On Mon, 14 Jan 2002 14:31:59 -0800, Dearmad <dea### [at] applesnakenet>
wrote:

>no, they'll intersect.  I meant to say the light should be
>slightly *larger* than the cone so that the cone is sure to be
>hit by the matching light.

A cone is defined as the locus of all lines passing through a point
(vertex) and forming the same angle with a given line (the axis) also
passing through above point. Another way to define a cone is to rotate
a line (ruler) about another line (axis), whereas the two lines
intersect, and the surface formed by above rotation (ruled surface, in
this case also surface of revolution) is a cone.

You can easily see that if you place your cone so that the vertex is
at the location of the light source, be it point or spot, the rays of
light will be either inside the cone, outside the cone or coincident
with it. The latter is highly unlikely due to numeric inaccuracies
inherent to the way computers treat floating point numbers, so in
practice no way will intersect the cone's surface (except the base),
and that's what really counts in raytracing.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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