Waltz Filtering Process

  1. Associate with each vertex a set of all possible labels for that vertex type.

  2. Compare the label sets along lines: a label for a line must be consistent at both ends. If a vertex label involves a line label that cannot be matched at the other end, that vertex label can be deleted.

  3. As vertex labels are deleted, see if other vertices adjacent along some line are further constrained.

  4. Continue until no further deletions are possible.

  5. Search in the reduced label set for globally consistent interpretations.
The constraint propagation rapidly reduces the size of the search space of possible interpretations: each time a node label is deleted, the branching factor of the search at that node is reduced by one.

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