Centerline — Algorithm Notes

Related user page: Centerline

Purpose

Extract a centerline path guided by a raster cost surface and seed-line endpoints.

Inputs: seed line vector, CHM/cost raster, guided strategy (pairwise default), segment-processing options
Outputs: centerline vector and auxiliary corridor/path artifacts

Build/prepare local cost representation from input raster.
Derive graph/candidate route structures for each line context.
Solve the least-cost path with the selected method.
Build the corridor raster and corridor polygon with the selected method.
Extract the centerline from the corridor polygon using the least-cost path as guidance.
Apply endpoint/trim post-processing.
Optionally run geo-simplify reduce-bend on extracted centerlines.
Write centerline and supporting outputs.

bera is the default and preserves the existing BERA Tools workflow: BERA Dijkstra/skimage least-cost path, BERA corridor raster, corridor polygon, then polygon-centerline extraction.
astar uses an 8-neighbor grid A* least-cost path with stable tie-breaking toward the seed-line direction.
The least-cost path can be simplified with geo-simplify reduce-bend --smooth-line and smoothed before corridor generation for either method.
The A corridor raster is built from forward/reverse A accumulation. It uses BERA's corridor convention: 0 inside the corridor and 1 outside.
The A* corridor supports a line-bias weight and a distance-from-path penalty weight.
The corridor polygon can be simplified and smoothed before final centerline extraction for either method.
The A final centerline is derived from the A corridor polygon using the processed A* least-cost path as the guide line.

Default mode is pairwise.
main_route: unguided extraction from the corridor graph; requires post clipping/snapping (trim/snap) to align terminals.
pairwise: endpoint-guided extraction by scoring source/destination node pairs and selecting the best path.
virtual_nodes: endpoint-guided extraction by adding temporary source/destination graph nodes before shortest-path solve.
direct_insert: endpoint-guided extraction by inserting endpoints directly into the Voronoi graph before shortest-path solve.

main_route: most tolerant when endpoint guidance is weak or unavailable; unlike guided modes, it depends on post clipping/snapping to recover line terminals.
pairwise (default): explicit endpoint control with direct pair scoring; favored for general production workflows.
virtual_nodes: graph-augmentation approach that can navigate complex shapes where strict pair matching is limiting.
direct_insert: strongest geometric endpoint anchoring by direct graph insertion; favored when exact terminal placement is critical.

pairwise and main_route are the primary supported modes, exposed through the GUI; all four modes remain available via CLI/API.
virtual_nodes and direct_insert are not exposed in the GUI at this time and may be phased out in a future release.
direct_insert includes a clearance-weight control (snap_clearance_weight) in the implementation; this parameter may be exposed in CLI/API or GUI later.