Class: RelateNodeGraph


new RelateNodeGraph()

Implements the simple graph of Nodes and EdgeEnd which is all that is required to determine topological relationships between Geometries. Also supports building a topological graph of a single Geometry, to allow verification of valid topology.

It is not necessary to create a fully linked PlanarGraph to determine relationships, since it is sufficient to know how the Geometries interact locally around the nodes. In fact, this is not even feasible, since it is not possible to compute exact intersection points, and hence the topology around those nodes cannot be computed robustly. The only Nodes that are created are for improper intersections; that is, nodes which occur at existing vertices of the Geometries. Proper intersections (e.g. ones which occur between the interior of line segments) have their topology determined implicitly, without creating a Node object to represent them.




Insert nodes for all intersections on the edges of a Geometry. Label the created nodes the same as the edge label if they do not already have a label. This allows nodes created by either self-intersections or mutual intersections to be labelled. Endpoint nodes will already be labelled from when they were inserted.

Precondition: edge intersections have been computed.



Copy all nodes from an arg geometry into this graph. The node label in the arg geometry overrides any previously computed label for that argIndex. (E.g. a node may be an intersection node with a computed label of BOUNDARY, but in the original arg Geometry it is actually in the interior due to the Boundary Determination Rule)