B. Epipolar Geometry
The projective geometry between two views of a scene is
completely described by the epipolar geometry. In other words,
the epipolar geometry is the intrinsic geometry of two views.
It has important applications in stereo matching as it limits the
search for correspondence into a one-dimensional search space.
Consider a point in 3-D that is imaged in two views. In
the first view, its image is point , while in the second view, its
image is . For a typical stereo matching problem, we have the
point in one image and wish to find its correspondence in
another image. We observe that both camera centers and ,
the points , , and are coplanar. This plane is the epipolar
plane . The line that connects the two camera centers is called
the baseline. The points and where the baseline intersects
the two views are called epipoles. The lines connecting , and
, are the epipolar lines. From the definition of perspective
projection, we know that the points , , and are collinear
and that any point on this line between and projects as in
the first image. Therefore, we see that the correspondence of
must lie on the projection of the line from to in the second
image. An illustration of epipolar geometry is shown in Fig. 2.