planar-geometry-kit

Small, dependency-free 2D computational-geometry helpers, plus a haversine great-circle distance for the occasional geo problem.

Points are [x, y] tuples. Polygons are arrays of points in either winding order (functions that care about orientation say so).

Install

npm install planar-geometry-kit

Usage

const geom = require("planar-geometry-kit");

geom.distance([0, 0], [3, 4]);                       // 5
geom.area([[0, 0], [4, 0], [0, 3]]);                 // 6  (triangle)
geom.centroid([[0, 0], [2, 0], [2, 2], [0, 2]]);     // [1, 1]
geom.pointInPolygon([2, 2], [[0,0],[4,0],[4,4],[0,4]]); // true
geom.convexHull([[0,0],[4,0],[4,4],[0,4],[2,2]]);    // the 4 corners
geom.haversine([0, 0], [0, 1]);                      // ~111.19 km

API

Points and segments:

• distance(a, b), distanceSquared(a, b), midpoint(a, b)
• cross(a, b, c) — signed cross product; orientation test
• onSegment(p, q, r) — is q on the collinear segment p-r?
• segmentsIntersect(p1, p2, p3, p4) — includes touching/collinear cases

Polygons:

• signedArea(poly) / area(poly) — shoelace formula
• perimeter(poly)
• centroid(poly) — area-weighted, with a vertex-average fallback for zero-area input
• pointInPolygon(point, poly) — ray casting; boundary points count as inside
• convexHull(points) — Andrew's monotone chain, CCW order

Spherical:

• haversine(a, b, radius = EARTH_RADIUS_KM) — [lat, lon] in degrees → distance
• EARTH_RADIUS_KM — IUGG mean radius (6371.0088 km)

License

MIT