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Suppose we have a line image and
wish to automatically label it. At each vertex
- the labelling must
be one of the permissible ones -- one of a relative small number
- each line segment has two ends, and
it must have the same labelling at each end, at least in the case
of polyhedral models.
Start by taking the outside lines in the
image and label them as occluding the background.
We may now organise our method
as a tree search.
- Choose a junction, label
it in a valid way,
- Move along its edges to neighbouring
junctions, labelling them in a consistent manner.
- If this is not
possible, we must backtrack and try another
alternative for a previous choice.
- Continue until we
have successfully labelled the drawing, or we have no
- In the latter case the line image does not
represent a valid physical object.
Note that more than one valid interpretation may exist, so we may
wish to make our tree search exhaustive to find other permissible
labellings, rather than just stopping after after finding one
consistent labelling for the whole image.
David Marshall 1994-1997