Hello everybody,
I have measured a surface of metal with a topographical instrument. Hence my
surface is composed of many micro facet.
My goal is to study the surfacic diffusion of light onto this surface (like
the gloss...). I need to make physically realistic simulation.
My problem is to set the finish of my object to fullfill my objectif.

Do you have any idea of howw I should proceed?
I join what i tried:
/////
 finish{

        diffuse 0
        ambient 0
        conserve_energy
  reflection {
    0.0, 1.0
    fresnel on

}
specular 1

}

       interior{ior 1.5}
/////

Thanks by advance
pierre

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pierre nous apporta ses lumieres en ce 7 / 05 / 2007 04:10:
> Hello everybody,
> I have measured a surface of metal with a topographical instrument. Hence my
> surface is composed of many micro facet.
> My goal is to study the surfacic diffusion of light onto this surface (like
> the gloss...). I need to make physically realistic simulation.
> My problem is to set the finish of my object to fullfill my objectif.
> 
> Do you have any idea of howw I should proceed?
> I join what i tried:
> /////
>  finish{
> 
>         diffuse 0
>         ambient 0
>         conserve_energy
>   reflection {
>     0.0, 1.0
>     fresnel on
> 
> }
> specular 1
> 
> }
> 
>        interior{ior 1.5}
> /////
> 
> Thanks by advance
> pierre
> 
> 
Use your collected data into a mesh or use it to generate a height_field.
A metal don't have an index of reflection, or can be assumed to have a very, 
very large one. If you use it and fresnel on, it simulate a glazed, oily, or 
varnished surface.
Usualy, a metalic surface reflectivity is mostly constant, using reflection{0,1} 
you deffine a surface that don't reflect light comming in a perpendicular 
direction, and reflect totaly at grazing incidence. Beter to use a constant 
reflection 0.9. (use a value between 0.7, slightly mate, and 0.95, highly polished)
The specular keyword is used to simulate the surface diffusion of light from a 
source of illumination. phong do the same, but using a slightly different algotythm.

-- 
Alain
-------------------------------------------------
HAMMER:  Originally employed as a weapon of war, the hammer nowadays is used as 
a kind of divining rod to locate expensive bike parts not far from the object we 
are trying to hit.

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Hi Alain,

thanks for your answer.
My data are stored in a mesh.
According to what you said if I change the ior from 1.5 into 4.8 (refractive
index of iron), things should go well?
It is pretty hard from the tutorial(s) to isolates the parameters permetting
to simulate behaviour according to the law of geometrical optics...
pierre



Alain <ele### [at] netscapenet> wrote:
> pierre nous apporta ses lumieres en ce 7 / 05 / 2007 04:10:
> > Hello everybody,
> > I have measured a surface of metal with a topographical instrument. Hence my
> > surface is composed of many micro facet.
> > My goal is to study the surfacic diffusion of light onto this surface (like
> > the gloss...). I need to make physically realistic simulation.
> > My problem is to set the finish of my object to fullfill my objectif.
> >
> > Do you have any idea of howw I should proceed?
> > I join what i tried:
> > /////
> >  finish{
> >
> >         diffuse 0
> >         ambient 0
> >         conserve_energy
> >   reflection {
> >     0.0, 1.0
> >     fresnel on
> >
> > }
> > specular 1
> >
> > }
> >
> >        interior{ior 1.5}
> > /////
> >
> > Thanks by advance
> > pierre
> >
> >
> Use your collected data into a mesh or use it to generate a height_field.
> A metal don't have an index of reflection, or can be assumed to have a very,
> very large one. If you use it and fresnel on, it simulate a glazed, oily, or
> varnished surface.
> Usualy, a metalic surface reflectivity is mostly constant, using reflection{0,1}
> you deffine a surface that don't reflect light comming in a perpendicular
> direction, and reflect totaly at grazing incidence. Beter to use a constant
> reflection 0.9. (use a value between 0.7, slightly mate, and 0.95, highly polished)
> The specular keyword is used to simulate the surface diffusion of light from a
> source of illumination. phong do the same, but using a slightly different algotythm.
>
> --
> Alain
> -------------------------------------------------
> HAMMER:  Originally employed as a weapon of war, the hammer nowadays is used as
> a kind of divining rod to locate expensive bike parts not far from the object we
> are trying to hit.

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> My data are stored in a mesh.
> According to what you said if I change the ior from 1.5 into 4.8 
> (refractive
> index of iron), things should go well?
> It is pretty hard from the tutorial(s) to isolates the parameters 
> permetting
> to simulate behaviour according to the law of geometrical optics...
> pierre
>

POV doesn't simulate real life physics.
In general, POV handles reflection in the finish statement,
something like...

texture { pigment{rgb <0.5,0.5,0.5>}
   finish{ reflection {
         1,1
         metallic
         fresnel on }
   }
}

The normals of a mesh can make an object look very faceted,
you can get around this by using smooth_triangles in your mesh.

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