Re: [Algorithms] Bicubic normals for a bicubic world

[Conor S. <cs...@tp...>]

    Actually, if you think about it - The normals are totally quadratic. And
if you do a derivitive in 2
directions (across S, and across T) you do get 2 quadratics. Not only that,
the cross product is
resiliant to transforms - So it remains the same. However, normalisation
still needs to occur.

    This is why I precalc my normals and reference them from a map in most
cases.

Conor Stokes


> Ok, maybe reducing it to 2D wasn't such a good idea.
>
> What we really want is a curve that descibes the surface normal of a
bicubic
> surface. This normal is the cross product of two tangents, one in u and
one
> in v. Each of these tangent surfaces is a partial derivative, so while
it's
> a quadratic in one parameter, it's a still cubic in the other.
>
> If you can fit that into a biquadratic surface, I'd like to see it, 'cause
I
> can sure use it! ;-)
>
> John Sensebe
> jse...@ho...
> Quantum mechanics is God's way of ensuring that we never really know
what's
> going on.
>
> Check out http://members.home.com/jsensebe to see prophecies for the
coming
> Millennium!
>
>
> ----- Original Message -----
> From: "Tom Forsyth" <to...@mu...>
> To: <gda...@li...>
> Sent: Thursday, August 10, 2000 9:55 AM
> Subject: RE: [Algorithms] Bicubic normals for a bicubic world
>
>
> > No - in the S shape, each component of the normal goes from value A to
> value
> > B and back to value A, which can be described by a quadratic.
> >
> > Tom Forsyth - Muckyfoot bloke.
> > Whizzing and pasting and pooting through the day.
> >
>
>
>
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