Sketch to Orthogonal Polygon

Turn a FREEHAND RECTILINEAR SKETCH into an EXACT ORTHOGONAL POLYGON, or refuse. Zero runtime dependencies.

THE SILENT FAILURE. A user sketches a floor plan or a room outline by hand -- mouse, finger or stylus -- and the app converts the stroke into a polygon it will then compute AREA, WALL LENGTH and MATERIAL QUANTITIES from. Every failure mode below produces a polygon that RENDERS CONVINCINGLY ON SCREEN AND MEASURES WRONG. Nothing crashes. Nothing throws. The number that comes out looks exactly like a real area, because it is a real number, computed by a real formula, from the wrong shape.

THE NEARLY-CLOSED LOOP. The pen's last point lands a few pixels from its first. Treating the stroke as closed and treating it as open give different polygons and different areas, and at sketch resolution the two are visually identical.

The others are the same shape of problem: a segment that is nearly-but-not-quite axis-aligned, a doubled vertex from a slow hand, a self-touching corner. Each is a small numeric decision, each has a defensible default, and each silently changes what the customer is quoted.

SO IT IS ALLOWED TO REFUSE. A stroke whose intended shape is genuinely ambiguous returns a refusal naming the ambiguity, rather than the nearest plausible rectangle -- because the output of this feeds a quote, and a confident wrong area is billed.

VERIFIED: 53 tests, measured by running the suite.

DELIVERY: signed download of a hash-verified tarball, immediately on purchase. Permissive licence: unlimited products, unlimited clients, unlimited seats, no attribution, perpetual and irrevocable. One restriction, do not republish the source as source.

Interface

What you call, and what comes back. Types and signatures only — the implementation ships with the source.

  export function distance(a: Point, b: Point): number;
  export function signedArea(polygon: Point[]): number;
  export function polygonArea(polygon: Point[]): number;
  export function normalizeWinding(polygon: Point[]): WindingNormalization;
  export function segmentsIntersect(p1: Point, p2: Point, p3: Point, p4: Point): boolean;
  export function isSelfIntersecting(polygon: Point[]): boolean;
  export function simplifyPolyline(points: Point[], tolerance: number): Point[];
  export function sketchToOrthogonalPolygon(stroke: Point[], options: SketchOptions): SketchOutcome;
  export function angleToNearestAxis(dx: number, dy: number): AxisSnapInfo;

  export type AxisKind = 'horizontal' | 'vertical';
  export type SketchOutcome = OrthogonalPolygonResult | OrthogonalPolygonRefusal;