Construction of initial proximity graph from the skeleton graph.

<p>Each skeleton arc is corresponding to a proximity edge in the constructed proximity graph. There was a one-to-one correspondence between building and building node and a one-to-<i>n</i> (<i>n</i> ≧1) correspondence between boundary line segment and boundary node in the graph. The number of the boundary nodes on each boundary segment depends on the number of involved proximity relationships.