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8.1.2.2 Isophotes
Isophotes are curves of constant light intensity on a surface,
created by a point light source at infinity with direction l
(
), specified by the user. These curves can be used for
the detection of surface irregularities
[319,144]. An isophote is a curve
for which the quantity
(8.2)
is constant and equal to
, for
and
where
is the unit
surface normal vector. When the surface is locally planar (or flat)
all normals are parallel and the isophotes do not generally exist. If the
surface is
continuous then the isophote line will be
continuous. For rendering isophotes, the values of
are computed on a lattice and a number of isophotes are
generated by connecting points of equal value found by interpolation
between straddling grid points [3]. Color Plate
A.1 shows isophotes of the bicubic B-spline surface in
Fig.
8.1 with
.
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Up: 8.1.2 First-order interrogation methods
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December 2009