Beier and Chen [23] introduced the concept of a highlight line where a set of points on a surface are determined such
that the distance between a linear light source and an extended
surface normal at the highlight lines is zero (see
Fig. 8.2). Let us denote the linear light source
by
(8.4)
where
is a point on the linear light source,
is a
directional vector and
is a parameter. Also let us define the
extended surface normal vector
at the surface point
by
(8.5)
where
is the surface normal vector at
and
is a parameter. The distance between the two lines
and
is given by
(8.6)
This distance
will vanish if point
is on the highlight
line. If we avoid cases such that the linear light source and the
surface normal become parallel, the denominator of
(8.6) is nonzero and the governing equation for
determining highlight lines reduces to
(8.7)
Equation (8.7) can be traced using the same
technique that we introduced in Sect. 5.8.1. Sone
and Chiyokura [401] developed a method to control a hightlight
line directly using a NURBS boundary Gregory patch. Zhang and Cheng
[460] studied a method to remove local irregularities of
NURBS surface patches by modifying its highlight lines for real time
interactive design.
Figure 8.2:
Definition of highlight line (adapted from
[23])
Next: 8.1.3 Second-order interrogation methods
Up: 8.1.2 First-order interrogation methods
Previous: 8.1.2.3 Reflection lines
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December 2009