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29 Jul 2024 18:30:21 EDT (-0400)
  strange shading (Message 1 to 5 of 5)  
From: sokermaniac11
Subject: strange shading
Date: 18 Jul 2005 18:15:01
Message: <web.42dc2937c2ea591bec84c21d0@news.povray.org>
Im trying to use a mesh of smooth_triangles to generate a molecular
structure. The structure generates fine, but the shading looks like its
coming from a completely different light source than the one i defined. I
defined an area light directly out from the origin (about 500 units on the
z axis), and have my camera looking at the origin and located along the z
axis just like the light, just not as far out. I assumed this would
generate shading based on the shape of the object. However, the left and
right edges are extremely bright and the center so dark the shape is almost
completely lost... I increased the ambience of my textures which helped
some, but the shape of the object is still lost at the center. I tried
adding a second light source but it just made the current result more
drastic... Am I just missing something?


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From: Mike Williams
Subject: Re: strange shading
Date: 18 Jul 2005 23:20:29
Message: <CQWj7AA5DH3CFwbX@econym.demon.co.uk>
Wasn't it sokermaniac11 who wrote:
>Im trying to use a mesh of smooth_triangles to generate a molecular
>structure. The structure generates fine, but the shading looks like its
>coming from a completely different light source than the one i defined. I
>defined an area light directly out from the origin (about 500 units on the
>z axis), and have my camera looking at the origin and located along the z
>axis just like the light, just not as far out. I assumed this would
>generate shading based on the shape of the object. However, the left and
>right edges are extremely bright and the center so dark the shape is almost
>completely lost... I increased the ambience of my textures which helped
>some, but the shape of the object is still lost at the center. I tried
>adding a second light source but it just made the current result more
>drastic... Am I just missing something?

Is it possible that you've calculated your normals incorrectly. For
example, if they're all pointing in the opposite direction from what
they should be, then the surface would look smooth and continuous but
the shading would be inside out.

-- 
Mike Williams
Gentleman of Leisure


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From: Warp
Subject: Re: strange shading
Date: 19 Jul 2005 01:52:41
Message: <42dc9529@news.povray.org>
A simple example scene would help answering your question a lot...

-- 

                                                          - Warp


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From: sokermaniac11
Subject: Re: strange shading
Date: 19 Jul 2005 13:15:01
Message: <web.42dd34d0fa1fe4541068d2140@news.povray.org>
Quote:
> Is it possible that you've calculated your normals incorrectly. For
> example, if they're all pointing in the opposite direction from what
> they should be, then the surface would look smooth and continuous but
> the shading would be inside out.

Its possible that ive calculated the normals incorrectly. Im actually
starting from a vrml file generated by a modeling program which contains
the normals. Then I use the vectors from the vrml file and write my pov.
And I know the file works correctly in the modeling program... Is there a
conversion factor or difference between vrml normals and pov normals that
im not aware of?

>A simple example scene would help answering your question a lot...

How would I go about posting an example scene? Im not able to post
attachments on the newsgroup so what would be the easiest way?

Thank you!

Jammin


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From: sokermaniac11
Subject: Re: strange shading
Date: 19 Jul 2005 16:25:00
Message: <web.42dd6136fa1fe4541068d2140@news.povray.org>
Ok I figured it out. The problem WAS the normals. The modeling program i was
using is a right-handed universe, while POV is a left-handed. So i just
used a matrix to switch POV to a right handed and things suddenly worked.
Thank you for your help!!

Jammin


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