mini-prog/miniprogram/utils/projection.ts

export interface LonLatPoint {
  lon: number
  lat: number
}

export interface WebMercatorPoint {
  x: number
  y: number
}

export interface WorldTilePoint {
  x: number
  y: number
}

const MAX_LATITUDE = 85.05112878
const EARTH_RADIUS = 6378137

function clampLatitude(lat: number): number {
  return Math.max(-MAX_LATITUDE, Math.min(MAX_LATITUDE, lat))
}

export function lonLatToWebMercator(point: LonLatPoint): WebMercatorPoint {
  const latitude = clampLatitude(point.lat)
  const lonRad = point.lon * Math.PI / 180
  const latRad = latitude * Math.PI / 180

  return {
    x: EARTH_RADIUS * lonRad,
    y: EARTH_RADIUS * Math.log(Math.tan(Math.PI / 4 + latRad / 2)),
  }
}

export function webMercatorToLonLat(point: WebMercatorPoint): LonLatPoint {
  return {
    lon: point.x / EARTH_RADIUS * 180 / Math.PI,
    lat: (2 * Math.atan(Math.exp(point.y / EARTH_RADIUS)) - Math.PI / 2) * 180 / Math.PI,
  }
}

export function lonLatToWorldTile(point: LonLatPoint, zoom: number): WorldTilePoint {
  const latitude = clampLatitude(point.lat)
  const scale = Math.pow(2, zoom)
  const latRad = latitude * Math.PI / 180

  return {
    x: (point.lon + 180) / 360 * scale,
    y: (1 - Math.log(Math.tan(latRad) + 1 / Math.cos(latRad)) / Math.PI) / 2 * scale,
  }
}

export function worldTileToLonLat(point: WorldTilePoint, zoom: number): LonLatPoint {
  const scale = Math.pow(2, zoom)
  const lon = point.x / scale * 360 - 180
  const latRad = Math.atan(Math.sinh(Math.PI * (1 - 2 * point.y / scale)))

  return {
    lon,
    lat: latRad * 180 / Math.PI,
  }
}

const CHINA_AXIS = 6378245
const CHINA_EE = 0.00669342162296594323

function isOutsideChina(point: LonLatPoint): boolean {
  return point.lon < 72.004 || point.lon > 137.8347 || point.lat < 0.8293 || point.lat > 55.8271
}

function transformLat(x: number, y: number): number {
  let result = -100 + 2 * x + 3 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x))
  result += (20 * Math.sin(6 * x * Math.PI) + 20 * Math.sin(2 * x * Math.PI)) * 2 / 3
  result += (20 * Math.sin(y * Math.PI) + 40 * Math.sin(y / 3 * Math.PI)) * 2 / 3
  result += (160 * Math.sin(y / 12 * Math.PI) + 320 * Math.sin(y * Math.PI / 30)) * 2 / 3
  return result
}

function transformLon(x: number, y: number): number {
  let result = 300 + x + 2 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x))
  result += (20 * Math.sin(6 * x * Math.PI) + 20 * Math.sin(2 * x * Math.PI)) * 2 / 3
  result += (20 * Math.sin(x * Math.PI) + 40 * Math.sin(x / 3 * Math.PI)) * 2 / 3
  result += (150 * Math.sin(x / 12 * Math.PI) + 300 * Math.sin(x / 30 * Math.PI)) * 2 / 3
  return result
}

export function gcj02ToWgs84(point: LonLatPoint): LonLatPoint {
  if (isOutsideChina(point)) {
    return point
  }

  const dLat = transformLat(point.lon - 105, point.lat - 35)
  const dLon = transformLon(point.lon - 105, point.lat - 35)
  const radLat = point.lat / 180 * Math.PI
  const magic = Math.sin(radLat)
  const sqrtMagic = Math.sqrt(1 - CHINA_EE * magic * magic)
  const latOffset = (dLat * 180) / ((CHINA_AXIS * (1 - CHINA_EE)) / (sqrtMagic * sqrtMagic * sqrtMagic) * Math.PI)
  const lonOffset = (dLon * 180) / (CHINA_AXIS / sqrtMagic * Math.cos(radLat) * Math.PI)

  return {
    lon: point.lon - lonOffset,
    lat: point.lat - latOffset,
  }
}