[Radiance-general] lighting per pixel or per face? - obj2mesh(new)

[Despina Michael]

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 at gmx.net>
To: "Radiance general discussion" <radiance-general at 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 ;-) 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 ;-) 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 ;-)
>
> CU Lars.
>
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