gray scale matching:
the pixel distance must be computed as a function of both pixel position and pixel intensity.
Another way to be robust to illumination changes. The alternative is to use correlation.
Feature based model.
match between object feature and image features.
The search is through a tree. Each node in the tree represents a set of matches. Root node represents empty set. Each other node is the union of the matches in the parent node and one additional match.
Hypothesized and Test
This is used for generating a hypothesis about the projection from the object coordinate frame to the image frame.
The hypothesis can b obtained by pose consistency, pose clustering, or by using invariants.