This module compares the clamped cubic B-spline, local cubic Bézier, and piecewise-quintic smoothers against the raw Hybrid A* coarse path. It is an offline developer analysis tool; it does not alter coarse-path search acceptance.

Units and coordinates

All path positions, lengths, clearances, and collision-check spacing use meters. Heading uses radians and vehicle curvature uses 1/m. Map construction retains its existing millimeter input contract; PlanningGridMap provides the meter-coordinate world queries used by smoothing. A smoothing result preserves the coarse path's first and last pose, rather than the original requested goal pose, so its endpoint error is inherited from the coarse planner's accepted goal tolerance.

Facade usage

Only smooth a successful coarse result. A minimal formal call flow is:

if (coarseResult.PlanningResult.Status != PlanningStatus.Success)
    return;
var smoothing = new PathSmoothingService().Smooth(
    new PathSmoothingRequest(
        coarseResult.PlanningResult.Path,
        coarseResult.PlanningResult.Segments,
        coarseResult.MapResult.Map,
        job.Vehicle,
        smoothingConfiguration),
    cancellationToken);
if (smoothing.Status == PathSmoothingStatus.Success ||
    smoothing.Status == PathSmoothingStatus.FallbackToCoarsePath)
    ConsumeSpatialReference(smoothing.Path, smoothing.Segments);

Status handling and fallback

Success supplies a validated smoothed path. FallbackToCoarsePath is an explicit, safe degraded result and may be consumed by the same downstream spatial-reference interface. Infeasible, InvalidInput, Failed, and Cancelled must not be treated as a path. Comparison reports keep an infeasible candidate's markers for diagnosis but never select it as a recommendation.

Fixture freshness

The eight fast fixtures are snapshots of successful coarse paths. Their configuration fingerprint is checked before use. After deliberately changing a scenario or planning configuration, regenerate them with generate_path_smoothing_fixtures.ps1 -Overwrite, then run verify_path_smoothing_fixtures.ps1. Fixture-only comparison never runs Hybrid A*.

IEEE colors, fonts, and Windows PNG

SVG and PNG use the shared IEEE-style colors, status-bearing legends, coordinate ticks, and units. Every raw or smoothed trajectory is rendered as its complete set of discrete samples: reports intentionally draw no line segment between adjacent samples. The Windows PNG renderer requires the exact SimSun and Times New Roman font families and writes a 600 dpi raster image. If either font is unavailable, export returns FontUnavailable; it does not substitute a different font. PNG rendering relies on Windows GDI+, while SVG and CSV remain available without it. SVG uses text-family references, so portable publication requires checking the target font installation or converting text to paths in an external publishing tool.

SQP boundary

This module is geometric smoothing and full-body validation, not sequential quadratic programming (SQP) trajectory optimization. It has no time parameterization, velocity, acceleration, steering-rate, or dynamic-obstacle constraints. Feed only its validated spatial reference into any later SQP or time-parameterization stage.

Output files

run_path_smoothing_comparison.ps1 writes developer reports only below ClumsyPilot/obj/path_smoothing_reports. Each scenario directory contains one comparison.csv and both SVG and 600 dpi PNG versions of these six focused figures:

01-coarse-path-overview — the Hybrid A* coarse-path planning view with map, start, and goal.
02-all-paths-comparison — raw and all three smoother point clouds only, without map or endpoint decorations.
03-cubic-bspline-overview — faded coarse reference and cubic B-spline result with map context.
04-local-cubic-bezier-overview — faded coarse reference and local cubic Bézier result with map context.
05-piecewise-quintic-overview — faded coarse reference and piecewise-quintic result with map context.
06-curvature-comparison — all available curvature samples with s (m) and κ (m⁻¹) axes.

Overhead figures preserve equal X/Y scale and use trajectory-focused bounds; their coordinate ticks are in metres. Inspect the SVG/PNG visually, retain CSV for numerical review, and use an external PDF/EPS publishing step if the final venue requires those formats.