Re: .mtl question

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Simon Mills (simon++at++wgs.estec.esa.nl)
Tue, 13 Jul 1999 09:04:38 +0200

Angus Dorbie wrote:
>
> Where did you get these terms from? The extension suggests a file format
> and that in turn suggests that this has little to do with Performer but
> rather the file format in question.

These terms are from the Wavefront OBJ object file format. An .obj
geometry file can refer to a .mtl material file with these keywords. See
the performer .obj file loader
/usr/share/Performer/src/lib/libpfdb/libpfobj/pfobj.c.

> Presumably they are from some lighting equation in the absence of that
> equation I'll guess.

They are material properties as defined by Wavefront.

> "d.pritchard++at++emedia.ca" wrote:
> >
> > Hi,
> >
> > I have a quick .mtl question. What does Ns, d, illum, Kd, Ks, Ka mean?
> > How do you make a listed material (non-.rgb and .rgb's) transparent?
> >
> > newmtl default
> > > Ns 32
> Shininess exponent
In the range 0-1000 (according to the manual) as opposed to 0-128 for
Performer.

> > > d 1
> ??
"Dissolve" = transparency or alpha in range 0.0-1.0.

> > > illum 2
> ?? some global modifier, or maybe a list of illuminating lights???
Illumination model 0-10. Not relevant for Performer since this indicates
increasingly sophisticated ray-tracing models. The only relevant ones
might be
0 = color on & ambient off i.e no lighting
1 = color on & ambient on i.e. only ambient lighting
2 = highlight on i.e. usual lighting with ambient/diffuse/specular

For example, I modified the standard OBJ loader to use this to
enable/disable lighting.

> > > Kd 0.4 0.4 0.4
> diffuse rgb
Correct.

> > > Ks 0.7 0.7 0.7
> specular rgb
Correct.

> > > Ka 0.3 0.3 0.3
>
> ambient rgb
Correct.

>
> Cheers,ANgus.
>
> --
> For years now, whenever NT has been proven to have some debilitating
> weakness we've heard from MS advocates that NT would catch up, there was
> just an incredible faith in this OS and Microsoft's ability to somehow
> get there. With the recent results of the Linux vs NT serving benchmark
> that same attitude can be seen in the Linux community. The Linux folks
> aren't too worried, "Sure the single threaded IP stack was slow but
> it'll be fixed in the next release.", it's eerily familiar but I have
> confidence in the Linux community's ability to remedy problems and I
> don't groan in pain as I used to when Microsoft made similar claims.
>
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-- 
Regards, Simon
________________________________________________________________________


Simon C. Mills
Modelling & Simulation Section (TOS-EMM)         Tel: +31 (0)71 565 3725
European Space Agency (ESA/ESTEC)                Fax: +31 (0)71 565 5419
Postbus 299, 2200AG Noordwijk             e-mail: simon++at++wgs.estec.esa.nl
The Netherlands                        http://www.estec.esa.nl/wmwww/EMM
________________________________________________________________________

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