Line merging that respects line direction

[dr-jts]

JTS provides the LineMerger class to merge contiguous LineStrings together. It treats the lines as an undirected graph, and flips the direction of lines if needed to merge them.

PostGIS-4939 requests an "directional" form of line merging which respects line direction (i.e. treats the input lines as a directed graph). Only lines which can be joined with no change in direction are merged.

This will likely use a simpler algorithm than the existing LineMerger. So it may make sense to implement as a separate class, rather than as an option to the existing class. Perhaps LineMergerDirected?

Example

• Input: MULTILINESTRING((-29 -27,1 2),(-29 -27,-45 -33),(-45 -33,-46 -32))
• Output
  • LineMerger: LINESTRING(1 2,-29 -27,-45 -33,-46 -32)
  • directional line merging: MULTILINESTRING((-29 -27,1 2),(-29 -27,-45 -33,-46 -32))