Mercator Projection for Google Maps JS SDK

Mercator Projection.js

// Base tile size used in Google Javascript SDK
const GOOGLE_BASE_TILE_SIZE = 256;

// MercatorProjection implements the Projection interface defined in Google Maps
// Javascript SDK.
//
// Google Maps Javascript SDK docs:
// https://developers.google.com/maps/documentation/javascript/maptypes#WorldCoordinates
//
// For more details about the convertions see
// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
class MercatorProjection {
  constructor(googleMaps) {
    this.googleMaps = googleMaps;
  }

  fromLatLngToPoint(coord) {
    let siny = Math.sin(coord.lat() * Math.PI / 180);

    // Truncating to 0.9999 effectively limits latitude to 89.189. This is
    // about a third of a tile past the edge of the world tile.
    siny = Math.min(Math.max(siny, -0.9999), 0.9999);

    return new this.googleMaps.Point(
      GOOGLE_BASE_TILE_SIZE * (0.5 + coord.lng() / 360),
      GOOGLE_BASE_TILE_SIZE * (0.5 - Math.log((1 + siny) / (1 - siny)) / (4 * Math.PI)),
    );
  }

  fromPointToLatLng(point) {
    let n = Math.PI * (1 - 2 * point.y / GOOGLE_BASE_TILE_SIZE);

    return new this.googleMaps.LatLng(
      Math.atan(0.5 * (Math.exp(n) - Math.exp(-n))) * (180 / Math.PI),
      point.x / GOOGLE_BASE_TILE_SIZE * 360.0 - 180.0,
    );
  }
}

Thanks for this code. However can you explain when y = 0, lat = 85.1.

Sorry, I found out why. Please ignore my question.