goodgo-platform/scripts/data/vn-country-polygon.ts

/**
 * Simplified Vietnam mainland polygon for "is this point in VN?" tests.
 *
 * The country has a very long, narrow shape (>1500 km north-south) with
 * neighbours pressing in on the western and northern borders. Bbox-based
 * filtering (the chunks the Overpass sync uses) inevitably catches some
 * `landuse=industrial` polygons that sit just across the border in Laos,
 * Cambodia, Thailand and southern China.
 *
 * The polygon below is a hand-traced ~30-vertex outline that follows the
 * official border closely enough for a point-in-polygon test. It's not
 * survey-grade — coastal islands are clipped, and the Mekong delta tip
 * is rounded — but it's sufficient to reject industrial sites that are
 * clearly not in VN. Where edge cases exist (a row landing in the
 * 1-2 km buffer near a border crossing), admin can promote / unlock by
 * hand from the OSM review queue.
 *
 * Format: GeoJSON Polygon, coordinates as `[lng, lat]` pairs (per the
 * spec). The ring is closed (first === last).
 */

import type { Polygon } from 'geojson';

export const VN_COUNTRY_POLYGON: Polygon = {
  type: 'Polygon',
  coordinates: [
    [
      // Northern border, west → east. The northern edge is the actual
      // China border line; we trace it loosely.
      [102.14, 22.47], // Lai Châu / China junction
      [103.0, 22.78], // Lào Cai
      [104.0, 22.82], // northern Hà Giang
      [105.32, 23.39], // Đồng Văn (northernmost point)
      [106.55, 22.95], // Cao Bằng
      [107.0, 22.34], // Lạng Sơn
      [108.05, 21.55], // Móng Cái / Quảng Ninh
      // Eastern boundary at 110°E — generous on the sea side so that
      // every coastal industrial zone (Vũng Áng / Formosa, Dung Quất,
      // Nhơn Hội, Vũng Tàu, Long Sơn etc.) sits inside. This omits the
      // Hoàng Sa / Trường Sa archipelagos — fine, they have no KCN.
      [110.0, 21.0],
      [110.0, 18.0],
      [110.0, 15.0],
      [110.0, 12.0],
      [110.0, 9.5],
      // Mekong delta — Cà Mau cape, then Hà Tiên (south-west tip).
      [105.5, 8.4], // south of Cà Mau
      [104.83, 8.59], // Cà Mau
      [104.45, 10.39], // Hà Tiên
      // West / south-west, climbing along the Cambodia + Laos borders.
      [105.0, 10.78], // Châu Đốc
      [105.85, 11.38], // Tây Ninh
      [106.0, 11.7],
      [106.6, 11.95], // Lộc Ninh
      [107.55, 12.36], // Bù Đăng
      [107.55, 14.42], // Kon Tum
      [107.32, 16.0], // A Lưới
      [106.5, 16.45], // Hướng Hóa
      [105.97, 17.69], // Quảng Bình border
      [105.18, 18.66], // Hà Tĩnh / Laos border
      [104.34, 19.7], // Nghệ An / Laos
      [103.95, 20.66], // Mai Châu
      [103.05, 21.13], // Sơn La / Laos
      [102.78, 21.91], // Điện Biên
      [102.14, 22.47], // close ring
    ],
  ],
};

/** GeoJSON string ready to feed to PostGIS `ST_GeomFromGeoJSON`. */
export const VN_COUNTRY_POLYGON_GEOJSON = JSON.stringify(VN_COUNTRY_POLYGON);

/**
 * Pure-JS point-in-polygon test using the standard ray-casting algorithm.
 * Avoids pulling in `@turf/boolean-point-in-polygon` for the sync script
 * (one fewer dep, and we only have one polygon to test against).
 */
export function isPointInVietnam(lng: number, lat: number): boolean {
  const ring = VN_COUNTRY_POLYGON.coordinates[0];
  let inside = false;
  for (let i = 0, j = ring.length - 1; i < ring.length; j = i++) {
    const xi = ring[i][0];
    const yi = ring[i][1];
    const xj = ring[j][0];
    const yj = ring[j][1];
    const intersect =
      yi > lat !== yj > lat &&
      lng < ((xj - xi) * (lat - yi)) / (yj - yi) + xi;
    if (intersect) inside = !inside;
  }
  return inside;
}