@technobuddha/library/dist/is-point-in-polygon.js

A large library of useful functions

import { isPointOnLineSegment } from "./is-point-on-line-segment.js";
import { toLineSegment } from "./to-line-segment.js";
/**
 * Determines whether a given point is inside or on the edge of a polygon.
 *
 * @param point - The point to test, represented as a Cartesian coordinate.
 * @param polygon - The polygon to test against, represented as an array of Cartesian coordinates.
 * @returns `true` if the point is inside the polygon or on its edge, otherwise `false`.
 *
 * @remarks
 * - The polygon is assumed to be a simple, non-self-intersecting polygon.
 * - Points on the edge of the polygon return `true`.
 * - Uses ray-casting algorithm with explicit edge detection.
 *
 * @group Geometry
 * @category Polygon
 * @category Point
 */
export function isPointInPolygon(point, polygon) {
    if (polygon.length < 3) {
        return false;
    }
    // First check if point is on any edge
    for (let i = 0; i < polygon.length; i++) {
        const p1 = polygon[i];
        const p2 = polygon[(i + 1) % polygon.length];
        if (isPointOnLineSegment(point, toLineSegment(p1, p2))) {
            return true;
        }
    }
    // Use ray-casting algorithm for interior points
    let inside = false;
    for (let i = 0, j = polygon.length - 1; i < polygon.length; j = i++) {
        const pi = polygon[i];
        const pj = polygon[j];
        if (pi.y > point.y !== pj.y > point.y &&
            point.x < ((pj.x - pi.x) * (point.y - pi.y)) / (pj.y - pi.y) + pi.x) {
            inside = !inside;
        }
    }
    return inside;
}
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