104 lines
3.2 KiB
TypeScript
104 lines
3.2 KiB
TypeScript
export interface LonLatPoint {
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lon: number
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lat: number
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}
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export interface WebMercatorPoint {
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x: number
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y: number
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}
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export interface WorldTilePoint {
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x: number
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y: number
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}
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const MAX_LATITUDE = 85.05112878
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const EARTH_RADIUS = 6378137
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function clampLatitude(lat: number): number {
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return Math.max(-MAX_LATITUDE, Math.min(MAX_LATITUDE, lat))
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}
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export function lonLatToWebMercator(point: LonLatPoint): WebMercatorPoint {
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const latitude = clampLatitude(point.lat)
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const lonRad = point.lon * Math.PI / 180
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const latRad = latitude * Math.PI / 180
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return {
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x: EARTH_RADIUS * lonRad,
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y: EARTH_RADIUS * Math.log(Math.tan(Math.PI / 4 + latRad / 2)),
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}
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}
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export function webMercatorToLonLat(point: WebMercatorPoint): LonLatPoint {
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return {
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lon: point.x / EARTH_RADIUS * 180 / Math.PI,
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lat: (2 * Math.atan(Math.exp(point.y / EARTH_RADIUS)) - Math.PI / 2) * 180 / Math.PI,
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}
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}
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export function lonLatToWorldTile(point: LonLatPoint, zoom: number): WorldTilePoint {
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const latitude = clampLatitude(point.lat)
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const scale = Math.pow(2, zoom)
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const latRad = latitude * Math.PI / 180
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return {
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x: (point.lon + 180) / 360 * scale,
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y: (1 - Math.log(Math.tan(latRad) + 1 / Math.cos(latRad)) / Math.PI) / 2 * scale,
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}
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}
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export function worldTileToLonLat(point: WorldTilePoint, zoom: number): LonLatPoint {
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const scale = Math.pow(2, zoom)
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const lon = point.x / scale * 360 - 180
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const latRad = Math.atan(Math.sinh(Math.PI * (1 - 2 * point.y / scale)))
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return {
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lon,
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lat: latRad * 180 / Math.PI,
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}
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}
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const CHINA_AXIS = 6378245
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const CHINA_EE = 0.00669342162296594323
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function isOutsideChina(point: LonLatPoint): boolean {
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return point.lon < 72.004 || point.lon > 137.8347 || point.lat < 0.8293 || point.lat > 55.8271
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}
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function transformLat(x: number, y: number): number {
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let result = -100 + 2 * x + 3 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x))
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result += (20 * Math.sin(6 * x * Math.PI) + 20 * Math.sin(2 * x * Math.PI)) * 2 / 3
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result += (20 * Math.sin(y * Math.PI) + 40 * Math.sin(y / 3 * Math.PI)) * 2 / 3
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result += (160 * Math.sin(y / 12 * Math.PI) + 320 * Math.sin(y * Math.PI / 30)) * 2 / 3
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return result
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}
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function transformLon(x: number, y: number): number {
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let result = 300 + x + 2 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x))
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result += (20 * Math.sin(6 * x * Math.PI) + 20 * Math.sin(2 * x * Math.PI)) * 2 / 3
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result += (20 * Math.sin(x * Math.PI) + 40 * Math.sin(x / 3 * Math.PI)) * 2 / 3
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result += (150 * Math.sin(x / 12 * Math.PI) + 300 * Math.sin(x / 30 * Math.PI)) * 2 / 3
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return result
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}
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export function gcj02ToWgs84(point: LonLatPoint): LonLatPoint {
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if (isOutsideChina(point)) {
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return point
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}
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const dLat = transformLat(point.lon - 105, point.lat - 35)
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const dLon = transformLon(point.lon - 105, point.lat - 35)
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const radLat = point.lat / 180 * Math.PI
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const magic = Math.sin(radLat)
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const sqrtMagic = Math.sqrt(1 - CHINA_EE * magic * magic)
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const latOffset = (dLat * 180) / ((CHINA_AXIS * (1 - CHINA_EE)) / (sqrtMagic * sqrtMagic * sqrtMagic) * Math.PI)
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const lonOffset = (dLon * 180) / (CHINA_AXIS / sqrtMagic * Math.cos(radLat) * Math.PI)
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return {
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lon: point.lon - lonOffset,
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lat: point.lat - latOffset,
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}
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}
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