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Section 12.4 Notes 390

to unknown scale.
(a) Show that three points is a frame group.
(b) Show that a vertex-pair (two points, with a pair of directions leaving one
of the points) is a frame group.
(c) Show that a line and a point is not a frame group.
(d) Explain why it is a good idea to have frame groups composed of different
types of feature.

PROGRAMMING EXERCISES
12.7. Build a robust iterated closest points matcher, and use it to match plane curves
(for example, the edges of a letter to an instance of the letter; see Figure 1
of Fitzgibbon (2003)). You will find it helpful to read Fitzgibbon (2003), which
shows that second-order methods can be used quite effectively, even though
the objective function isn’t differentiable.
12.8. Use one of the available sets of software for active appearance model matching
to build an active appearance model of a face and then match it to a deformed
face image.