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From: Hartmut Wagener
Subject: Problem with smooth triangles and smoothness (as in p.advanced_users)
Date: 7 Oct 2004 08:23:27
Message: <4165353f@news.povray.org>
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Hi,
here are the two example-pictures ...
What causes povray to render some parts unsmooth although the
norm-vectors seem to be calculated right?
Hartmut Wagener
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Attachments:
Download 'test2.jpg' (113 KB)
Download 'test.jpg' (18 KB)
Preview of image 'test2.jpg'
Preview of image 'test.jpg'
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From: Slime
Subject: Re: Problem with smooth triangles and smoothness (as in p.advanced_users)
Date: 7 Oct 2004 09:19:42
Message: <4165426e@news.povray.org>
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> What causes povray to render some parts unsmooth although the
> norm-vectors seem to be calculated right?
That particular triangle mesh has some extremely thin triangles inbetween
the larger ones. This is most visible near the lower left of the wireframe
image, right below where the banding begins in the other image.
This is causing a large part of the interpolation of normals to be done in a
very tiny space, so the normals of the adjacent larger triangles which make
up 99% of the surface in the problem areas do not match up.
- Slime
[ http://www.slimeland.com/ ]
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From: GrimDude
Subject: Re: Problem with smooth triangles and smoothness (as in p.advanced_users)
Date: 7 Oct 2004 15:05:27
Message: <41659377$1@news.povray.org>
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I believe you can correct issues like this with a good texture, but if that
doesn't fix the problem increasing the polygon count with a higher
isoline/surftab count usually will.
- Grim
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From: Hartmut Wagener
Subject: Re: Problem with smooth triangles and smoothness (as in p.advanced_users)
Date: 7 Oct 2004 15:50:05
Message: <41659ded$1@news.povray.org>
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Slime wrote:
>>What causes povray to render some parts unsmooth although the
>>norm-vectors seem to be calculated right?
>
>
>
> That particular triangle mesh has some extremely thin triangles inbetween
> the larger ones. This is most visible near the lower left of the wireframe
> image, right below where the banding begins in the other image.
>
> This is causing a large part of the interpolation of normals to be done in a
> very tiny space, so the normals of the adjacent larger triangles which make
> up 99% of the surface in the problem areas do not match up.
>
> - Slime
> [ http://www.slimeland.com/ ]
>
>
Whow, thats good. I have not seen this in the image i have posted but in
a later zoomed picture. I have posted in p.advanced_users that i want to
post the new picture tommorow.
The CAD-program makes these small triangles and the norm-vectors are
calculated bad ... And i was looking for the error in my java-program
for days ...
As mentioned in p.advusers i will try a newer version of the cad-program
(caddy ++) to see if there is something new ...
Hartmut
Post a reply to this message
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From: Hartmut Wagener
Subject: Re: Problem with smooth triangles and smoothness (as in p.advanced_users) (43kbbu)
Date: 8 Oct 2004 02:42:57
Message: <416636f1@news.povray.org>
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Hartmut Wagener wrote:
> Hi,
>
> here are the two example-pictures ...
>
> What causes povray to render some parts unsmooth although the
> norm-vectors seem to be calculated right?
>
> Hartmut Wagener
>
> ------------------------------------------------------------------------
>
>
> ------------------------------------------------------------------------
>
Here is a zoomed picture of the problematic triangles. I don't know how
to handle this. I have to look if the small triangles are parallel to
surrounding triangles and perhaps rewrite the code to run with planes
with more than three points.
Hartmut
Post a reply to this message
Attachments:
Download 'test3.jpg' (43 KB)
Preview of image 'test3.jpg'
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From: Slime
Subject: Re: Problem with smooth triangles and smoothness (as in p.advanced_users)
Date: 8 Oct 2004 10:21:21
Message: <4166a261$1@news.povray.org>
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> The CAD-program makes these small triangles and the norm-vectors are
> calculated bad ... And i was looking for the error in my java-program
> for days ...
I'm not sure exactly how CAD programs work, but don't they actually know the
shape they're working with, almost like POV-Ray primitives? If so, I would
expect that they could base the normal vectors off of the actual normals of
the shapes rather than off of the orientations of the nearby triangles. This
would avoid the problem even with the thin triangles there.
- Slime
[ http://www.slimeland.com/ ]
Post a reply to this message
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From: Hartmut Wagener
Subject: Re: Problem with smooth triangles and smoothness (as in p.advanced_users)
Date: 10 Oct 2004 15:06:35
Message: <4169883b@news.povray.org>
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Slime wrote:
>>The CAD-program makes these small triangles and the norm-vectors are
>>calculated bad ... And i was looking for the error in my java-program
>>for days ...
>
>
> I'm not sure exactly how CAD programs work, but don't they actually know the
> shape they're working with, almost like POV-Ray primitives? If so, I would
> expect that they could base the normal vectors off of the actual normals of
> the shapes rather than off of the orientations of the nearby triangles. This
> would avoid the problem even with the thin triangles there.
>
> - Slime
> [ http://www.slimeland.com/ ]
>
>
The used CAD-Program uses the SAT-Format of the ACIS-Kernel for
modelling. It is a volume-based Kernel working a little like Povray CSG
does. So the bad export is astonishing for me. Perhaps the problem lies
in the STL-Data with too much numbers after the point, i will check that
out. But i don't have the CAD-program working now, i need to borrow the
dongle to use the newest version. There are parameters that affect the
output of triangles.
Hartmut
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