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From: Jörg 'Yadgar' Bleimann
Subject: Excluding objects from radiosity?
Date: 5 May 2005 18:34:19
Message: <427a9f6b@news.povray.org>
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High!
For an flyby sequence over my - still very crude - Afghan landscape I
added a sky with cheap bozo clouds on a hollow sphere 6000 metres above
ground... and when I started rendering the animation, I noticed that a
part of the clouds, which should, even when seen from the unlit side, be
light grey, is rendered almost black!
As this blackness doesn't show up when leaving out the terrain, I
concluded that this is caused by radiosity, which darkens the clouds
from the shadowed terrain below them (the darker mountains on the right
half the horizon in the first image).
So, I would like to know if there is a method to exclude an object from
being affected by radiosity...
See you in Khyberspace!
Yadgar
Now playing: Feuerland (Michael Rother)
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Attachments:
Download '2005-05-06_sar-e_helmand_overflight_frame.jpg' (56 KB)
Download '2005-05-06_sar-e_helmand_overflight_frame_sky_only.jpg' (22 KB)
Preview of image '2005-05-06_sar-e_helmand_overflight_frame.jpg'
Preview of image '2005-05-06_sar-e_helmand_overflight_frame_sky_only.jpg'
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Eh, unless you use negative light somewhere, radiosity won't add darkness to
objects...
Does this problem really *only* occur when switching radiosity on/off? You
don't switch positions for the lights or such, perhaps causing shadows onto
the clouds? Additionally, I'm not sure how radiosity works in conjunction
with double_illuminate.
--
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>
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=?ISO-8859-1?Q?J=F6rg_=27Yadgar=27_Bleimann?= <yaz### [at] gmx de> wrote:
> High!
>
> For an flyby sequence over my - still very crude - Afghan landscape I
> added a sky with cheap bozo clouds on a hollow sphere 6000 metres above
> ground... and when I started rendering the animation, I noticed that a
> part of the clouds, which should, even when seen from the unlit side, be
> light grey, is rendered almost black!
>
> As this blackness doesn't show up when leaving out the terrain, I
> concluded that this is caused by radiosity, which darkens the clouds
> from the shadowed terrain below them (the darker mountains on the right
> half the horizon in the first image).
>
> So, I would like to know if there is a method to exclude an object from
> being affected by radiosity...
>
> See you in Khyberspace!
>
> Yadgar
>
> Now playing: Feuerland (Michael Rother)
I don't know if you can exclude an object from exhibiting radiosity, but I'm
guessing that your sky sphere is brightly coloured in both the top part
(northern hemisphere) & the bottom part (southern hemisphere). In which
case, when you remove the ground, the bottom of your clouds are being lit
from below by the bottom part. When you put the ground in, you are
blocking the (unnatural) light from the sky below, leaving the clouds as
dark as they should be.
If you *want* the clouds to be lit from below, you could try using a
shadowless light_source some way below the ground, maybe putting it in a
light group with only the cloud sphere to prevent any other objects from
being underlit.
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From: Jörg 'Yadgar' Bleimann
Subject: Re: Excluding objects from radiosity? [JPG 800 x 600, 54343 bytes]
Date: 6 May 2005 06:36:45
Message: <427b48bd@news.povray.org>
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High!
Tim Nikias wrote:
> Eh, unless you use negative light somewhere, radiosity won't add darkness to
> objects...
No, there is no negative light in the scene, just one point_light
several million units away (note that the terrain is a mesh2 following
the curvature of Earth's surface!)
> Does this problem really *only* occur when switching radiosity on/off? You
> don't switch positions for the lights or such, perhaps causing shadows onto
> the clouds? Additionally, I'm not sure how radiosity works in conjunction
> with double_illuminate.
double_illuminate seems to work fine with radiosity (see attached
image), but I had to lower the gray value of the clouds' darkest part
(from 0.9 to 0.75), also the ambient from 0.15 to 0.05 to keep at least
a hint of structure with clouds - and still they appear too uniformly
bright.
And another problem occured: the parts of the terrain shadowed by the
clouds (right half of the horizon) are way too bright! They instead
should appear at least as dark as the shadowed parts in the foreground,
if not somewhat darker...
See you in Khyberspace!
Yadgar
Now playing: 12 o'Clock (Vangelis)
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Attachments:
Download '2005-05-06_sar-e_helmand_flyover_frame_take_2_(yadgar).jpg' (54 KB)
Preview of image '2005-05-06_sar-e_helmand_flyover_frame_take_2_(yadgar).jpg'
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From: Jörg 'Yadgar' Bleimann
Subject: Re: Excluding objects from radiosity? [JPG 800 x 600, 54343 bytes]
Date: 6 May 2005 19:42:19
Message: <427c00db$1@news.povray.org>
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High!
Perhaps I should add the radiosity settings for the latest scene... here
it is:
radiosity
{
pretrace_start 0.08
pretrace_end 0.01
count 50
nearest_count 4
error_bound 0.4
recursion_limit 1
low_error_factor 0.9
gray_threshold 0.75
minimum_reuse 0.015
brightness 1
adc_bailout 0.01/2
}
See you in Khyberspace!
Yadgar
Now playing: Come Together (The Beatles)
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From: Tim Nikias
Subject: Re: Excluding objects from radiosity? [JPG 800 x 600, 54343 bytes]
Date: 7 May 2005 05:00:05
Message: <427c8395$1@news.povray.org>
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> And another problem occured: the parts of the terrain shadowed by the
> clouds (right half of the horizon) are way too bright! They instead
> should appear at least as dark as the shadowed parts in the foreground,
> if not somewhat darker...
I don't see what you'e talking about. Underneath the clouds the terrain is
pretty dark. Maybe you misjudge the angle of the light and where the clouds'
shadows would fall?
As for why the clouds are that dark, I'm clueless. What you could try though
is to render the image in two passes: the first one saves the radiosity
using save_file and remove the clouds, the second pass will load the
radiosity and make use of the clouds. This might be a little tedious for the
animation though... Perhaps you should give scattering media a go?
--
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>
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From: Jörg 'Yadgar' Bleimann
Subject: Re: Excluding objects from radiosity? [JPG 800 x 600, 54343 bytes]
Date: 7 May 2005 06:44:23
Message: <427c9c07@news.povray.org>
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High!
Tim Nikias wrote:
> I don't see what you'e talking about. Underneath the clouds the terrain is
> pretty dark. Maybe you misjudge the angle of the light and where the clouds'
> shadows would fall?
No, I mean the third picture I posted in this thread... after I fixed
the darkness of the clouds, the terrain lying underneath turned too
bright... I posted it again for better understanding.
See you in Khyberspace!
Yadgar
Now playing: Battlefield from "Tarkus" (Emerson, Lake & Palmer)
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Attachments:
Download '2005-05-06_sar-e_helmand_flyover_frame_take_2_(yadgar).jpg' (54 KB)
Preview of image '2005-05-06_sar-e_helmand_flyover_frame_take_2_(yadgar).jpg'
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From: Tim Nikias
Subject: Re: Excluding objects from radiosity? [JPG 800 x 600, 54343 bytes]
Date: 7 May 2005 07:12:05
Message: <427ca285$1@news.povray.org>
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> No, I mean the third picture I posted in this thread... after I fixed
> the darkness of the clouds, the terrain lying underneath turned too
> bright... I posted it again for better understanding.
Well that's because you have some ambient on the clouds, using radiosity
they now emit light. Instead of adding ambient, try putting the clouds in a
lightgroup with a shadowless lightsource which will then only affect the
clouds, nothing else.
--
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>
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