Re: AW: Reflections..

["Tim Leydecker" <BauerOink(at)gmx.de>]

Hi there,

XSI has a default 60° interpolation angle set in the geometry aproximation
discontinuity tab, you should consider setting this value to either 30° or
35°, the first on resembles the default Maya value, the 35° one the default
Max value, don´t know about lightwave.

Basically, setting it anything just below 45° degrees should instantly give
you a better result - as reflections/smoothing isn´t bent around angles too large.

The above values should also give you a rough clue about how many
polygonsteps you´d need for a clean, soft bevel. By default, an XSI one
would probably look right with 2steps, Max would need 3steps and
Maya at_least 3steps to produce a smoothed result.

Since I transfer alot between XSI and Maya - I tend to set the angles for
my object to 30°, mostly several times as I haven´t found the global switch
for this.

Keep in mind while you loose those errors in reflections, you may run into
facetting due to now lower anglevales covered through surfacenormalinterpolation.

Cheers

tim



----- Original Message ----- 
From: "Xsiberger" <xsiberger(at)web.de>
To: <XSI(at)Softimage.COM>
Sent: Friday, June 02, 2006 8:31 PM
Subject: AW: AW: Reflections..


> sorry for the following questioning and repeating. i just wanted to make
> sure that I understand this correctly, because I am thinking of writing a
> small tutorial for this. that hole thing was bugging me for weeks. i figured
> out that adding geometry was solving the issue...but it is such a relief to
> finally understand what is going on. thank you André and everybody else who
> contributed to this!
>
> creating hard edges is breaking up the normals and reorienting them
> perpendicular to the corresponding polygon.
>
> through adding more geometry you get a better (more accurate) approximation
> between normals.
>
> the geometry approximation's discontinuity angle parameter is pretty much
> the same as creating hard edges except that you can control the angle how
> the normals are reoriented.
>
> creating more geometry over creating hard edges has the advantage of
> smoother highlights, what I can tell from a quick test or is there any other
> reason that someone should prefer adding more geometry rather than creating
> hard edges.
>
> I guess there is no way to manually modify (rotating) individual vertex
> normals in xsi?
>
> Is this an issue every 3d application/render engine has to deal with? I
> would expect (just curious).
>
> Rene
>
> -----Ursprüngliche Nachricht-----
> Von: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] Im Auftrag von
> Scott C. Lange
> Gesendet: Freitag, 2. Juni 2006 18:40
> An: XSI(at)Softimage.COM
> Betreff: RE: AW: Reflections..
>
> I just was dealing with the same exact issue. I had un-archived an old scene
> with a lot of reflection which I did not notice having this problem before.
> Please note that it is unsure whether these issues existed before. It was
> full up and rendered in 3.0 with out any noticeable issues in the
> reflection. Now I am modifying (a lot of it) that same scene and I have had
> to add hard edges and more local subdivisions to force the normals in the
> right direction. Just for your confirmation.
> -Scott
>
> -----Original Message-----
> From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of
> André Adam
> Sent: Friday, June 02, 2006 12:06 PM
> To: XSI(at)Softimage.COM
> Subject: Re: AW: Reflections..
>
> If you mean the reflection issue, that's rather quickly explained, to
> calculate reflection (as well as highlights and shading, btw) the
> surface's normals are evaluated to determine the surface's direction,
> which of course is needed to find out what's reflecting on this surface
> from the current point of view.
> Now, since we're dealing with triangles that are only an approximation
> of a real surface, the limited information of the vertex normals gets
> interpolated across the polygons. The distortions are caused by a too
> broad approximation of the modelled topology relative to what it is
> meant be.
> In Martin's example I guess the hole in the middle of the geometry is
> causing the problems where the unified vertex normals around the hole
> get bent towards the hole's center, therefore distorting the
> interpolated normals on the main surface.
> The quickest workaround is to create hard edges to break up the normals
> so that all normals contributing to the main-surface's normals point in
> the very same direction.
> A better fix would be to create more geometry at the right places to get
> a better triangle approximation of the real-life surface he is trying to
> simulate.
>
> Hope that helps and makes sense! Cheers!
>
>    -André
>
> Xsiberger wrote:
>
> > I also would appreciate any link/book which describes the theory behind
> this
> > phenomenon. is it called surface discontinuity? google didn't deliver
> > something usefull to this subject.
> >
> >
> >
> > -----Ursprüngliche Nachricht-----
> > Von: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] Im Auftrag
> von
> > Martin Belleau
> > Gesendet: Freitag, 2. Juni 2006 16:27
> > An: XSI(at)Softimage.COM
> > Betreff: RE: Reflections..
> >
> > Just like few people understand the concept of scene optimization. What's
> > clean and what isn't.
> >
> > Do you have a link so I can read up on this (normals)?
> >
> > -----Original Message-----
> > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of
> > kim aldis
> > Sent: Saturday, June 03, 2006 1:06 AM
> > To: XSI(at)Softimage.COM
> > Subject: RE: Reflections..
> >
> > It's to do with the way normals are calculated on points by averaging plane
> > normals of contributing faces.  If you have a think about how this works it
> > starts to make sense.
> >
> > An understanding of how shading works and how normals are built is
> > fundamental to good poly modeling and it always surprises me how few people
> > understand it.
> >
> > Chris, you still have your beveled cube thing kicking around?
> >
> >
> > -----Original Message-----
> > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of
> > Martin Belleau
> > Sent: 02 June 2006 14:37
> > To: XSI(at)Softimage.COM
> > Subject: RE: Reflections..
> >
> > Oki it works much better... But what happens if I don't want to use hard
> > edge, and use a Bevel...
> >
> >
> >
> >
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