10
A More Robust Approach
Using only 3 points is dangerous, because if even one
is
off, the transformation can be far from correct.
Instead,
use many (n =10 or more) pairs of
matching
control
points to determine a least squares estimate
of
the
six parameters of the affine transformation.
Error(a11,
a12, a13, a21, a22, a23) =
å
((a11*xj + a12*yj + a13 - uj)
+
(a21*xj + a22*yj + a23
- vj) )
j=1,n
2
2