lighting per pixel or per face? - obj2mesh(new)

radiance-general
1

ok, thanks for the information! I think I'll try a more professional modelling tool.

I was thinking that maybe there was a way to interpolate normals and find each normal per pixel.. so I supposed that lighting would be smoother.

Thanks again,
Despina

···

----- Original Message ----- From: "Gregory J. Ward" <gregoryjward@gmail.com>
To: "Radiance general discussion" <radiance-general@radiance-online.org>
Sent: Friday, March 25, 2005 11:19 PM
Subject: Re: [Radiance-general] lighting per pixel or per face? - obj2mesh(new)

Hi Despina,

If your geometry actually contains these creases, which it does, how can you expect Radiance NOT to render them? The .OBJ file you sent me has numerous problems. The creases are caused by incorrect surface normals at the patch boundaries. If you take these out by running obj2rad -f, then you see the polygonal faces and get a lot of warnings about non-planar polygons. I didn't check to determine if your polygons really are non-planar or if it's simply an issue with too few significant digits in your vertex coordinates.

I would recommend a different modeling system.
-Greg

From: "Despina Michael" <despina_m81@hotmail.com>
Date: March 25, 2005 12:46:41 PM PST

hello all again,

well I finally managed to run obj2mesh (after installing last version of Radiance)
the result is somehow different but still not enough good.
http://www2.cs.ucy.ac.cy/~cs99dm1/res1mesh.jpg (new result)
http://www2.cs.ucy.ac.cy/~cs99dm1/resultRadiance.jpg (old result)

Is there anyway to make the lighting even smoother?

Thanks!
Despina

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2

ok, thanks for the information! I think I'll try a more professional
modelling tool.

I was thinking that maybe there was a way to interpolate normals and find
each normal per pixel.. so I supposed that lighting would be smoother.

Hi!

So-called smooth rendering is a topic again and again. In fact, many
modeling apps provide some kind of smooth rendering, but still there are few
ways to get such smooth models from one polygon-based app to another.

The only way I found to work reasonable well is using "fixed-angle"
smoothing together with 3ds or obj formats. This will make most modelers
forget all normals (also the wrong surface normals :wink: and generate the
interpolated normals for export if the angle between surfaces is over a
value you have to specify. I am using this with success in formZ. You may
habe to "mesh" the objects before you export them, as sometimes, the
calculation of the interpolated normals works only on triangles, at least
flat polygons. I usually triangulate everything, than export as obj with
"smoothed" interpolated normals support from formZ.

The other problem that may arise is that your model's geometry is not clean.
In radiance, you need "watertight" models, that means you have to work
accurately. If there is a gap between surfaces, even if small and almost
invisible, this produces errors. E.g. the interpolation described won't work
when exporting, and, worse, you will have light leakage, getting light where
it should not be in the model. So the model quality (as in all simulations)
is really important.

You might find a lot of information about clean meshes if you google for
mesh generators, as they are used in industry for building "real" physical
models, e.g. by litografie, 3d-printing, cnc... These processes need clean,
meshed models, and there is a huge amount of tools available to produce and
process mesh geometry.

The key problem is that all importers for radiance support more or less
primitive types. There is no support for nurbs, and many formats even reduce
everything to polygons. Radiance itself doesn't only support "flat"
surfaces, however, this won't help if you can't import e.g. a ball as a
ball, but only as a mesh following its surface, or write the radiance scene
with your favorite text editor :wink: The lack of support for these more
complicated objects is related to radiance's application, which is
simulation of buildings - and most of our built environment is made of
polygonal surfaces :wink:

CU Lars.

3

Hello Lars,
thank you very much for your reply and for your tips!
after your explanation, I guess I got a better idea what is going on with normals

Thanks,
Despina

···

----- Original Message ----- From: "Lars Grobe" <grobe@gmx.net>
To: "Radiance general discussion" <radiance-general@radiance-online.org>
Sent: Sunday, March 27, 2005 10:30 PM

Hi!

So-called smooth rendering is a topic again and again. In fact, many
modeling apps provide some kind of smooth rendering, but still there are few
ways to get such smooth models from one polygon-based app to another.

The only way I found to work reasonable well is using "fixed-angle"
smoothing together with 3ds or obj formats. This will make most modelers
forget all normals (also the wrong surface normals :wink: and generate the
interpolated normals for export if the angle between surfaces is over a
value you have to specify. I am using this with success in formZ. You may
habe to "mesh" the objects before you export them, as sometimes, the
calculation of the interpolated normals works only on triangles, at least
flat polygons. I usually triangulate everything, than export as obj with
"smoothed" interpolated normals support from formZ.

The other problem that may arise is that your model's geometry is not clean.
In radiance, you need "watertight" models, that means you have to work
accurately. If there is a gap between surfaces, even if small and almost
invisible, this produces errors. E.g. the interpolation described won't work
when exporting, and, worse, you will have light leakage, getting light where
it should not be in the model. So the model quality (as in all simulations)
is really important.

You might find a lot of information about clean meshes if you google for
mesh generators, as they are used in industry for building "real" physical
models, e.g. by litografie, 3d-printing, cnc... These processes need clean,
meshed models, and there is a huge amount of tools available to produce and
process mesh geometry.

The key problem is that all importers for radiance support more or less
primitive types. There is no support for nurbs, and many formats even reduce
everything to polygons. Radiance itself doesn't only support "flat"
surfaces, however, this won't help if you can't import e.g. a ball as a
ball, but only as a mesh following its surface, or write the radiance scene
with your favorite text editor :wink: The lack of support for these more
complicated objects is related to radiance's application, which is
simulation of buildings - and most of our built environment is made of
polygonal surfaces :wink:

CU Lars.

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Radiance-general mailing list
Radiance-general@radiance-online.org
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