leaflet/src/geo/projection/Projection.Mercator.js

JavaScript library for mobile-friendly interactive maps

import {LatLng} from '../LatLng.js';
import {Bounds} from '../../geometry/Bounds.js';
import {Point} from '../../geometry/Point.js';

/*
 * @namespace Projection
 * @projection Projection.Mercator
 *
 * Elliptical Mercator projection — more complex than Spherical Mercator. Assumes that Earth is an ellipsoid. Used by the EPSG:3395 CRS.
 */

const earthRadius = 6378137;

export const Mercator = {
	R: earthRadius,
	R_MINOR: 6356752.314245179,

	bounds: new Bounds([-20037508.34279, -15496570.73972], [20037508.34279, 18764656.23138]),

	project(latlng) {
		latlng = new LatLng(latlng);
		const d = Math.PI / 180,
		r = this.R,
		tmp = this.R_MINOR / r,
		e = Math.sqrt(1 - tmp * tmp);
		let y = latlng.lat * d;
		const con = e * Math.sin(y);

		const ts = Math.tan(Math.PI / 4 - y / 2) / ((1 - con) / (1 + con)) ** (e / 2);
		y = -r * Math.log(Math.max(ts, 1E-10));

		return new Point(latlng.lng * d * r, y);
	},

	unproject(point) {
		point = new Point(point);
		const d = 180 / Math.PI,
		r = this.R,
		tmp = this.R_MINOR / r,
		e = Math.sqrt(1 - tmp * tmp),
		ts = Math.exp(-point.y / r);
		let phi = Math.PI / 2 - 2 * Math.atan(ts);

		for (let i = 0, dphi = 0.1, con; i < 15 && Math.abs(dphi) > 1e-7; i++) {
			con = e * Math.sin(phi);
			con = ((1 - con) / (1 + con)) ** (e / 2);
			dphi = Math.PI / 2 - 2 * Math.atan(ts * con) - phi;
			phi += dphi;
		}

		return new LatLng(phi * d, point.x * d / r);
	}
};