Shadow above highlight?

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into my room.

I am using the following gensky to attempt to only light the room using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
0
4 0 0 0 0

sky_glow source sky
0
0
4 0 0 1 180

This picture was rendered using -ab 1

You'll note on this image, that there is a strange shadow on the ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the "back" of
the box, with the light on the ceiling instead of the floor. There is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpgThis picture was rendered using -ab 0

Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not causing
the shadow, instead the highlight on the floor causes the shadow on the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into my room.

[...]

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg
You'll note on this image, that there is a strange shadow on the ceiling.
I am unable to figure out why.

John. I can't really explain what's going on but have you tried to
increase your "-ab" value? This should provide you with a more
even light distribution.

You can probably also change other values like "-ad" or "-aa".
But you didn't comment on those so I can't say if there is potential.

Thomas

···

On Mon, Jul 27, 2009 at 11:41 PM, <[email protected]> wrote:

Hi John,

As Thomas mentioned it might be helpful to post the parameters that you used to produce the image. Also to be clear, if you "only" want sunlight (no sky) then you should only use the gensky line, removing:

skyfunc glow sky_glow
0
4 0 0 0 0

sky_glow source sky
0
4 0 0 1 180

These lines produce a sky description to go along with the sun (and skyfunc definition) produced by gensky.

-Jack

Thomas Bleicher wrote:

···

On Mon, Jul 27, 2009 at 11:41 PM, <[email protected]> wrote:
  

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into my room.
    
[...]

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg
You'll note on this image, that there is a strange shadow on the ceiling.
I am unable to figure out why.
    
John. I can't really explain what's going on but have you tried to
increase your "-ab" value? This should provide you with a more
even light distribution.

You can probably also change other values like "-ad" or "-aa".
But you didn't comment on those so I can't say if there is potential.

Thomas

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
  
--
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

Hi John,

Since Radiance uses an azimuth/altitude breakup of the hemisphere, odd things can happen at the zenith in the indirect calculation, which is why it's generally good to have a "direct" calculation as well. You can eliminate this problem by changing your window to an illum via mkillum or even applying the sky distribution function to the window directly as demonstrated on page 32 of the introductory chapter of RwR:

  http://radsite.lbl.gov/radiance/book/ch1/ch1.pdf

You might also try setting -aa 0, which would avoid indirect interpolation and perhaps help matters by itself (though it will take longer).

Best,
-Greg

···

From: [email protected]
Date: July 27, 2009 3:41:40 PM PDT

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into my room.

I am using the following gensky to attempt to only light the room using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
4 0 0 0 0

sky_glow source sky
0
4 0 0 1 180

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg
You'll note on this image, that there is a strange shadow on the ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the "back" of
the box, with the light on the ceiling instead of the floor. There is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpgThis picture was rendered using -ab 0

Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not causing
the shadow, instead the highlight on the floor causes the shadow on the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

These images are done using variations on:

rpict -bv- -ab 1 -dp 8192 -ar 256 -ms 0.033 -ds .07 -dt .05 -dc .75 -dr 3
-sj 1 -vf 0.vf -st .01 -aa .01 -ad 4096 -as 1024 -lr 24 -lw .0002

The reason I am only using -ab 1 instead of a higher number, is that I
originally started with a higher number when I noticed the strange
behavior. I figured if I could fix it on 1 bounce, that would fix it for
all higher bounces (and is faster to test). This is probably higher
settings than necessary for a decent output, but this shouldn't cause the
error to my knowledge.

==============Original message text===============

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into my room.

[...]

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg> You'll note on this image, that there is a strange shadow on the ceiling.
I am unable to figure out why.

John. I can't really explain what's going on but have you tried to
increase your "-ab" value? This should provide you with a more
even light distribution.

You can probably also change other values like "-ad" or "-aa".
But you didn't comment on those so I can't say if there is potential.

Thomas

===========End of original message text===========

···

On Mon, 27 Jul 2009 19:03:31 EDT Thomas Bleicher wrote:
On Mon, Jul 27, 2009 at 11:41 PM, <[email protected]> wrote:

Hmm, well no suggestions thus far has helped solve the problem I am
having. I think it would help if I explain what I am trying to do. I am
attempting to validate radiosity calculations against a raytracer (in
this case Radiance). I am doing this with a simple example of a box lit
only by direct sun and ambient bounces, so there is no sky distribution.

I have attempted many different rendering options, such as -aa 0 and many
other "high quality" level options as recommended in the Rendering with
Radiance book. These do not get rid of the problem. As you can see in my
gensky below, the sun shouldn't be approaching the zenith, as it has been
revealed can cause problems.

I was reccommended to try using mkillum to turn the window into an illum
surface. I have attempted this, but it doesn't appear to do anything, so
I could be using it incorrectly? I am only using a single ambient bounce
in my calculations because the shadow is still there even on higher
amounts, such as -ab 20. I decided -ab 1 would make it easier to track
down the problem as well as take less computation time.

Any more thoughts on what could be causing this? Could it be a problem
with gensky similar to the zenith problem maybe?

--John Schwartz

From: [email protected]
Date: July 27, 2009 3:41:40 PM PDT

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into
my room.

I am using the following gensky to attempt to only light the room
using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
0
4 0 0 0 0

sky_glow source sky
0
0
4 0 0 1 180

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg> You'll note on this image, that there is a strange shadow on the > ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the
"back" of
the box, with the light on the ceiling instead of the floor. There
is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpg This > picture was rendered using -ab 0>
Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not causing
the shadow, instead the highlight on the floor causes the shadow on
the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

===========End of original message text===========

===========End of original message text===========

Can you send me your scene description, so I can have a look at it? This is the worst possible timing for me, but you're going to get nowhere unless you share your scene files. It's impossible to deduce what's going wrong from an image.

-Greg

···

From: [email protected]
Date: August 13, 2009 1:42:40 PM PDT

Hmm, well no suggestions thus far has helped solve the problem I am
having. I think it would help if I explain what I am trying to do. I am
attempting to validate radiosity calculations against a raytracer (in
this case Radiance). I am doing this with a simple example of a box lit
only by direct sun and ambient bounces, so there is no sky distribution.

I have attempted many different rendering options, such as -aa 0 and many
other "high quality" level options as recommended in the Rendering with
Radiance book. These do not get rid of the problem. As you can see in my
gensky below, the sun shouldn't be approaching the zenith, as it has been
revealed can cause problems.

I was reccommended to try using mkillum to turn the window into an illum
surface. I have attempted this, but it doesn't appear to do anything, so
I could be using it incorrectly? I am only using a single ambient bounce
in my calculations because the shadow is still there even on higher
amounts, such as -ab 20. I decided -ab 1 would make it easier to track
down the problem as well as take less computation time.

Any more thoughts on what could be causing this? Could it be a problem
with gensky similar to the zenith problem maybe?

--John Schwartz

From: [email protected]
Date: July 27, 2009 3:41:40 PM PDT

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into
my room.

I am using the following gensky to attempt to only light the room
using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
4 0 0 0 0

sky_glow source sky
0
4 0 0 1 180

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg> You'll note on this image, that there is a strange shadow on the > ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the
"back" of
the box, with the light on the ceiling instead of the floor. There
is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpg This > picture was rendered using -ab 0>
Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not causing
the shadow, instead the highlight on the floor causes the shadow on
the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

John,

I'd also like to see your scene, but while I wait I'll go out on a limb:
AFAIK in radiance, an ambient sample ray is never emitted normal to a
surface. I suspect your shadow results from the (slightly) decreased
probability of sampling the highlight from the area directly above the
highlight. This effect can be compounded by the -as setting (which never
samples the upper edge of a division, but can sample the lower edge of a
division).

My suggestion: try a high ad value coupled with no ambient super samples.
-ad 20000 -as 0

As far as your comparison between raytracing and radiosity, You pick a scene
that plays to all the strengths of radiosity. Radiosity with a dense mesh
produces a highly accurate result in relatively little time for scenes that
have very simple geometry and are limited to completely diffuse reflection
and completely specular transmission.

If you had semi-specular reflection, semi-diffuse transmission or complex
geometry raytracing is more likely to result in higher accuracy in less time
than radiosity.

Andy

···

On 8/13/09 1:58 PM, "Greg Ward" <[email protected]> wrote:

Can you send me your scene description, so I can have a look at it?
This is the worst possible timing for me, but you're going to get
nowhere unless you share your scene files. It's impossible to deduce
what's going wrong from an image.

-Greg

From: [email protected]
Date: August 13, 2009 1:42:40 PM PDT

Hmm, well no suggestions thus far has helped solve the problem I am
having. I think it would help if I explain what I am trying to do. I
am
attempting to validate radiosity calculations against a raytracer (in
this case Radiance). I am doing this with a simple example of a box
lit
only by direct sun and ambient bounces, so there is no sky
distribution.

I have attempted many different rendering options, such as -aa 0 and
many
other "high quality" level options as recommended in the Rendering
with
Radiance book. These do not get rid of the problem. As you can see
in my
gensky below, the sun shouldn't be approaching the zenith, as it has
been
revealed can cause problems.

I was reccommended to try using mkillum to turn the window into an
illum
surface. I have attempted this, but it doesn't appear to do
anything, so
I could be using it incorrectly? I am only using a single ambient
bounce
in my calculations because the shadow is still there even on higher
amounts, such as -ab 20. I decided -ab 1 would make it easier to track
down the problem as well as take less computation time.

Any more thoughts on what could be causing this? Could it be a problem
with gensky similar to the zenith problem maybe?

--John Schwartz

From: [email protected]
Date: July 27, 2009 3:41:40 PM PDT

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into
my room.

I am using the following gensky to attempt to only light the room
using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
0
4 0 0 0 0

sky_glow source sky
0
0
4 0 0 1 180

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg>
You'll note on this image, that there is a strange shadow on the >
ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the
"back" of
the box, with the light on the ceiling instead of the floor. There
is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpg
This > picture was rendered using -ab 0>
Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not
causing
the shadow, instead the highlight on the floor causes the shadow on
the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

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

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

Wow, reducing the -as to 0 seems to have relieved the problem. I had no
idea that they don't shoot directly up (I had guessed it might have been
something along those lines, but couldn't track it down).

The RwR book seems to suggest that you use a -as equal to 1/4 your -ad,
so I can't imagine that reducing the -as to 0 should be the correct
solution... Perhaps the model I am using simply exacerbates this issue?

Could you explain when it's reasonable to use -as 0 and a large -ad, as
opposed to the values recommended in the book? Does it depend on the size
of the highlight on the floor (smaller = more/less -as )?

Naturally like you suggested Andrew, this model is much faster to do with
radiosity. It's really just a test model, and naturally more complex
models would have to be used. However after I saw this, I naturally
couldn't proceed with image comparisons until I figured out what I was
doing wrong! As you've probably seen, I've sent out the scene, so if you
have any further insights, especially into what rpict options I should be
using, do tell.

--John Schwartz

==============Original message text===============

John,

I'd also like to see your scene, but while I wait I'll go out on a limb:
AFAIK in radiance, an ambient sample ray is never emitted normal to a
surface. I suspect your shadow results from the (slightly) decreased
probability of sampling the highlight from the area directly above the
highlight. This effect can be compounded by the -as setting (which never
samples the upper edge of a division, but can sample the lower edge of a
division).

My suggestion: try a high ad value coupled with no ambient super samples.
-ad 20000 -as 0

As far as your comparison between raytracing and radiosity, You pick a scene
that plays to all the strengths of radiosity. Radiosity with a dense mesh
produces a highly accurate result in relatively little time for scenes that
have very simple geometry and are limited to completely diffuse reflection
and completely specular transmission.

If you had semi-specular reflection, semi-diffuse transmission or complex
geometry raytracing is more likely to result in higher accuracy in less time
than radiosity.

Andy

···

On Thu, 13 Aug 2009 18:01:09 EDT Andrew McNeil wrote:

On 8/13/09 1:58 PM, "Greg Ward" <[email protected]> wrote:

Can you send me your scene description, so I can have a look at it?
This is the worst possible timing for me, but you're going to get
nowhere unless you share your scene files. It's impossible to deduce
what's going wrong from an image.

-Greg

From: [email protected]
Date: August 13, 2009 1:42:40 PM PDT

Hmm, well no suggestions thus far has helped solve the problem I am
having. I think it would help if I explain what I am trying to do. I
am
attempting to validate radiosity calculations against a raytracer (in
this case Radiance). I am doing this with a simple example of a box
lit
only by direct sun and ambient bounces, so there is no sky
distribution.

I have attempted many different rendering options, such as -aa 0 and
many
other "high quality" level options as recommended in the Rendering
with
Radiance book. These do not get rid of the problem. As you can see
in my
gensky below, the sun shouldn't be approaching the zenith, as it has
been
revealed can cause problems.

I was reccommended to try using mkillum to turn the window into an
illum
surface. I have attempted this, but it doesn't appear to do
anything, so
I could be using it incorrectly? I am only using a single ambient
bounce
in my calculations because the shadow is still there even on higher
amounts, such as -ab 20. I decided -ab 1 would make it easier to track
down the problem as well as take less computation time.

Any more thoughts on what could be causing this? Could it be a problem
with gensky similar to the zenith problem maybe?

--John Schwartz

From: [email protected]
Date: July 27, 2009 3:41:40 PM PDT

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into
my room.

I am using the following gensky to attempt to only light the room
using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
0
4 0 0 0 0

sky_glow source sky
0
0
4 0 0 1 180

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg>>>> You'll note on this image, that there is a strange shadow on the >
ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the
"back" of
the box, with the light on the ceiling instead of the floor. There
is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpg>>> This > picture was rendered using -ab 0>
Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not
causing
the shadow, instead the highlight on the floor causes the shadow on
the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

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

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

===========End of original message text===========

John,

I'm running your scene and am witnessing the same effect. Interestingly the
dark spot still exists, it is just much less pronounced.

I am both able and unable to understand why this works.

Years ago I remember someone mentioning the impossibility of ambient
sampling normal to a surface and it's lingered in my mind ever since. I've
always struggled with the ambient calculation's ability to sample the
horizon which technically contributes nothing to illuminance at a point
while it was unable to sample the zenith which contributes most to
illuminance.

I've thought about suggesting the range for ambient sampling switch from
[0,1) to (0,1] but couldn't grasp the ramifications of the possibility of
sampling the zenith from all of the zenith adjacent ambient divisions.

It seems to me that statistically it isn't possible for this to make a
difference so maybe there is a bug in the ambient super sampling, but it
also seems to me that statistically this must make a difference.

So I guess I'll just have to wait for Greg and others to weigh in...

Andy

···

On 8/13/09 4:05 PM, "[email protected]" <[email protected]> wrote:

Wow, reducing the -as to 0 seems to have relieved the problem. I had no
idea that they don't shoot directly up (I had guessed it might have been
something along those lines, but couldn't track it down).

The RwR book seems to suggest that you use a -as equal to 1/4 your -ad,
so I can't imagine that reducing the -as to 0 should be the correct
solution... Perhaps the model I am using simply exacerbates this issue?

Could you explain when it's reasonable to use -as 0 and a large -ad, as
opposed to the values recommended in the book? Does it depend on the size
of the highlight on the floor (smaller = more/less -as )?

Naturally like you suggested Andrew, this model is much faster to do with
radiosity. It's really just a test model, and naturally more complex
models would have to be used. However after I saw this, I naturally
couldn't proceed with image comparisons until I figured out what I was
doing wrong! As you've probably seen, I've sent out the scene, so if you
have any further insights, especially into what rpict options I should be
using, do tell.

--John Schwartz

==============Original message text===============
On Thu, 13 Aug 2009 18:01:09 EDT Andrew McNeil wrote:

John,

I'd also like to see your scene, but while I wait I'll go out on a limb:
AFAIK in radiance, an ambient sample ray is never emitted normal to a
surface. I suspect your shadow results from the (slightly) decreased
probability of sampling the highlight from the area directly above the
highlight. This effect can be compounded by the -as setting (which never
samples the upper edge of a division, but can sample the lower edge of a
division).

My suggestion: try a high ad value coupled with no ambient super samples.
-ad 20000 -as 0

As far as your comparison between raytracing and radiosity, You pick a scene
that plays to all the strengths of radiosity. Radiosity with a dense mesh
produces a highly accurate result in relatively little time for scenes that
have very simple geometry and are limited to completely diffuse reflection
and completely specular transmission.

If you had semi-specular reflection, semi-diffuse transmission or complex
geometry raytracing is more likely to result in higher accuracy in less time
than radiosity.

Andy

On 8/13/09 1:58 PM, "Greg Ward" <[email protected]> wrote:

Can you send me your scene description, so I can have a look at it?
This is the worst possible timing for me, but you're going to get
nowhere unless you share your scene files. It's impossible to deduce
what's going wrong from an image.

-Greg

From: [email protected]
Date: August 13, 2009 1:42:40 PM PDT

Hmm, well no suggestions thus far has helped solve the problem I am
having. I think it would help if I explain what I am trying to do. I
am
attempting to validate radiosity calculations against a raytracer (in
this case Radiance). I am doing this with a simple example of a box
lit
only by direct sun and ambient bounces, so there is no sky
distribution.

I have attempted many different rendering options, such as -aa 0 and
many
other "high quality" level options as recommended in the Rendering
with
Radiance book. These do not get rid of the problem. As you can see
in my
gensky below, the sun shouldn't be approaching the zenith, as it has
been
revealed can cause problems.

I was reccommended to try using mkillum to turn the window into an
illum
surface. I have attempted this, but it doesn't appear to do
anything, so
I could be using it incorrectly? I am only using a single ambient
bounce
in my calculations because the shadow is still there even on higher
amounts, such as -ab 20. I decided -ab 1 would make it easier to track
down the problem as well as take less computation time.

Any more thoughts on what could be causing this? Could it be a problem
with gensky similar to the zenith problem maybe?

--John Schwartz

From: [email protected]
Date: July 27, 2009 3:41:40 PM PDT

I am fairly stumped as to what is going on here. I have a box with a
square hole, 1/3 x 1/3 the width of the box, to allow sunlight into
my room.

I am using the following gensky to attempt to only light the room
using
sunlight.
!gensky 6 21 12:00EST -a 40.77 -o 73.967 -g 0.0 +s
skyfunc glow sky_glow
0
0
4 0 0 0 0

sky_glow source sky
0
0
4 0 0 1 180

This picture was rendered using -ab 1
http://i639.photobucket.com/albums/uu111/radiancebox/radiance.jpg>>>>
You'll note on this image, that there is a strange shadow on the >
ceiling.
I am unable to figure out why.

If I instead place a light in the room, also 1/3x 1/3 the size of the
box, I do not have this problem. This picture is taken from the
"back" of
the box, with the light on the ceiling instead of the floor. There
is no
gensky used on this picture.

http://i639.photobucket.com/albums/uu111/radiancebox/Light.jpg>>> This >
picture was rendered using -ab 0>
Changing the camera angle doesn't effect the shadow seen in the first
picture. I have determined that the shape of the window is not
causing
the shadow, instead the highlight on the floor causes the shadow on
the
ceiling.

If anyone can help clear this up for me, I would appreciate it.

--John

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

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Hi John,

I spent a little time looking at your model, and there are some irregularities that I'm not sure are intentional. Specifically, I rendered a view from the darker region of the ceiling looking down like so:

Hah -- looks like Andy arrived at the same conclusion, though a bit more speculatively. Well done!

There are methods for sampling a hemisphere without the singularity at the zenith, but they are a lot trickier to implement.

-Greg

···

From: Andrew McNeil <[email protected]>
Date: August 13, 2009 4:31:25 PM PDT

John,

I'm running your scene and am witnessing the same effect. Interestingly the
dark spot still exists, it is just much less pronounced.

I am both able and unable to understand why this works.

Years ago I remember someone mentioning the impossibility of ambient
sampling normal to a surface and it's lingered in my mind ever since. I've
always struggled with the ambient calculation's ability to sample the
horizon which technically contributes nothing to illuminance at a point
while it was unable to sample the zenith which contributes most to
illuminance.

I've thought about suggesting the range for ambient sampling switch from
[0,1) to (0,1] but couldn't grasp the ramifications of the possibility of
sampling the zenith from all of the zenith adjacent ambient divisions.

It seems to me that statistically it isn't possible for this to make a
difference so maybe there is a bug in the ambient super sampling, but it
also seems to me that statistically this must make a difference.

So I guess I'll just have to wait for Greg and others to weigh in...

Andy

Hi John,

I spent a little time looking at your model, and there are some irregularities that I'm not sure are intentional. Specifically, I rendered a view from the darker region of the ceiling looking down like so:

[...]

The light patch is the one seen at the bottom of your original view, but the dark patch below it (actually towards the camera in your first view) is peculiar. It appears to be an opening, where light goes but does not return. Was this what you meant to do? Are you radiosity calculations OK with this? Infinite rays may cause some oddities in the interpolation, which I think is at least part of what we are seeing in the 10-20% level drop in the dark patch on the ceiling.

The dark patch should be the window opening. The ground glow has been removed
from the sky description so you look into the ...

... cold dark void. [cue flash and rolling thunder]

Thomas :wink:

···

On Fri, Aug 14, 2009 at 12:44 AM, Greg Ward <[email protected]> wrote:

Hi John,

Even without this funny sampling behavior I think there could be a slightly darker patch on the ceiling due to the 1/3 x 1/3 square on the adjacent wall that has a 0% reflectance. That dark portion of the ceiling could just have a stronger coupling to the 0% reflectance surface than the other surfaces around. Do your radiosity renderings show any darker spots on the ceiling?

Cheers,
Zack

···

________________________________

  ZACK ROGERS, P.E., LEED AP, IESNA

INTEGRATED DESIGN ASSOCIATES, INC
437 Main Street
Longmont, CO 80501
tel: 303.848.8299, fax: 303.848.8290
www.ideasi.com

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Thomas Bleicher
Sent: Friday, August 14, 2009 2:58 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] Shadow above highlight?

On Fri, Aug 14, 2009 at 12:44 AM, Greg Ward <[email protected]> wrote:

Hi John,

I spent a little time looking at your model, and there are some irregularities that I'm not sure are intentional. Specifically, I rendered a view from the darker region of the ceiling looking down like so:

[...]

The light patch is the one seen at the bottom of your original view, but the dark patch below it (actually towards the camera in your first view) is peculiar. It appears to be an opening, where light goes but does not return. Was this what you meant to do? Are you radiosity calculations OK with this? Infinite rays may cause some oddities in the interpolation, which I think is at least part of what we are seeing in the 10-20% level drop in the dark patch on the ceiling.

The dark patch should be the window opening. The ground glow has been removed from the sky description so you look into the ...

... cold dark void. [cue flash and rolling thunder]

Thomas :wink:

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

I might agree with you, but I think if it was the window, then not only
the ceiling, but also the right and left walls would probably have dark
spots on them as well (maybe also the backwall?). It should be noted that
the dark spot is always directly above the highlight on the floor as the
time of day changes. I don't really understand what you mean by coupling,
but I don't believe that the shadow is related to the window, rather it
is related to the highlight on the floor. If I change the shape of the
aperture to an asymmetrical shape, such as a square with a triangle on
top, then the shadow on the ceiling seems to be a mirror image of the
highlight on the floor, rather than a projection of the window. Note that
the two would have the triangle shape on opposite sides of the ceiling
shadow. I'm not sure if that helps answer your question.

The radiosity program I am using does not create a shadow in that
location, (or on other walls either). I believe if anything, radiosity
might simply be darker/lighter in general.

--John

==============Original message text===============

···

On Mon, 17 Aug 2009 13:24:46 EDT "Zack Rogers" wrote:

Hi John,

Even without this funny sampling behavior I think there could be a
slightly darker patch on the ceiling due to the 1/3 x 1/3 square on the
adjacent wall that has a 0% reflectance. That dark portion of the
ceiling could just have a stronger coupling to the 0% reflectance surface
than the other surfaces around. Do your radiosity renderings show any
darker spots on the ceiling?

Cheers,
Zack

________________________________

  ZACK ROGERS, P.E., LEED AP, IESNA

INTEGRATED DESIGN ASSOCIATES, INC
437 Main Street
Longmont, CO 80501
tel: 303.848.8299, fax: 303.848.8290
www.ideasi.com

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Thomas
Bleicher
Sent: Friday, August 14, 2009 2:58 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] Shadow above highlight?

On Fri, Aug 14, 2009 at 12:44 AM, Greg Ward <[email protected]> wrote:

Hi John,

I spent a little time looking at your model, and there are some

irregularities that I'm not sure are intentional. Specifically, I
rendered a view from the darker region of the ceiling looking down like so:

[...]

The light patch is the one seen at the bottom of your original view,

but the dark patch below it (actually towards the camera in your first
view) is peculiar. It appears to be an opening, where light goes but
does not return. Was this what you meant to do? Are you radiosity
calculations OK with this? Infinite rays may cause some oddities in the
interpolation, which I think is at least part of what we are seeing in
the 10-20% level drop in the dark patch on the ceiling.

The dark patch should be the window opening. The ground glow has been
removed from the sky description so you look into the ...

... cold dark void. [cue flash and rolling thunder]

Thomas :wink:

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
===========End of original message text===========

I agree with John that the root cause of the shadow is the sampling behavior
of Radiance. With only one ambient bounce the black hole in the window, and
the walls in general shouldn't affect the luminance of the ceiling.

If there were more than one bounce, than the black hole would be a factor,
but it would probably be much less defined as all surfaces in the room see
the hole.

One way to test is to fill in the hole and create a polygon with glow
material to replace the sun patch on the floor.

Andy

···

On 8/17/09 10:52 AM, "[email protected]" <[email protected]> wrote:

I might agree with you, but I think if it was the window, then not only
the ceiling, but also the right and left walls would probably have dark
spots on them as well (maybe also the backwall?). It should be noted that
the dark spot is always directly above the highlight on the floor as the
time of day changes. I don't really understand what you mean by coupling,
but I don't believe that the shadow is related to the window, rather it
is related to the highlight on the floor. If I change the shape of the
aperture to an asymmetrical shape, such as a square with a triangle on
top, then the shadow on the ceiling seems to be a mirror image of the
highlight on the floor, rather than a projection of the window. Note that
the two would have the triangle shape on opposite sides of the ceiling
shadow. I'm not sure if that helps answer your question.

The radiosity program I am using does not create a shadow in that
location, (or on other walls either). I believe if anything, radiosity
might simply be darker/lighter in general.

--John

==============Original message text===============
On Mon, 17 Aug 2009 13:24:46 EDT "Zack Rogers" wrote:

Hi John,

Even without this funny sampling behavior I think there could be a
slightly darker patch on the ceiling due to the 1/3 x 1/3 square on the
adjacent wall that has a 0% reflectance. That dark portion of the
ceiling could just have a stronger coupling to the 0% reflectance surface
than the other surfaces around. Do your radiosity renderings show any
darker spots on the ceiling?

Cheers,
Zack

________________________________

  ZACK ROGERS, P.E., LEED AP, IESNA

INTEGRATED DESIGN ASSOCIATES, INC
437 Main Street
Longmont, CO 80501
tel: 303.848.8299, fax: 303.848.8290
www.ideasi.com

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Thomas
Bleicher
Sent: Friday, August 14, 2009 2:58 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] Shadow above highlight?

On Fri, Aug 14, 2009 at 12:44 AM, Greg Ward <[email protected]> wrote:

Hi John,

I spent a little time looking at your model, and there are some

irregularities that I'm not sure are intentional. Specifically, I
rendered a view from the darker region of the ceiling looking down like so:

[...]

The light patch is the one seen at the bottom of your original view,

but the dark patch below it (actually towards the camera in your first
view) is peculiar. It appears to be an opening, where light goes but
does not return. Was this what you meant to do? Are you radiosity
calculations OK with this? Infinite rays may cause some oddities in the
interpolation, which I think is at least part of what we are seeing in
the 10-20% level drop in the dark patch on the ceiling.

The dark patch should be the window opening. The ground glow has been
removed from the sky description so you look into the ...

... cold dark void. [cue flash and rolling thunder]

Thomas :wink:

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
===========End of original message text===========

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

____________________________________________________________
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systems are scanned for acceptability of content and viruses