perfect specular reflection in rtrace

radiance-general
1

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of
specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr 6
-lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is defined
by a diffuse material.

When I do the simulation, I get illogical results as if the specular
reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one *specular
surface*:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My *source* is described as a sun perfectly perpendicular to the surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the *sensor* is between the surface and the source and is regarding
right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular parameters)
but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

2

Hi Antoine,

Your plastic is completely black, so it won't reflect any light. You need
to set the red, green, and blue values to be positive numbers. For
instance, if you want a 50% reflective wall:

void plastic M_Spec
0
0
5 0.5 0.5 0.5 1 0

But is there a reason you're using plastic? Plastic that is 100% specular
isn't realistic, and more to the point for your use, it won't give you very
good reflections of small sources like the sun; for this, you will need to
use a mirror material.

Nathaniel

···

On Thu, Oct 12, 2017 at 10:22 AM, Antoine Bugeat <[email protected]> wrote:

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of
specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr
6 -lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is defined
by a diffuse material.

When I do the simulation, I get illogical results as if the specular
reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one *specular
surface*:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My *source* is described as a sun perfectly perpendicular to the surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the *sensor* is between the surface and the source and is regarding
right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular parameters)
but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

_______________________________________________
Radiance-general mailing list
[email protected]
https://www.radiance-online.org/mailman/listinfo/radiance-general

3

Antoine

If you want to have the specular component considered in your numerical
calculations you have to use a different material type, perhaps even
'mirror'. IIRC the specular part in plastic is purely aesthetic but is not
taken into account for numeric calculations.

Regards,
Thomas

···

On Thu, Oct 12, 2017 at 12:22 PM, Antoine Bugeat <[email protected]> wrote:

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of
specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr
6 -lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is defined
by a diffuse material.

When I do the simulation, I get illogical results as if the specular
reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one *specular
surface*:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My *source* is described as a sun perfectly perpendicular to the surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the *sensor* is between the surface and the source and is regarding
right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular parameters)
but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

_______________________________________________
Radiance-general mailing list
[email protected]
https://www.radiance-online.org/mailman/listinfo/radiance-general

4

Hi Antoine,

It seems you are running up against the limitation of ray-tracing to find small sources such as the sun in specular surfaces.

There is a specific fix for this problem for flat surface in Radiance, which is the "virtual source" calculation. However, you need to use a special "mirror" type rather than "plastic" to enable this:

void mirror M_Spec
0
0
3 1 1 1

If you use this as your material, I think you will get the results you expect.

I should point out that a 100% specular material is not realistic. Polished metallic surfaces may reflect as much as 99% of light, but 100% is difficult to achieve without resorting to a prismatic dielectric film or similar.

Best,
-Greg

···

From: Antoine Bugeat <[email protected]>
Date: October 12, 2017 10:22:28 AM PDT

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr 6 -lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is defined by a diffuse material.

When I do the simulation, I get illogical results as if the specular reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one specular surface:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
  -5.0 0.0 5.0
  5.0 0.0 5.0
  5.0 0.0 -5.0

My source is described as a sun perfectly perpendicular to the surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the sensor is between the surface and the source and is regarding right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular parameters) but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat
https://www.radiance-online.org/mailman/listinfo/radiance-general

5

Hi Antoine,
specular reflections are not traced at all to light sources in the ambient calculation (which you invoke by -I). Only to glow material. Thats why also the reflections of the sun on glass-material is not captured by rtrace -I.
So either you use mirror material and a -dr >2 or you calculate a 180degree fisheye on you point and calculate the illuminace from the image. The view rays for the image are traced via specular surfaces towards light sources.
Jan

···

On 12 October 2017 19:22:28 CEST, Antoine Bugeat <[email protected]> wrote:

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of
specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM
uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512
-lr 6
-lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is
defined
by a diffuse material.

When I do the simulation, I get illogical results as if the specular
reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one *specular
surface*:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My *source* is described as a sun perfectly perpendicular to the
surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the *sensor* is between the surface and the source and is regarding
right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular
parameters)
but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

--
Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail gesendet.

6

Hello all,

First, thank you very much for your quick answers.

If I understand correctly, among the possible options for solving my
problem, the simplest is to replace the perfect specular "plastic" by a
"mirror" material to have a "virtual source" calculation (I agree that 100%
of reflection is totally not real but it's just for this case to understand
the calculation).

void mirror M_Spec
0
0
3 1 1 1

But I still get 0...

As a reminder, I use these radiance parameters (the same as DAYSIM except
that I increase the -dr):
-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr 6
-lw 0.004 -st 0.1 -oov

In parallel, I found a paper written by Roland Schregle (Lucerne University
2015) with an extension of Radiance about photon mapping for caustics
reflection. It looks pretty complex and I think (and I hope) that I can
solve my problem without using this.

Best Regards,

Antoine

···

2017-10-12 22:45 GMT+02:00 Jan Wienold <[email protected]>:

Hi Antoine,
specular reflections are not traced at all to light sources in the ambient
calculation (which you invoke by -I). Only to glow material. Thats why also
the reflections of the sun on glass-material is not captured by rtrace -I.
So either you use mirror material and a -dr >2 or you calculate a
180degree fisheye on you point and calculate the illuminace from the image.
The view rays for the image are traced via specular surfaces towards light
sources.
Jan

On 12 October 2017 19:22:28 CEST, Antoine Bugeat <[email protected]> > wrote:

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of
specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512
-lr 6 -lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is
defined by a diffuse material.

When I do the simulation, I get illogical results as if the specular
reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one *specular
surface*:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My *source* is described as a sun perfectly perpendicular to the surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the *sensor* is between the surface and the source and is regarding
right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular
parameters) but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

--
Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail
gesendet.

_______________________________________________
Radiance-general mailing list
[email protected]
https://www.radiance-online.org/mailman/listinfo/radiance-general

7

Hi Antoine,

Using the mirror material should work, but I forgot to mention that it's a one-sided effect. You need to be looking at the front of your surface rather than the backside, which means the vertices need to be ordered counter-clockwise from the side you're looking at.

I didn't check initially, but the surface is the wrong way around from your selected evaluation point. Your sun is also on the wrong side. If you reverse the order of your polygon vertices, then it should work as expected.

The photon-mapping approach, which is now built into Radiance, should also work. It is a more complex solution, but necessary when the reflecting surfaces are curved.

Cheers,
-Greg

···

From: Antoine Bugeat <[email protected]>
Date: October 13, 2017 8:02:20 AM PDT

Hello all,

First, thank you very much for your quick answers.

If I understand correctly, among the possible options for solving my problem, the simplest is to replace the perfect specular "plastic" by a "mirror" material to have a "virtual source" calculation (I agree that 100% of reflection is totally not real but it's just for this case to understand the calculation).

void mirror M_Spec
0
0
3 1 1 1

But I still get 0...

As a reminder, I use these radiance parameters (the same as DAYSIM except that I increase the -dr):
-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr 6 -lw 0.004 -st 0.1 -oov

In parallel, I found a paper written by Roland Schregle (Lucerne University 2015) with an extension of Radiance about photon mapping for caustics reflection. It looks pretty complex and I think (and I hope) that I can solve my problem without using this.

Best Regards,

Antoine

2017-10-12 22:45 GMT+02:00 Jan Wienold <[email protected]>:
Hi Antoine,
specular reflections are not traced at all to light sources in the ambient calculation (which you invoke by -I). Only to glow material. Thats why also the reflections of the sun on glass-material is not captured by rtrace -I.
So either you use mirror material and a -dr >2 or you calculate a 180degree fisheye on you point and calculate the illuminace from the image. The view rays for the image are traced via specular surfaces towards light sources.
Jan

On 12 October 2017 19:22:28 CEST, Antoine Bugeat <[email protected]> wrote:
Hello all,

I'm a civil engineering student and I'm trying to compute the impact of specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr 6 -lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is defined by a diffuse material.

When I do the simulation, I get illogical results as if the specular reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one specular surface:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My source is described as a sun perfectly perpendicular to the surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the sensor is between the surface and the source and is regarding right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular parameters) but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

8

Hello all,

Thanks again for your quick reply. Now I can model my street walls as a
perfect specular materials ("mirror" materials) and obtain the results I
expected.

I come back with an other problem:

The main purpose of my work is to compute the impact of the specular
reflections in a street canyon.
So, I would like to separate the light that comes from the reflections of
the walls (only specular) and the light that comes directly from the sky
(defined by "glow" material and "skyfunc"). I wanted to do a simulation
with 0 reflection and an other simulation with 5 (or more) reflections. The
results obtain with 0 reflection is directly the direct sky component and
the substraction of 5 reflections - 0 reflections is the "environment" part.

I did the same process with a diffuse environment and it worked well. I
changed the -ab parameter:
-ab 1 to have the direct sky component (1 because of "glow" material);
and -ab 5 to have the entire reflections in the environment.

*But in the specular environment (with "mirror" wall) there is no
difference between my "0 reflection" case and my "5 reflections" case*
I tried to change the parameters -ab -dr and -lr and it seems that all the
reflections is computed whatever the parameters.

From what I know, -ab is for "diffuse inter-reflections", -dr is for

"direct reflections", and -lr I don't know...

Obviously, I can replace the "0 reflection specular" case with the "0
refelction diffuse" case because it should be exactly the same, but I would
like to understand where this problem comes from.

I do not know if I was clear and precise in my explanation. I am available
if you have questions.

Regards,

Antoine

···

2017-10-13 19:04 GMT+02:00 Greg Ward <[email protected]>:

Hi Antoine,

Using the mirror material should work, but I forgot to mention that it's a
one-sided effect. You need to be looking at the front of your surface
rather than the backside, which means the vertices need to be ordered
counter-clockwise from the side you're looking at.

I didn't check initially, but the surface is the wrong way around from
your selected evaluation point. Your sun is also on the wrong side. If
you reverse the order of your polygon vertices, then it should work as
expected.

The photon-mapping approach, which is now built into Radiance, should also
work. It is a more complex solution, but necessary when the reflecting
surfaces are curved.

Cheers,
-Greg

*From: *Antoine Bugeat <[email protected]>

*Date: *October 13, 2017 8:02:20 AM PDT

Hello all,

First, thank you very much for your quick answers.

If I understand correctly, among the possible options for solving my
problem, the simplest is to replace the perfect specular "plastic" by a
"mirror" material to have a "virtual source" calculation (I agree that 100%
of reflection is totally not real but it's just for this case to understand
the calculation).

void mirror M_Spec
0
0
3 1 1 1

But I still get 0...

As a reminder, I use these radiance parameters (the same as DAYSIM except
that I increase the -dr):
-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512 -lr 6
-lw 0.004 -st 0.1 -oov

In parallel, I found a paper written by Roland Schregle (Lucerne
University 2015) with an extension of Radiance about photon mapping for
caustics reflection. It looks pretty complex and I think (and I hope) that
I can solve my problem without using this.

Best Regards,

Antoine

2017-10-12 22:45 GMT+02:00 Jan Wienold <[email protected]>:

Hi Antoine,
specular reflections are not traced at all to light sources in the
ambient calculation (which you invoke by -I). Only to glow material. Thats
why also the reflections of the sun on glass-material is not captured by
rtrace -I.
So either you use mirror material and a -dr >2 or you calculate a
180degree fisheye on you point and calculate the illuminace from the image.
The view rays for the image are traced via specular surfaces towards light
sources.
Jan

On 12 October 2017 19:22:28 CEST, Antoine Bugeat <[email protected]> >> wrote:

Hello all,

I'm a civil engineering student and I'm trying to compute the impact of
specular reflections in a street "canyon".
My problem is:
I use rtrace function with the basic parameters, the same as DAYSIM uses
(-I -aa 0.1 -ab 5 -ad 1000 -ar 300 -as 20 -dj 0 -dr 5 -ds 0.2 -dp 512
-lr 6 -lw 0.004 -st 0.1 -oov)
My sky and sun description come from gendaylit.
My wall is defined by a perfect specular plastic and the ground is
defined by a diffuse material.

When I do the simulation, I get illogical results as if the specular
reflection of the walls had no impact.

So, I tried to simulate a really simple scene with only one *specular
surface*:

void plastic M_Spec
0
0
5 0 0 0 1 0

M_Spec polygon 1
0
0
12 -5.0 0.0 -5.0
-5.0 0.0 5.0
5.0 0.0 5.0
5.0 0.0 -5.0

My *source* is described as a sun perfectly perpendicular to the
surface:

void light solar
0
0
3 1000 1000 1000

solar source sun
0
0
4 0.0 -1.0 0.0 0.5

And the *sensor* is between the surface and the source and is regarding
right to the surface:

0.0 -5.0 0.0 0.0 1.0 0.0

And in this case, I get 0 after my rtrace simulation.
I tried to vary some parameters of rtrace (direct and specular
parameters) but it change nothing I still get 0.

Thank you for your help.

Antoine Bugeat

_______________________________________________
Radiance-general mailing list
[email protected]
https://www.radiance-online.org/mailman/listinfo/radiance-general

9

Hi Antoine,

Glad you got the basic mirror type working.

One thing you should take into consideration for your model is the Fresnel factor that affects how light reflects off glazing materials (building facades). The "mirror" type does not change its reflectance with angle, but coated and uncoated glazing materials do. There are exact calculations and approximations you can use, which you can apply as a "brightfunc" modifier to the "mirror" type.

To answer your question, though, the number of reflections or redirections from virtual source materials is controlled by the -dr rendering option. Set this to "-dr 0" if you do not wish to include any specular source redirections. You will still get reflections (even multiple reflections) of the sky, even if you set -ab 0. That's because the specular reflections don't count in the diffuse interreflection (ambient) calculation. To fully eliminate sky reflections, you'll need to set -lr 0.

Cheers,
-Greg

···

From: Antoine Bugeat <[email protected]>
Date: October 24, 2017 10:38:57 AM PDT

Hello all,

Thanks again for your quick reply. Now I can model my street walls as a perfect specular materials ("mirror" materials) and obtain the results I expected.

I come back with an other problem:

The main purpose of my work is to compute the impact of the specular reflections in a street canyon.
So, I would like to separate the light that comes from the reflections of the walls (only specular) and the light that comes directly from the sky (defined by "glow" material and "skyfunc"). I wanted to do a simulation with 0 reflection and an other simulation with 5 (or more) reflections. The results obtain with 0 reflection is directly the direct sky component and the substraction of 5 reflections - 0 reflections is the "environment" part.

I did the same process with a diffuse environment and it worked well. I changed the -ab parameter:
-ab 1 to have the direct sky component (1 because of "glow" material);
and -ab 5 to have the entire reflections in the environment.

But in the specular environment (with "mirror" wall) there is no difference between my "0 reflection" case and my "5 reflections" case
I tried to change the parameters -ab -dr and -lr and it seems that all the reflections is computed whatever the parameters.
From what I know, -ab is for "diffuse inter-reflections", -dr is for "direct reflections", and -lr I don't know...

Obviously, I can replace the "0 reflection specular" case with the "0 refelction diffuse" case because it should be exactly the same, but I would like to understand where this problem comes from.

I do not know if I was clear and precise in my explanation. I am available if you have questions.

Regards,

Antoine

10

Hello

Thanks again for your help Greg

I still have not been able to solve my problem ...

To summarize my case, I have an environment composed only of surface
"mirror" and a light source "glow" (the sky). I want to get only the
radiation that comes directly from the source without any reflection.
It seems that even with the parameters -ab 1 -dr 0 -lr 0 (-ab 1 because the
sky is modeled with "glow") the radiation coming from the sky produces
reflections in the scene.

I modeled the environment with the material "plastic" and it works
perfectly. I'm almost sure that the problem comes from the material "glow"
combined with materials "mirror" but I want to keep this configuration.

Regards,

Antoine

···

2017-10-24 20:46 GMT+02:00 Greg Ward <[email protected]>:

Hi Antoine,

Glad you got the basic mirror type working.

One thing you should take into consideration for your model is the Fresnel
factor that affects how light reflects off glazing materials (building
facades). The "mirror" type does not change its reflectance with angle,
but coated and uncoated glazing materials do. There are exact calculations
and approximations you can use, which you can apply as a "brightfunc"
modifier to the "mirror" type.

To answer your question, though, the number of reflections or redirections
from virtual source materials is controlled by the -dr rendering option.
Set this to "-dr 0" if you do not wish to include any specular source
redirections. You will still get reflections (even multiple reflections)
of the sky, even if you set -ab 0. That's because the specular reflections
don't count in the diffuse interreflection (ambient) calculation. To fully
eliminate sky reflections, you'll need to set -lr 0.

Cheers,
-Greg

*From: *Antoine Bugeat <[email protected]>

*Date: *October 24, 2017 10:38:57 AM PDT

Hello all,

Thanks again for your quick reply. Now I can model my street walls as a
perfect specular materials ("mirror" materials) and obtain the results I
expected.

I come back with an other problem:

The main purpose of my work is to compute the impact of the specular
reflections in a street canyon.
So, I would like to separate the light that comes from the reflections of
the walls (only specular) and the light that comes directly from the sky
(defined by "glow" material and "skyfunc"). I wanted to do a simulation
with 0 reflection and an other simulation with 5 (or more) reflections. The
results obtain with 0 reflection is directly the direct sky component and
the substraction of 5 reflections - 0 reflections is the "environment" part.

I did the same process with a diffuse environment and it worked well. I
changed the -ab parameter:
-ab 1 to have the direct sky component (1 because of "glow" material);
and -ab 5 to have the entire reflections in the environment.

*But in the specular environment (with "mirror" wall) there is no
difference between my "0 reflection" case and my "5 reflections" case*
I tried to change the parameters -ab -dr and -lr and it seems that all the
reflections is computed whatever the parameters.
From what I know, -ab is for "diffuse inter-reflections", -dr is for
"direct reflections", and -lr I don't know...

Obviously, I can replace the "0 reflection specular" case with the "0
refelction diffuse" case because it should be exactly the same, but I would
like to understand where this problem comes from.

I do not know if I was clear and precise in my explanation. I am available
if you have questions.

Regards,

Antoine

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Hi Antoine,

The "-lr 0" doesn't mean "zero reflections," but "no limit on reflections," so that's part of your problem. Setting "-dr 0" has no effect if you don't have any non-glow light sources. Offhand, I don't know how to compute what you're after other than temporarily replacing your mirror with a completely black surface.

Cheers,
-Greg

···

From: Antoine Bugeat <[email protected]>
Date: November 27, 2017 8:58:19 AM PST

Hello

Thanks again for your help Greg

I still have not been able to solve my problem ...

To summarize my case, I have an environment composed only of surface "mirror" and a light source "glow" (the sky). I want to get only the radiation that comes directly from the source without any reflection.
It seems that even with the parameters -ab 1 -dr 0 -lr 0 (-ab 1 because the sky is modeled with "glow") the radiation coming from the sky produces reflections in the scene.

I modeled the environment with the material "plastic" and it works perfectly. I'm almost sure that the problem comes from the material "glow" combined with materials "mirror" but I want to keep this configuration.

Regards,

Antoine

2017-10-24 20:46 GMT+02:00 Greg Ward <[email protected]>:
Hi Antoine,

Glad you got the basic mirror type working.

One thing you should take into consideration for your model is the Fresnel factor that affects how light reflects off glazing materials (building facades). The "mirror" type does not change its reflectance with angle, but coated and uncoated glazing materials do. There are exact calculations and approximations you can use, which you can apply as a "brightfunc" modifier to the "mirror" type.

To answer your question, though, the number of reflections or redirections from virtual source materials is controlled by the -dr rendering option. Set this to "-dr 0" if you do not wish to include any specular source redirections. You will still get reflections (even multiple reflections) of the sky, even if you set -ab 0. That's because the specular reflections don't count in the diffuse interreflection (ambient) calculation. To fully eliminate sky reflections, you'll need to set -lr 0.

Cheers,
-Greg

From: Antoine Bugeat <[email protected]>
Date: October 24, 2017 10:38:57 AM PDT

Hello all,

Thanks again for your quick reply. Now I can model my street walls as a perfect specular materials ("mirror" materials) and obtain the results I expected.

I come back with an other problem:

The main purpose of my work is to compute the impact of the specular reflections in a street canyon.
So, I would like to separate the light that comes from the reflections of the walls (only specular) and the light that comes directly from the sky (defined by "glow" material and "skyfunc"). I wanted to do a simulation with 0 reflection and an other simulation with 5 (or more) reflections. The results obtain with 0 reflection is directly the direct sky component and the substraction of 5 reflections - 0 reflections is the "environment" part.

I did the same process with a diffuse environment and it worked well. I changed the -ab parameter:
-ab 1 to have the direct sky component (1 because of "glow" material);
and -ab 5 to have the entire reflections in the environment.

But in the specular environment (with "mirror" wall) there is no difference between my "0 reflection" case and my "5 reflections" case
I tried to change the parameters -ab -dr and -lr and it seems that all the reflections is computed whatever the parameters.
From what I know, -ab is for "diffuse inter-reflections", -dr is for "direct reflections", and -lr I don't know...

Obviously, I can replace the "0 reflection specular" case with the "0 refelction diffuse" case because it should be exactly the same, but I would like to understand where this problem comes from.

I do not know if I was clear and precise in my explanation. I am available if you have questions.

Regards,

Antoine