Tuesday, May 17, 2011  metric rectification from circles  The
circular points encode the metric structure of the 2D plane.
They are invariant to rotation, isotropic scaling and
translation. If the plane undergoes a more general (e.g. affine
or projective) transformation  they move to some unknown
location. Metric rectification can be performed if we find the
image of the circular points and move them back to their
original location. These points are not directly visible in the
image but can be indirectly found using for instance the images
of right angles [HZ].  The circular points can also be extracted
from the images of two circles [IC]. Any two circles in general
position intersect at two possibly complex points.
Interestingly, if we allow points at infinity there are two
additional intersection points: the circular points (1,i,0) and
(1,-i,0), which belong to all circles. If the plane suffers a
projective transformation the circles become general conics (in
a perspective view with the circles in front of