In image processing line labelling classifies lines depending on whether they represent the internal edges between faces of an object or the external edges where one object obscures another. Waltz's algorithm is one approach to this. Line labelling follows edge detection in a classic image processing pipeline.
Used in Chap. 12: pages 188, 190, 202
Applying Waltz's algorithm: Pass 1: Label the lines at the boundary of the scene; Pass 2: Find vertices where the currently labelled lines are sufficient to
determine the type of the vertex; Pass 3: Label the rest of the lines from those vertices accordingly.