feat: initialize mini program map engine

miniprogram/utils/projection.ts

@@ -0,0 +1,61 @@
+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,
+  }
+}