[CST-2] Advanced Graphics

[Chris Applegate]

The big perpendicular vector from the surface will be something like
(-x, y ,z), so that does depend on x.

But when you normalise it to unit size by dividing by root(x^2 + y^2 +
z^2) = root(2x^2) then the x term cancels to become 1/root(2)...thus
constant...and the others become y/x*root(2) and z/x*root(2).

Cheerio,

Chris
do something lastminute.work

Chris Applegate
Room X6, Corpus Christi College, Cambridge, CB2 1RH
chris@qwghlm.co.uk / www.qwghlm.co.uk / [Redacted by SRCF sysadmins on request]
ICQ 41706821          PGP key available on request

> -----Original Message-----
> From: cst-2-admin@srcf.ucam.org [mailto:cst-2-admin@srcf.ucam.org]On
> Behalf Of Jamie Shotton
> Sent: 1 June 2002 16:07
> To: cst-2@srcf.ucam.org
> Subject: RE: [CST-2] Advanced Graphics
>
>
>
>
> Are you sure:
> Imagine a normal vector close the origin and the direction it is
> pointing.  Then move out to say 100 * the original x.  If x doesn't
> change, but the normal does depend on y and z then the normal vector
> will point in a much more outwards direction than before, and that is
> clearly wrong as it needs to point the same way regardless of x.
>
> J
>
>
> >
> > Good point, but there is no difference between the
> > x-component of the normal at x=1 and x=2 (which is what I was
> > trying to get).
> >
> > Which side of x=0 the point lies will change the sign of the
> > component, but not its magnitude.
> >
> > Cheerio,
> >
> > Chris
> > do something lastminute.work
> >
> > Chris Applegate
> > Room X6, Corpus Christi College, Cambridge, CB2 1RH
> > chris@qwghlm.co.uk / www.qwghlm.co.uk / [Redacted by SRCF sysadmins on request]
> > ICQ 41706821          PGP key available on request
> >
> >
> >
> > > -----Original Message-----
> > > From: cst-2-admin@srcf.ucam.org
[mailto:cst-2-admin@srcf.ucam.org]On
> > Behalf Of Chris North
> > Sent: 1 June 2002 15:58
> > To: cst-2@srcf.ucam.org
> > Subject: RE: [CST-2] Advanced Graphics
> >
> >
> > No, the normal DOES depend on x.  For instance, what do you think
> > happens if the intersection point changes from x=1 to
> x=-1??  It will
> > point in opposite
> > directions with respect to x is what.  Therefore there has to
> > be a dependence.
> >
> > HTH
> >
> > --
> > Chris North
> > This address will soon be terminated, please
> > use norfus@cantab.net instead :)
> >
> >
> > _______________________________________________
> > CST-2 mailing list
> > CST-2@srcf.ucam.org http://www.srcf.ucam.org/mailman/listinfo/cst-2
>
>
>
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