[Radiance-general] Turning off specular reflections in rtrace

[Jon Sargent]

Thanks Greg,

-st 1 sounds like the trick I need, but I can't seem to get the specular
bounces to go away.  For example, if I shoot a ray (0 0 1 0 0 -1) down at a
piece of glass,

*void glass myglass 0 0 3 .5 .5 .5*
*myglass polygon srf*
*0*
*0*
*12*
*    -1 -1 0*
*    1 -1 0*
*    1 1 0*
*    -1 1 0*
*void glow myglow 0 0 4 1 1 1 0*
*myglow source ground 0 0 4 0 0 -1 180*
*myglow source sky 0 0 4 0 0 1 180*


a reflection ray bounces back, even with -st >= 1.  E.g., rtrace -oTsdV -ab
0 -st 1 gives:

ground 0.000000e+000 0.000000e+000 -1.000000e+000 4.585344e-001
4.585344e-001 4.585344e-001
sky 0.000000e+000 0.000000e+000 1.000000e+000 5.234219e-002 5.234219e-002
5.234219e-002
srf 0.000000e+000 0.000000e+000 -1.000000e+000 5.108765e-001 5.108765e-001
5.108765e-001


I see the same thing for a specular plastic BTW. Any other settings I need
to tweak?

The purpose is an annual calculation, where the direct-direct contribution
is removed from the daylight coefficients and replaced by a more accurate
calculation.  Indeed, I can write a version of the scene with the specular
properties removed (as Andy does in 5-phase), but the scene materials need
to maintain their transmissive properties, so something like glass requires
a work-around.  Maybe that's the only tricky one ... I was just trying to
see if I could rtrace-settings my way out of writing special handlers for
all the transmissive types. :)

Cheers,

Jon


On Fri, Jan 11, 2019 at 8:44 AM Greg Ward <gregoryjward at gmail.com> wrote:

> Hi Jon,
>
> It may seem counter-intuitive, but you can set the specular threshold
> (-st) to 1.0 or even higher and that should prevent specular reflections
> from being followed during rendering.  It won't be the same as not having
> that component at all, since the specular component for each surface
> (whatever it is) will be lumped in with the diffuse, instead.  Also, you
> will still see specularities from light sources.  The only way to turn that
> off is to have only glow sources in your scene.
>
> Of course, we also provide C code with Radiance, which you are welcome to
> hack.  It's designed to give physically accurate results, but you can
> rewrite it to do whatever you like.  An easier fix is to have a set of
> materials that matches the original ones but without the specular component.
>
> It might help to know the purpose of this exercise....
>
> Cheers,
> -Greg
>
> *From: *Jon Sargent <j.a.sargent at gmail.com>
>
> *Date: *January 11, 2019 8:27:38 AM PST
>
>
> Does anyone have a trick for turning off specular reflections in rtrace?
> It would be extremely helpful if there were a setting like -lr 0 that set
> the reflection limit to zero (rather than no limit).
>
> -Jon
> ____
>
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