Function GraphOptions.edgeType

Specifies whether the S2Builder input edges should be treated as undirected. If true, then all input edges are duplicated into pairs consisting of an edge and a sibling (reverse) edge. The layer implementation is responsible for ensuring that exactly one edge from each pair is used in the output, i.e. *only half* of the graph edges will be used. (Note that some values of the sibling_pairs() option automatically take care of this issue by removing half of the edges and changing edge_type() to DIRECTED.)