your photons do cast caustics
> on that object, they won't show as the receiving surface is no longer
> visible in any reflection. A reflective object with no_reflection will
> reflect it's environment but will itself won't be reflected by other
> reflective surfaces. It will also not self reflect.

This doesn't appear to agree with the results that I'm getting. The
"no_reflection" approach did in fact work, although other considerations cause
me to agree that radiosity is more appropriate.

> You must NOT use both count and spacing for your photons. One OR the
> other, never both. ...

I can definitely believe I was misusing the photon feature; I'm still a newbie
with it.

> You should make your light_source parallel.

I would rather not, thanks, unless it is producing significant rounding errors
or slowing down the scene computation.

> You should NOT use ambient_lights 0.
> It beter to always use assumed_gamma 1 for all scenes.

As for ambient_light vs. assumed_gamma, it looks to me like their purposes are
totally different. An ambient_light of zero is recommended on this documentation
page for version 3.6:
http://povray.org/documentation/view/3.6.1/270/

> You should upgrade to version 3.7. It works much beter.

Upgrading to version 3.7 sounds exciting but unnecessary at this time.

Post a reply to this message

Le 2011/09/03 20:04, Quartz a écrit :
> Alain<aze### [at] qwertyorg>  wrote:
>> It should not affect the photons, but if your photons do cast caustics
>> on that object, they won't show as the receiving surface is no longer
>> visible in any reflection. A reflective object with no_reflection will
>> reflect it's environment but will itself won't be reflected by other
>> reflective surfaces. It will also not self reflect.
>
> This doesn't appear to agree with the results that I'm getting. The
> "no_reflection" approach did in fact work, although other considerations cause
> me to agree that radiosity is more appropriate.
>
>> You must NOT use both count and spacing for your photons. One OR the
>> other, never both. ...
>
> I can definitely believe I was misusing the photon feature; I'm still a newbie
> with it.

It's common isue, several users tend to use both while only one should 
be used.
There was also the isue of using reflection with a value larger than 1. 
The faint illumination on the moon was amplified 20 times causing an 
overly bright reflection.

>
>> You should make your light_source parallel.
>
> I would rather not, thanks, unless it is producing significant rounding errors
> or slowing down the scene computation.

Using parallel allow you to place the light_source representing a very 
far light much closer.
Usualy, light comming from a sun is such a case. You often end up with a 
light_source situated at over 100 000 000 units or even more when 
atempting to use real world distances, and that WILL cause problems, 
including causing the light_source to vanish.
Our Sun is at around 150000000 Km from us. In a scene scaled in m, the 
range of values is just to large to reliably compute (easily 10e10~10e12 
to 1).

>
>> You should NOT use ambient_lights 0.
>> It beter to always use assumed_gamma 1 for all scenes.
>
> As for ambient_light vs. assumed_gamma, it looks to me like their purposes are
> totally different. An ambient_light of zero is recommended on this documentation
> page for version 3.6:
> http://povray.org/documentation/view/3.6.1/270/
If you set ambient_lights 0 in a radiosity scene, you can't use high 
ambient finish as a source of illumination. Using version 3.7, you can 
use the emission finish component to have glowing objects.

ambient_lights in the global_settings purpose it to colour the ambient 
component.
It's way beter to use

#default{finish{ambient 0}}

or

add finish{ambient 0} in your textures.

assumed_gamma 1 use a linear scale allowing correct colour evaluations.

>
>> You should upgrade to version 3.7. It works much beter.
>
> Upgrading to version 3.7 sounds exciting but unnecessary at this time.

There are significant differences, many bug fixes, new features and tons 
of various improvements.
If you have a multicores processor, it will automaticaly use them all, 
for greatly improved render time. Even using a single core, it's very 
often faster than 3.6.1.
If you ever interupt a radiosity scene with 3.6.1, there will be a 
visible discontinuity. Not so with 3.7.

It's not about an exiting thing, but more about starting with a current 
version and not having to un-learn things that are no longer relevent.

>
>
>

Alain

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> There was also the isue of using reflection with a value larger than 1.

That was an intentional exaggeration for illustrative purposes.

> Using parallel allow you to place the light_source representing a very
> far light much closer.

I understand what you are saying, and often I have used parallel light sources.
In this case, call it a personal preference, since I am not using values that
high. Maybe later I will consider changing it.

> If you set ambient_lights 0 in a radiosity scene, you can't use high
> ambient finish as a source of illumination.

I don't need to in this scene. Maybe I will change my habit for my next scene,
but it doesn't matter now.

> assumed_gamma 1 use a linear scale allowing correct colour evaluations.

I am interested in being further educated on this point, but I don't have the
time right now unless it is pertinent to my question. Sorry.

> It's not about an exiting thing, but more about starting with a current
> version and not having to un-learn things that are no longer relevent.

That's what makes it exciting. But until I hear otherwise, I still see it as
unnecessary at the moment.

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
> I'd suggest radiosity with a very (/really/ very) high sample count,
> setting any objects other than the planet to "no_radiosity" to avoid
> wasting intersection tests on them for the sake of radiosity sampling.
> Needs POV-Ray 3.7 though.

Thanks a lot for your suggestions! With all of your help, I have achieved quite
satisfying results in v. 3.6.1 using radiosity by increasing the objects'
diffuse terms instead of the sample count. But I'm afraid things are about to
get a lot more complex...

The only remaining problem is, my scene includes an atmosphere around the planet
using interior & media. The moment I turn my atmosphere on, even if its diffuse,
extinction, & attenuation are all turned off and I have turned off media in the
global radiosity settings, my "caustics" disappear.

Do I need to follow your directions after all, about high sample counts in v.
3.7?

For clarity, below is my ACTUAL scene code, including the atmosphere. Apologies
for the bitmaps, which I cannot attach. The "atmos_layers" variable is used as a
kind of quality setting, since a photo-ready number of layers takes too long to
render while I'm actively working on the scene. Set it to zero to remove the
atmosphere.

--------

#local sun_radius      =   40.00; // units in megameters
#local eith_orbt_rdus  = 3000.00; // eithalica's orbit radius
#local aphelion_offset =   20.00; // distance of ephelion from
                                  // otherwise circular orbit
#local eith_radius     =    6.53; // eithalica is the planet's name
#local eith_moon_dist  =    6.00; // dist @ closest point between
                                  // eithalica's & moon's surfaces
#local eith_moon_rdus  =    6.22; // moon radius
#local eith_rotn_prod  =    4.70; // rotation period in hours
#local camr_dist       =    3.00; // multiplier for camera dist
#local eith_poso = radians(073);  // eithalica's orbital position
                                  // in radians counterclockwise
                                  // from positive x axis
#local eith_day  = (10/142)*4.70; // eith's rotational position in
                                  // hours - one full turn every
                                  // multiple of 4.70

#local atmos_color    = <5.4e-3,1.8e-2,3.6e-2>; // color that is reflected
#local atmos_twilight = 1-(1-<1.0,0.7,0.4>)*0.5; // color that is transmitted
#local atmos_layers   = 4;                      // granularity of model
#local atmos_thick    = eith_moon_dist*0.6;     // distance from planet surface
to atmosphere extremity
#local atmos_curve    = 2.5;                    // tightness of density curve
#local atmos_thresh   = 0.0;                    // density below which we won't
bother

#local eith_moon_posr = eith_radius+eith_moon_dist+eith_moon_rdus;
#local eith_rotn = (eith_day/4.7)*-360-degrees(eith_poso);
#local eith_posx =
cos(eith_poso)*(eith_orbt_rdus+aphelion_offset*0.5)-aphelion_offset*0.5;
#local eith_posz = sin(eith_poso)*eith_orbt_rdus;

camera
 {
 location <0,1,-0.1>*(eith_moon_posr+eith_moon_rdus)*(camr_dist+1.0) look_at 0
 right x*image_width/image_height
 rotate <0,eith_rotn,0>
 translate <eith_posx,0,eith_posz>
 angle 48
 }
light_source
 {
 0 color rgb 3.0
 /*looks_like
  {
  sphere
   {
   0,sun_radius
   texture {pigment {rgb 5} finish {ambient 1}}
   no_shadow
   }
  }*/
 }/*
sphere
 {
 0,1e2
 texture {pigment {rgbt <0,0,0,1>}}
 no_shadow
 hollow
 interior
  {
  media
   {
   emission <1.0e-2,5.0e-3,7.0e-4>
   intervals 1
   method 3
   samples 20
   }
  }
 }*/
sky_sphere {pigment {rgb <0,0,0>}}

global_settings
 {
 ambient_light 0
 radiosity {brightness 1.0 count 100 media off}
 max_trace_level 15
 }
#default {finish {ambient 1 diffuse 1.0}}

/*torus {eith_orbt_rdus,0.5 texture {pigment {rgb <1,0.3,0>} finish {ambient
1}}}
torus
 {
 eith_orbt_rdus,0.5 texture {pigment {rgb <1,1,0>} finish {ambient 1}}
 scale <(aphelion_offset*0.5+eith_orbt_rdus)/eith_orbt_rdus,1,1>
 translate <-aphelion_offset*0.5,0,0>
 }*/

#local eith_texture = texture
 {
 pigment {rgb <0,0,0.4>}
 finish {specular 0.7}
 normal {agate scale 1e-3}
 };
union
 {
 // eithalica
 union
  {
  sphere
   {
   0,eith_radius texture {eith_texture}
   texture {pigment {image_map {png "./eithalica_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_radius+8e-2
   texture {pigment {image_map {png "./eithalica_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  }

 // temalar
 union
  {
  sphere
   {
   0,eith_moon_rdus texture {eith_texture}
   texture {pigment {image_map {png "./temalar_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_moon_rdus+8e-2
   texture {pigment {image_map {png "./temalar_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  translate <eith_moon_posr,0,0>
  }

 // chessol
 union
  {
  sphere
   {
   0,eith_moon_rdus texture {eith_texture}
   texture {pigment {image_map {png "./chessol_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_moon_rdus+8e-2
   texture {pigment {image_map {png "./chessol_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  translate <eith_moon_posr,0,0>
  rotate <0,-120,0>
  }

 // siothum
 union
  {
  sphere
   {
   0,eith_moon_rdus texture {eith_texture}
   texture {pigment {image_map {png "./siothum_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_moon_rdus+8e-2
   texture {pigment {image_map {png "./siothum_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  translate <eith_moon_posr,0,0>
  rotate <0, 120,0>
  }
 //torus {eith_moon_posr,0.1 texture {pigment {rgb <1,1,0>} finish {ambient 1}}}

 #local loop = 1;
 #while (loop <= atmos_layers)
  #local intensity = pow(1-(loop-1)/atmos_layers,atmos_curve);
  #if (loop = 1) #local gap = -1e-8; #else #local gap = +1e-8; #end
  #if (intensity > atmos_thresh)
   difference
    {
    merge
     {
     sphere {0,eith_radius+(loop/atmos_layers)*atmos_thick}
     sphere
{<eith_moon_posr,0,0>,eith_moon_rdus+(loop/atmos_layers)*atmos_thick}
     sphere
      {
      <cos(radians( 120))*eith_moon_posr,0,sin(radians( 120))*eith_moon_posr>,
      eith_moon_rdus+(loop/atmos_layers)*atmos_thick
      }
     sphere
      {
      <cos(radians(-120))*eith_moon_posr,0,sin(radians(-120))*eith_moon_posr>,
      eith_moon_rdus+(loop/atmos_layers)*atmos_thick
      }
     }
    merge
     {
     sphere {0,eith_radius+((loop-1)/atmos_layers)*atmos_thick+gap}
     sphere
{<eith_moon_posr,0,0>,eith_moon_rdus+((loop-1)/atmos_layers)*atmos_thick+gap}
     sphere
      {
      <cos(radians( 120))*eith_moon_posr,0,sin(radians( 120))*eith_moon_posr>,
      eith_moon_rdus+((loop-1)/atmos_layers)*atmos_thick+gap
      }
     sphere
      {
      <cos(radians(-120))*eith_moon_posr,0,sin(radians(-120))*eith_moon_posr>,
      eith_moon_rdus+((loop-1)/atmos_layers)*atmos_thick+gap
      }
     }
    texture {pigment {rgbt <0,0,0,1>} finish {diffuse 0.0*intensity}}
    hollow
    interior
     {
     media
      {
      scattering {1, atmos_color*intensity extinction 0}
      //ratio 0.1 intervals 1 method 3 samples 20
      collect off
      }
     //ior 1.01
     fade_color atmos_twilight
     fade_distance eith_moon_rdus*0.085/intensity
     fade_power 10.0
     }
    }
   #end
  #local loop = loop+1;
  #end
 rotate <0,eith_rotn,0>
 translate <eith_posx,0,eith_posz>
 }

Post a reply to this message

Le 2011/09/03 21:13, Quartz a écrit :
> clipka<ano### [at] anonymousorg>  wrote:
>> I'd suggest radiosity with a very (/really/ very) high sample count,
>> setting any objects other than the planet to "no_radiosity" to avoid
>> wasting intersection tests on them for the sake of radiosity sampling.
>> Needs POV-Ray 3.7 though.
>
> Thanks a lot for your suggestions! With all of your help, I have achieved quite
> satisfying results in v. 3.6.1 using radiosity by increasing the objects'
> diffuse terms instead of the sample count. But I'm afraid things are about to
> get a lot more complex...
>
> The only remaining problem is, my scene includes an atmosphere around the planet
> using interior&  media. The moment I turn my atmosphere on, even if its diffuse,
> extinction,&  attenuation are all turned off and I have turned off media in the
> global radiosity settings, my "caustics" disappear.
>
> Do I need to follow your directions after all, about high sample counts in v.
> 3.7?
>
> For clarity, below is my ACTUAL scene code, including the atmosphere. Apologies
> for the bitmaps, which I cannot attach. The "atmos_layers" variable is used as a
> kind of quality setting, since a photo-ready number of layers takes too long to
> render while I'm actively working on the scene. Set it to zero to remove the
> atmosphere.
>
Replaced your images with pattern and colour_map having a good amount of 
transparency.

Your looks_loke is good. A looks_like object is located relative to it's 
light_source and moves with it if you change the coordinates.

Why is your sun and planets both at coordinate 0?

With 3.6.1, there was a bug in radiosity: The recursion level had to 
take transparent surfaces into consideration. You have 4 athmospheric 
layers and recursion_level default to 3. Then, you have two sets of 
layers plus the actual surface, for a total of 9.

That said, I realy think that you should use only one athmospheric shell 
containing only scattering media. You then modulate the density of that 
media as needed, using the spherical pattern scalled to the radius of 
the athmonsphre or some custom function.
You then use one or more cloud shells. Those are hollow and don't have 
their own media.

fade_power 10? for your athmosphere?
A realistic fade_power is 1 for substances to use linear fading, or 1001 
to use the exponential formula.
Test without fading gives beter results.
It's fade_power 2 for a fading light_source.

Using version 3.7RC3, the radiosity works as expected.

Keep in mind that radiosity can't illuminate your media.
media on will enable emissive media and directly illuminated scattering 
media to affect the radiosity illumination of nearby objects.



Alain

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> Why is your sun and planets both at coordinate 0?

The planet[s] should be in a union that's translated at the end.

> With 3.6.1, there was a bug in radiosity: The recursion level had to
> take transparent surfaces into consideration. You have 4 athmospheric
> layers and recursion_level default to 3. Then, you have two sets of
> layers plus the actual surface, for a total of 9.

Excellent! I think you've hit upon it, Alain! Thank you.

> That said, I realy think that you should use only one athmospheric shell
> containing only scattering media. You then modulate the density of that
> media as needed, using the spherical pattern scalled to the radius of
> the athmonsphre or some custom function.

Oh, I didn't realize we had a spherical pattern before! I will definitely
investigate.

> fade_power 10? for your athmosphere?
> A realistic fade_power is 1 for substances to use linear fading, or 1001
> to use the exponential formula.
> Test without fading gives beter results.
> It's fade_power 2 for a fading light_source.

This was to replace extinction, because I wasn't artistically satisfied with
realistic results. Still willing to work on that; I probably just didn't have it
configured correctly.

Thanks a lot, everyone! I might post more on this later, but my initial question
has been answered.

Post a reply to this message

Oh, and please note that the subject matter ("eithalica," the quadrupal planet)
is copyrighted © 2008-2011 by Peter Markley. I don't know what kinds of rules
POV-Ray has about posting copyrighted material on the newsgroup, but a thousand
thanks for your help with my scene settings.

Post a reply to this message

On 5-9-2011 1:26, Quartz wrote:
> Oh, and please note that the subject matter ("eithalica," the quadrupal planet)
> is copyrighted © 2008-2011 by Peter Markley. I don't know what kinds of rules
> POV-Ray has about posting copyrighted material on the newsgroup, but a thousand
> thanks for your help with my scene settings.
>
>
Care to elaborate a bit on "eithalica"? Cannot be found on Google... 
(just curious)

Thomas

Post a reply to this message

Le 2011/09/04 19:21, Quartz a écrit :
> Alain<aze### [at] qwertyorg>  wrote:
>> Why is your sun and planets both at coordinate 0?
>
> The planet[s] should be in a union that's translated at the end.

Then, during the devlopment phase, place your sun some distance away. 
That way, the radiosity contribution will be visible and not totaly 
hiden by the direct illumination.

>
>> With 3.6.1, there was a bug in radiosity: The recursion level had to
>> take transparent surfaces into consideration. You have 4 athmospheric
>> layers and recursion_level default to 3. Then, you have two sets of
>> layers plus the actual surface, for a total of 9.
>
> Excellent! I think you've hit upon it, Alain! Thank you.

Another reason to use version 3.7...

>
>> That said, I realy think that you should use only one athmospheric shell
>> containing only scattering media. You then modulate the density of that
>> media as needed, using the spherical pattern scalled to the radius of
>> the athmonsphre or some custom function.
>
> Oh, I didn't realize we had a spherical pattern before! I will definitely
> investigate.
>
>> fade_power 10? for your athmosphere?
>> A realistic fade_power is 1 for substances to use linear fading, or 1001
>> to use the exponential formula.
>> Test without fading gives beter results.
>> It's fade_power 2 for a fading light_source.
>
> This was to replace extinction, because I wasn't artistically satisfied with
> realistic results. Still willing to work on that; I probably just didn't have it
> configured correctly.
>
> Thanks a lot, everyone! I might post more on this later, but my initial question
> has been answered.
>
>

Just a note about the spherical pattern:
It's centered at <0,0,0>
It's value is 1 (rgb<1,1,1>) at the origin and drop to zero at a radius 
of 1, then stay to zero everywhere.

There is also the onion pattern. It's a spherical gradient pattern. 
Start at zero at the origin and climb up to 1.

In your scene, you have a merge of all your athmospheric shells 
containing a single media.
You need to give an individual shell to each planet, apply the spherical 
pattern then place them into position.
Adjust the colour_map for the pattern to be 1 at the planetary surface 
and drop to zero at the very top of the shell.
Something like:
color_map{[Planet_Radius/Athmosphere_radius rgb 1][0 rgb 0]}

It's normal to take some artistic liberties when you model something 
that is physicaly impossible. That quadruple planet just can't exist, 
the center planet may survive, but the 3 moons would be ript apart by 
the gravitational gradient and degenarate into a massive ring of 
debrits. Think Saturn's rings, but about 10000 to 1000000 times denser.



Alain

Post a reply to this message

Thomas de Groot <tenDOTlnDOTretniATtoorgedDOTt> wrote:
> On 5-9-2011 1:26, Quartz wrote:
> > Oh, and please note that the subject matter ("eithalica," the quadrupal planet)
> > is copyrighted © 2008-2011 by Peter Markley. I don't know what kinds of rules
> > POV-Ray has about posting copyrighted material on the newsgroup, but a thousand
> > thanks for your help with my scene settings.
> >
> >
> Care to elaborate a bit on "eithalica"? Cannot be found on Google...
> (just curious)
>
> Thomas

I believe it appears in the comments in my scene code, and in the filenames of
some of the bitmaps used. Other copyrighted fictional names appear in the code
also.

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> Le 2011/09/04 19:21, Quartz a écrit :
> > The planet[s] should be in a union that's translated at the end.
>
> Then, during the devlopment phase, place your sun some distance away.
> That way, the radiosity contribution will be visible and not totaly
> hiden by the direct illumination.

By "the end" I meant the end of the file or scene script, not the end of
development. The light source is very far away already, it's just also very
bright.

> Another reason to use version 3.7...

Indeed. I am hoping soon to look into what it would take to upgrade on Mac OS X
Lion.

> Just a note about the spherical pattern:
> It's centered at <0,0,0>
> It's value is 1 (rgb<1,1,1>) at the origin and drop to zero at a radius
> of 1, then stay to zero everywhere.

Thanks! So I read in the documentation.

Unfortunately, although this is very close to what I need, it won't give a
realistic exponential die-away curve like we see in earth's atmosphere:
http://en.wikipedia.org/wiki/Atmosphere_of_Earth#Pressure_and_thickness
I may need a custom function after all, but that is beyond my current
experience. I love learning new things, but it'll be a bumpy ride! ;)

> That quadruple planet just can't exist,
> the center planet may survive, but the 3 moons would be ript apart by
> the gravitational gradient and degenarate into a massive ring of
> debrits. Think Saturn's rings, but about 10000 to 1000000 times denser.

You're thinking of Roche's limit:
http://en.wikipedia.org/wiki/Roche%27s_limit

It's actually very interesting that you bring this up, because this was a
serious concern of mine when designing the planetary system. I worked out all
the physics according to my knowledge, and I think it could theoretically work.

Note that the planets make one full rotation (one day) in about 5 hours (4.70
hrs in my scene script). The system spins far, far faster than earth does, in
order to compensate for the greatly increased gravity.

When redesigning the bitmaps for the cloud layers, I'm going to have lots of fun
with the meteorological ramifications of a massively larger Coriolis effect,
among other things.

Again, this is all copyrighted by me, and thank you all so much for indulging
me! :)

Post a reply to this message

"Quartz" <qua### [at] malexmedianet> wrote:
> Thomas de Groot <tenDOTlnDOTretniATtoorgedDOTt> wrote:
> > On 5-9-2011 1:26, Quartz wrote:
> > > Oh, and please note that the subject matter ("eithalica," the quadrupal planet)
> > > is copyrighted © 2008-2011 by Peter Markley. I don't know what kinds of rules
> > > POV-Ray has about posting copyrighted material on the newsgroup, but a thousand
> > > thanks for your help with my scene settings.
> > >
> > >
> > Care to elaborate a bit on "eithalica"? Cannot be found on Google...
> > (just curious)
> >
> > Thomas
>
> I believe it appears in the comments in my scene code, and in the filenames of
> some of the bitmaps used. Other copyrighted fictional names appear in the code
> also.

I apologize, it's only copyrighted © 2011, since this is the first time I have
ever published any of it. Above, I mistakenly put the date that I invented it
and wrote it down.

Post a reply to this message

"Quartz" <qua### [at] malexmedianet> wrote:
> Indeed. I am hoping soon to look into what it would take to upgrade on Mac OS X
> Lion.

Uh-oh, looks like I'll have to compile from source if I want that to work...
Does that sound right?

Post a reply to this message

Le 2011/09/05 14:57, Quartz a écrit :

>> That quadruple planet just can't exist,
>> the center planet may survive, but the 3 moons would be ript apart by
>> the gravitational gradient and degenarate into a massive ring of
>> debrits. Think Saturn's rings, but about 10000 to 1000000 times denser.
>
> You're thinking of Roche's limit:
> http://en.wikipedia.org/wiki/Roche%27s_limit

Yes.

Anyway, those planets would be heavily distorted by the mutual 
gravitational pull.
The main planet would get strongly flatened at the poles and would 
probably show proeminent bulges toward the moons.
The moons would be ove shaped with the small end toward the main planet. 
(version 3.7 have an ove primitive)
The athmosphere can realisticaly connect all 4 worlds, allowing you to 
fly, or float, from one world to the other.

>
> It's actually very interesting that you bring this up, because this was a
> serious concern of mine when designing the planetary system. I worked out all
> the physics according to my knowledge, and I think it could theoretically work.

If the 4 planets have the same mass and density, the actual limit may be 
shorter, and the 2 oposite ones may help stabilise the third. But that 
system still looks fictional...

>
> Note that the planets make one full rotation (one day) in about 5 hours (4.70
> hrs in my scene script). The system spins far, far faster than earth does, in
> order to compensate for the greatly increased gravity.

Yep! Tidal lock between 4 bodies.

>
> When redesigning the bitmaps for the cloud layers, I'm going to have lots of fun
> with the meteorological ramifications of a massively larger Coriolis effect,
> among other things.
>
> Again, this is all copyrighted by me, and thank you all so much for indulging
> me! :)
>
>
>

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:
> Anyway, those planets would be heavily distorted by the mutual
> gravitational pull.

Yes, adding slight oblateness to the main planet and prolateness to its moons is
on my to-do list.

> The athmosphere can realisticaly connect all 4 worlds, allowing you to
> fly, or float, from one world to the other.

According to my calculations, at the surface of each planet/moon, the
acceleration due to gravity would not be too much less than on earth, in which
case the gap is far too large for a person to jump by themselves.

I'm not sure what the "escape velocity" would be though, because the gravity
falloff is greatly exaggerated from the norm by the body on the other side.
Perhaps a rocket would not be necessary.

> If the 4 planets have the same mass and density, the actual limit may be
> shorter, and the 2 oposite ones may help stabilise the third. But that
> system still looks fictional...

Of course I've never heard of NASA discovering a system like this in real life,
but I did try to be very careful in my calculations.

Would you like me to post the POV-Ray script for a simulation I did in order to
determine the free-fall acceleration in such a system?

Post a reply to this message

On 5-9-2011 21:04, Quartz wrote:
> "Quartz"<qua### [at] malexmedianet>  wrote:
> I apologize, it's only copyrighted © 2011, since this is the first time I have
> ever published any of it. Above, I mistakenly put the date that I invented it
> and wrote it down.
>
>

I see. Somewhat off topic but still curious: Do you intend to publish 
your work in some official way? Otherwise I wonder why you insist on 
copyright here. All/most scenes by all posters here are original works 
and - implicitly according to ruling etiquette - we acknowledge code 
from others when used. Or am I hopelessly naive? ;-)

Thomas

Post a reply to this message

Thomas de Groot <tenDOTlnDOTretniATtoorgedDOTt> wrote:
> On 5-9-2011 21:04, Quartz wrote:
> > "Quartz"<qua### [at] malexmedianet>  wrote:
> > I apologize, it's only copyrighted © 2011, since this is the first time I have
> > ever published any of it. Above, I mistakenly put the date that I invented it
> > and wrote it down.
> >
> >
>
> I see. Somewhat off topic but still curious: Do you intend to publish
> your work in some official way? Otherwise I wonder why you insist on
> copyright here. All/most scenes by all posters here are original works
> and - implicitly according to ruling etiquette - we acknowledge code
> from others when used. Or am I hopelessly naive? ;-)
>
> Thomas

That's great news to me! :) Sorry for being overly cautious, still a newbie to
the newsgroups. Yes, I do hope someday to syndicate works that are based on
this.

Post a reply to this message

On 6-9-2011 12:46, Quartz wrote:
>
> That's great news to me! :) Sorry for being overly cautious, still a newbie to
> the newsgroups. Yes, I do hope someday to syndicate works that are based on
> this.
>
>

You can always add a comment line to your code, stating the copyright. 
It is something I do if I make substantial parts of scenes available to 
others.

Thomas

Post a reply to this message

An interesting little system you've put together ;)

I don't think it can safely be described in terms of objects
orbiting a common center of mass: since all components are roughly
same size and same distance it is an n-body problem for n = 4.

Even ignoring that, it would be a precarious unstable balance
at best. It cannot have formed naturally, although an advanced
(and bored?) civilization might engineer and maintain it.

Post a reply to this message

Christian Froeschlin <chr### [at] chrfrde> wrote:
> An interesting little system you've put together ;)

Thank you! :)

> I don't think it can safely be described in terms of objects
> orbiting a common center of mass: since all components are roughly
> same size and same distance it is an n-body problem for n = 4.

I originally analyzed the orbit of each moon by simply adding the gravitational
forces from the other three to find its centripetal force.

> Even ignoring that, it would be a precarious unstable balance
> at best. It cannot have formed naturally, although an advanced
> (and bored?) civilization might engineer and maintain it.

Let me first grant that of course you're right; since it does not really exist,
it's fundamentally fictional, and I'm sure it still has flaws born of my own
ignorance.

However, much of the same could be said of earth - i.e. it has a precarious
balance, and it is hard to prove how it formed naturally. For some it is much
easier, in the spirit of Occam's razor, to say earth was formed supernaturally.
:)

Post a reply to this message

Thank you all again. I have incorporated a custom function to work around
POV-Ray 3.6.1's radiosity bug, and to greatly improve both the quality and the
render speed. Here is what I've settled on for now, while I render it from
various angles to get a better sense of it:

-------

// Copyright (C) 2011 by Peter Markley.

#local sun_radius      =   40.00; // units in megameters
#local eith_orbt_rdus  = 3000.00; // eithalica's orbit radius
#local aphelion_offset =   20.00; // distance of ephelion from
                                  // otherwise circular orbit
#local eith_radius     =    6.53; // eithalica is the planet's name
#local eith_mass       = 6.40e24; // units in kilograms
#local eith_moon_dist  =    6.00; // dist @ closest point between
                                  // eithalica's & moon's surfaces
#local eith_moon_rdus  =    6.22; // moon radius
#local eith_moon_mass  = 5.55e24; // moon mass
#local eith_rotn_prod  =    4.70; // rotation period in hours
#local camr_dist       =    3.00; // multiplier for camera dist
#local eith_poso = radians(073);  // eithalica's orbital position
                                  // in radians counterclockwise
                                  // from positive x axis
#local eith_day  = (10/(141+1))*4.70;//(frame_number/(final_frame+1))*4.70;
                                  // eith's rotational position in
                                  // hours - one full turn every
                                  // multiple of 4.70

#local atmos_color    = <5.4e-2,1.8e-1,3.6e-1>; // color that is reflected
//#local atmos_twilight = 1-(1-<1.0,0.7,0.4>)*1.0; // color that is transmitted

#local eith_moon_posr = eith_radius+eith_moon_dist+eith_moon_rdus;
#local eith_rotn = (eith_day/eith_rotn_prod)*-360-degrees(eith_poso);
#local eith_posx =
cos(eith_poso)*(eith_orbt_rdus+aphelion_offset*0.5)-aphelion_offset*0.5;
#local eith_posz = sin(eith_poso)*eith_orbt_rdus;

camera
 {
 location <0,1,-0.1>*(eith_moon_posr+eith_moon_rdus)*(camr_dist+1.0) look_at 0
 right x*image_width/image_height
 rotate <0,eith_rotn,0>
 translate <eith_posx,0,eith_posz>
 angle 48
 }
light_source
 {
 0 color rgb 3.0
 /*looks_like
  {
  sphere
   {
   0,sun_radius
   texture {pigment {rgb 5} finish {ambient 1}}
   no_shadow
   }
  }*/
 }/*
sphere
 {
 0,1e2
 texture {pigment {rgbt <0,0,0,1>}}
 no_shadow
 hollow
 interior
  {
  media
   {
   emission <1.0e-2,5.0e-3,7.0e-4>
   intervals 1
   method 3
   samples 20
   }
  }
 }*/
sky_sphere {pigment {rgb <0,0,0>}}

global_settings
 {
 ambient_light 1.0
 radiosity {brightness 1.0 count 100 media on recursion_limit 20}
 max_trace_level 15
 }
#default {finish {ambient 0.0 diffuse 1.0}}

/*torus {eith_orbt_rdus,0.5 texture {pigment {rgb <1,0.3,0>} finish {ambient
1}}}
torus
 {
 eith_orbt_rdus,0.5 texture {pigment {rgb <1,1,0>} finish {ambient 1}}
 scale <(aphelion_offset*0.5+eith_orbt_rdus)/eith_orbt_rdus,1,1>
 translate <-aphelion_offset*0.5,0,0>
 }*/

#local eith_texture = texture
 {
 pigment {rgb <0,0,0.4>}
 finish {specular 0.7}
 normal {agate scale 1e-3}
 };
union
 {
 // eithalica
 union
  {
  sphere
   {
   0,eith_radius texture {eith_texture}
   texture {pigment {image_map {png "./eithalica_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_radius+8e-2
   texture {pigment {image_map {png "./eithalica_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  }

 // temalar
 union
  {
  sphere
   {
   0,eith_moon_rdus texture {eith_texture}
   texture {pigment {image_map {png "./temalar_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_moon_rdus+8e-2
   texture {pigment {image_map {png "./temalar_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  translate <eith_moon_posr,0,0>
  }

 // chessol
 union
  {
  sphere
   {
   0,eith_moon_rdus texture {eith_texture}
   texture {pigment {image_map {png "./chessol_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_moon_rdus+8e-2
   texture {pigment {image_map {png "./chessol_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  translate <eith_moon_posr,0,0>
  rotate <0,-120,0>
  }

 // siothum
 union
  {
  sphere
   {
   0,eith_moon_rdus texture {eith_texture}
   texture {pigment {image_map {png "./siothum_tex.png" map_type 1}}}
   photons {target reflection on refraction off}
   }
  sphere
   {
   0,eith_moon_rdus+8e-2
   texture {pigment {image_map {png "./siothum_clouds.png" map_type 1}}}
   photons {target reflection on refraction off}
   hollow
   }
  translate <eith_moon_posr,0,0>
  rotate <0, 120,0>
  }
 //torus {eith_moon_posr,0.1 texture {pigment {rgb <1,1,0>} finish {ambient 1}}}

 #local mlef = -cos(radians(60))*eith_moon_posr;
 #local mrht = eith_moon_posr;
 #local mbot = -sin(radians(60))*eith_moon_posr;
 #local mtop = +sin(radians(60))*eith_moon_posr;
 //chessol = <left,0,top>;
 //siothum = <left,0,bottom>;
 //temalar = <right,0,0>;
 #local grav = 6.6738480e-29; // universal gravitational constant in cubic
megameters per (kilogram (seconds squared))
 #local maxi = 13e-6; // maximum expected acceleration in megameters per second
 #local mini = 7e-6; // acceleration threshold at which atmospheric density is
zero
 #local len = function(x,y,z) {sqrt(pow(x,2)+pow(y,2)+pow(z,2))}; // distance
formula

 sphere
  {
  0,eith_moon_posr+eith_moon_rdus*1.6 texture {pigment {rgbt <0,0,0,1>}}
  hollow
  interior
   {
   media
    {
    scattering {2, atmos_color extinction 1.6}
    density
     {
     average
     density_map
      {
      [0.25 function
       {
       1.0-min(1,1.0-(grav*eith_mass/pow(len(x,y,z),2)+
       grav*eith_moon_mass/pow(len(x-mlef,y-0.0,z-mtop),2)+
       grav*eith_moon_mass/pow(len(x-mlef,y-0.0,z-mbot),2)+
       grav*eith_moon_mass/pow(len(x-mrht,y-0.0,z-00.0),2)-mini)
       /(maxi-mini))
       }]
      [1.0 function
       {

(1.0-min(1,pow((sqrt(pow(x,2)+pow(y,2)+pow(z,2))-eith_radius)/(eith_radius*0.25),1/3)))+

(1.0-min(1,pow((sqrt(pow(x-mlef,2)+pow(y-0.0,2)+pow(z-mtop,2))-eith_moon_rdus)/(eith_moon_rdus*0.25),1/3)))+

(1.0-min(1,pow((sqrt(pow(x-mlef,2)+pow(y-0.0,2)+pow(z-mbot,2))-eith_moon_rdus)/(eith_moon_rdus*0.25),1/3)))+

(1.0-min(1,pow((sqrt(pow(x-mrht,2)+pow(y-0.0,2)+pow(z-00.0,2))-eith_moon_rdus)/(eith_moon_rdus*0.25),1/3)))
       }]
      }
     }
    intervals 1 method 3 samples 20
    }
   //fade_color atmos_twilight
   //fade_distance eith_moon_rdus*2.0
   //fade_power 2.0
   }
  }
 rotate <0,eith_rotn,0>
 translate <eith_posx,0,eith_posz>
 }

Post a reply to this message

"Quartz" <qua### [at] malexmedianet> wrote:
> Thomas de Groot <tenDOTlnDOTretniATtoorgedDOTt> wrote:
> > On 5-9-2011 21:04, Quartz wrote:
> > > "Quartz"<qua### [at] malexmedianet>  wrote:
> > > I apologize, it's only copyrighted © 2011, since this is the first time I have
> > > ever published any of it. Above, I mistakenly put the date that I invented it
> > > and wrote it down.
> > >
> > >
> >
> > I see. Somewhat off topic but still curious: Do you intend to publish
> > your work in some official way? Otherwise I wonder why you insist on
> > copyright here. All/most scenes by all posters here are original works
> > and - implicitly according to ruling etiquette - we acknowledge code
> > from others when used. Or am I hopelessly naive? ;-)
> >
> > Thomas
>
> That's great news to me! :) Sorry for being overly cautious, still a newbie to
> the newsgroups. Yes, I do hope someday to syndicate works that are based on
> this.

The following link is by no means a step toward syndication of real content, but
it gives a glimpse of my eventual goal.
http://youtu.be/ybbZG8cXI3A

Post a reply to this message

On 21-3-2014 19:53, Quartz wrote:
> The following link is by no means a step toward syndication of real content, but
> it gives a glimpse of my eventual goal.
> http://youtu.be/ybbZG8cXI3A
>
>
Makes one curious to see more of this :-)

Thomas

Post a reply to this message

Thomas de Groot <tho### [at] degrootorg> wrote:
> On 21-3-2014 19:53, Quartz wrote:
> > The following link is by no means a step toward syndication of real content, but
> > it gives a glimpse of my eventual goal.
> > http://youtu.be/ybbZG8cXI3A
> >
> >
> Makes one curious to see more of this :-)
>
> Thomas

I treasure this type of encouragement. Thank you!

I've just finished a rough draft of the Eithalica story, and will soon forge
ahead creating content. I'll surely keep my POV-Ray Newsgroup friends informed.
:-)

I always hate making people wait when they show appreciation for my work. ;-)

Post a reply to this message

On 5-7-2015 0:29, Quartz wrote:

> I always hate making people wait when they show appreciation for my work. ;-)
>
>

We are very patient people ;-)

-- 
Thomas

Post a reply to this message

"Quartz" <qua### [at] malexmedianet> wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> > On 21-3-2014 19:53, Quartz wrote:
> > > The following link is by no means a step toward syndication of real content, but
> > > it gives a glimpse of my eventual goal.
> > > http://youtu.be/ybbZG8cXI3A
> > >
> > >
> > Makes one curious to see more of this :-)
> >
> > Thomas
>
> I treasure this type of encouragement. Thank you!
>
> I've just finished a rough draft of the Eithalica story, and will soon forge
> ahead creating content. I'll surely keep my POV-Ray Newsgroup friends informed.
> :-)
>
> I always hate making people wait when they show appreciation for my work. ;-)

Hello again POV-Ray friends,

Thank you again for your prior encouragement. The word "soon" may have been
premature, because in 2015 I still had no peer critiques on the draft! Lack of
peer critique has no doubt spoiled the potential of countless would-be geniuses
through the ages, and I'm only grateful to be aware of it myself.

In spite of endless delays, rest assured that Eithalica is neither abandoned nor
even losing momentum. If anything (no matter how slowly) it is still gaining
momentum.

In the past 3 years I have performed two major rewrites to the story, and my
peer(s) tell me that there likely need not be a third. I am hoping to finish
editing/revising the script sometime in 2019.

Allow me also to dispel some prior vagueness. Eithalica will be an epic graphic
novel (in 3 parts as it turns out), and when the script is finished I'll
officially begin illustration.

In observance of my writing progress, I have finally polished this POV-Ray scene
to my satisfaction. It is now a participant in the CGTrader Digital Art
Competition. Voting for it at the link below is welcome but not expected (I have
no delusions that I'll win the Public award).
https://www.cgtrader.com/digital-art-competition/gallery/5853/eithalica-quadruple-planet

I have purchased the domain http://eithalica.world/ and will soon put official
information there. Admins permitting, I may still post in this newsgroup a few
more times, but I can now refer anyone interested to the proper domain.

Various lesser concept art so far can be found with the hashtag #Eithalica on
Instagram, Twitter, Facebook, and DeviantArt, as well as the current redirection
target of eithalica.world (my professional portfolio).

https://www.instagram.com/explore/tags/eithalica/
https://www.deviantart.com/tag/eithalica

A few more details:

The rewrites I mentioned have all but invalidated the YouTube video from 2015.
(I switched main characters! The previous main character is all but written
out.) The genre is still sci-fi / high fantasy, and I now have a blurb (such as
you'd find on a back cover):

>    On Eithalica, time sleeps beneath a sky of tree-leaves, and men of strange
> tongue walk with Yalengem, a race of luminescent sages.
>
>    Neither squire Lorkan nor his Yalengem friend, Niavai, know how to restore
> peace to their war-torn kingdom, or calm the ailed groaning of the forest. But
> Niavai is sure the long lost Chetnum Empire knew - by warding off the spirits
> lurking in the shadows.
>
>    When the spirits rise to snare Eithalica in living nightmares, Lorkan
> resolves to follow Niavai and recover the ancient knowledge. But their search
> becomes a pathless suffering in enemy lands on a distant moon; a titanic
> strain on Lorkan's will, and on his faith in Yalengem.

Thanks again for your help and interest! God bless.

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