Ok now I see. So it is not really tracing the ray but calculating the angles
and intersection points? I gather that this method is fast but also make the
math for radiosity hard. It also explains why media effects slow rendering
down tremendously.

As for why, To make a paper cup which is rather thin but not flat I would
have to model both the inside and out to create the thickness. That is a lot
of surfaces. And the edges still need to be beveled some how to create the
real highlight on the top rim. If the triangles could be rendered as though
they have a thickness then only the shape of the cup would need to be
rendered. The edges would naturally round over to the inside of the cup. It
would be more like the triangle only describe the center planes of the
object. It would be like using the triangle as a blob component where common
edges of each triangle would not be combined.

One of the hardest things I have tried to model is the smooth edges of
objects. Even a piece of paper bounces light off the very edges to show a
small but visible highlight. Basically I am looking for a short cut to
modeling true rounded edges. The real world does not have true sharp edges.
Now I know some are small enough to never be seen but our brains can and do
pick up these little missing parts. It is why indirect illumination is in
such use now. Trying for the most real looking images.

Take this as an artist trying to create the perfect image. Not as a
programmer and mathematician deriving algorithms.

Again thanks for that very good explanation.

"Warp" <war### [at] tagpovrayorg> wrote in message
news:3f4b422f@news.povray.org...
> "Micheal \(Mike\) Williams" <mic### [at] quixnetnet> wrote:
> > I have been toying with an idea. All objects in real life have a
thickness
> > to them. The metal of a car is thick enough that we can see it rounded
at
> > the edges. The idea is to treat triangles as though they have a
thickness.
>
>   Why? What would be the advantage of this?
>
> > The ray is incremented at a constant value. The triangle strike
> > point might just lay between he ray steps.
>
>   No, in raytracing rays are not incremented by steps (that would be
> awfully slow anyways).
>   The intersection of a ray with a surface is calculated mathematically.
> For example, when you want to get the intersection of a ray and a sphere
> you take the function of a line representing the ray and the function
> of the spherical surface, make them equal and solve where they get the
> same value. See http://povray.org/documentation/view/116/ for an
> example implementation of this.
>
> --
> #macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb
x]
> [1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
> -1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// -
Warp -

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