Hello!

I am trying to make a surface composed of a multilayer. I have made an array of
bowls and I would like the light from the bottom of the bowls to reflect yellow
and the light at the sides to reflect blue, as the light incident on the bottom
hits at a normal angle and the light on the sides at 45 degrees. I have gotten
some decent result with irid (Iridescence), but not quite correct.

I was wondering if someone has perhaps written a macro or a function which would
simulate the effect of reflectance of a multilayer instead of just one thin
film?

Post a reply to this message

Matija nous illumina en ce 2009-02-09 00:28 -->
> Hello!
> 
> I am trying to make a surface composed of a multilayer. I have made an array of
> bowls and I would like the light from the bottom of the bowls to reflect yellow
> and the light at the sides to reflect blue, as the light incident on the bottom
> hits at a normal angle and the light on the sides at 45 degrees. I have gotten
> some decent result with irid (Iridescence), but not quite correct.
> 
> I was wondering if someone has perhaps written a macro or a function which would
> simulate the effect of reflectance of a multilayer instead of just one thin
> film?
> 
> 
This is not realy a "beginner" thing.

You can try it several ways.
You can use some layered textures, each one including it's own finish.
You can use several copies of the same object, varying the size by a very small 
amount. The outside one been mostly transparent, with some iridescence and 
slight reflection. This require a fairly large max_trace_level an will get 
relatively slow to realy slow.

To my knowlege, there are currently no macro or function to that purpose.

irid simulate a single film. The model is fairly simple and easy to implement.

Multiple films are another story. The end effect depends on the respective ior 
of each layer, the order of the iors, as well as ther thickness. Not all layers 
have the same thickness. The total number of layers can change.
Was the purpose of the multilayers to suppress reflection, or enhance it? For 
just a few wavelength, or a broad spectrum?


-- 
Alain
-------------------------------------------------
Why do psychics have to ask you for your name?

Post a reply to this message

Alain <ele### [at] netscapenet> wrote:
> This is not realy a "beginner" thing.
>
> You can try it several ways.
> You can use some layered textures, each one including it's own finish.
> You can use several copies of the same object, varying the size by a very small
> amount. The outside one been mostly transparent, with some iridescence and
> slight reflection. This require a fairly large max_trace_level an will get
> relatively slow to realy slow.
>
> To my knowlege, there are currently no macro or function to that purpose.
>
> irid simulate a single film. The model is fairly simple and easy to implement.
>
> Multiple films are another story. The end effect depends on the respective ior
> of each layer, the order of the iors, as well as ther thickness. Not all layers
> have the same thickness. The total number of layers can change.
> Was the purpose of the multilayers to suppress reflection, or enhance it? For
> just a few wavelength, or a broad spectrum?
>
>
> --
> Alain
> -------------------------------------------------
> Why do psychics have to ask you for your name?

Thank you very much for your answer! I am not sure how I could use layered
textures. I am guessing I would just have to divide the bowl into zones and
have the zones colored differently? Otherwise how would layering the textures
change the angle dependence? Or do you think I could actually put down many
layers with different refractive indexes and thicknesses and turn photons on?
Will POVRay actually end up calculating interference colors in this case?

Yes, that is exactly right about the multilayers. I have used free software
FreeSnell (http://people.csail.mit.edu/jaffer/FreeSnell/) to calculate the
spectra at different angles and then calculated the RGB values from there.
Would it be possible to enter a table for BRDF RGB values somewhere and
designate a finish to use that BRDF from a look-up table?

Post a reply to this message

"Matija" <nomail@nomail> wrote:
> Hello!
>
> I am trying to make a surface composed of a multilayer. I have made an array of
> bowls and I would like the light from the bottom of the bowls to reflect yellow
> and the light at the sides to reflect blue, as the light incident on the bottom
> hits at a normal angle and the light on the sides at 45 degrees. I have gotten
> some decent result with irid (Iridescence), but not quite correct.

I'm probably way off, so perhaps you shouldn't listen to me, but are you just
describing the angle of incidence pattern?  I can't find it in POV-Ray, but I
know the aoi pattern is in MegaPOV.  If you had a physical model, you could
tabulate properties by angle to get the blue/yellow transition.  Of course this
approach isn't necessarily physically-based, but it sounds similar to what
you're after.

 - Ricky

Post a reply to this message

"triple_r" <nomail@nomail> wrote:
> "Matija" <nomail@nomail> wrote:
> > Hello!
> >
> > I am trying to make a surface composed of a multilayer. I have made an array of
> > bowls and I would like the light from the bottom of the bowls to reflect yellow
> > and the light at the sides to reflect blue, as the light incident on the bottom
> > hits at a normal angle and the light on the sides at 45 degrees. I have gotten
> > some decent result with irid (Iridescence), but not quite correct.
>
> I'm probably way off, so perhaps you shouldn't listen to me, but are you just
> describing the angle of incidence pattern?  I can't find it in POV-Ray, but I
> know the aoi pattern is in MegaPOV.  If you had a physical model, you could
> tabulate properties by angle to get the blue/yellow transition.  Of course this
> approach isn't necessarily physically-based, but it sounds similar to what
> you're after.
>
>  - Ricky

I think this is what I'd need. I will look into MegaPOV. Thanks!

BTW just to illustrate better - this is what I am basing the bowl on:

http://www.nature.com/nature/journal/v404/n6777/fig_tab/404457a0_F1.html#figure-title

Matija

Post a reply to this message

Matija nous illumina en ce 2009-02-12 10:22 -->
> "triple_r" <nomail@nomail> wrote:
>> "Matija" <nomail@nomail> wrote:
>>> Hello!
>>>
>>> I am trying to make a surface composed of a multilayer. I have made an array of
>>> bowls and I would like the light from the bottom of the bowls to reflect yellow
>>> and the light at the sides to reflect blue, as the light incident on the bottom
>>> hits at a normal angle and the light on the sides at 45 degrees. I have gotten
>>> some decent result with irid (Iridescence), but not quite correct.
>> I'm probably way off, so perhaps you shouldn't listen to me, but are you just
>> describing the angle of incidence pattern?  I can't find it in POV-Ray, but I
>> know the aoi pattern is in MegaPOV.  If you had a physical model, you could
>> tabulate properties by angle to get the blue/yellow transition.  Of course this
>> approach isn't necessarily physically-based, but it sounds similar to what
>> you're after.
>>
>>  - Ricky
> 
> I think this is what I'd need. I will look into MegaPOV. Thanks!
> 
> BTW just to illustrate better - this is what I am basing the bowl on:
> 
>
http://www.nature.com/nature/journal/v404/n6777/fig_tab/404457a0_F1.html#figure-title
> 
> Matija
> 
> 
POV-Ray don't handle the polarisation of light.

-- 
Alain
-------------------------------------------------
  "Having a smoking area in a restaurant is like having a peeing area in a pool."
   --Thomas Pfeffer, American Heart Association

Post a reply to this message

> >
> >
> POV-Ray don't handle the polarisation of light.
>
> --
> Alain
> -------------------------------------------------
>   "Having a smoking area in a restaurant is like having a peeing area in a pool."
>    --Thomas Pfeffer, American Heart Association


Yeah, I have figured out as much :-) To do that kind of stuff, I would need to
use an actual simulation software (such as Meep
http://ab-initio.mit.edu/wiki/index.php/Meep). The polarization is not the key
to this
visualization, though. All that is needed is the proper color change depending
on the incident angle. I just included the link to help the good people who are
taking the time to try to visualize what I am after.

Thanks!

Matija

Post a reply to this message