JavaScript mercator projection

project.js

/*jslint vars: true */
// adapted from http://wiki.openstreetmap.org/wiki/Mercator#JavaScript

(function () {
	var project = {};
	
	if (typeof exports === "object") {
		module.exports = project;
	} else {
		this.project = project;
	}
	
	var DegRad = Math.PI / 180,
		RMax = 6378137,
		RMin = 6356752.3142,
		LatMin = -89.5,
		LatMax = 89.5,
		Eccent = Math.sqrt(1 - ((RMin / RMax) * (RMin / RMax)));
	
	function rad(x) {
		return x * DegRad;
	}
	
	function mercLng(lng) {
		return RMax * rad(lng);
	}
	
	function mercLat(lat) {
		if (lat > LatMax) {
			lat = LatMax;
		}
		if (lat < LatMin) {
			lat = LatMin;
		}
		var phi = rad(lat),
			con = Eccent * Math.sin(phi),
			com = 0.5 * Eccent,
			ts;
		con = Math.pow((1 - con) / (1 + con), com);
		ts = Math.tan(0.5 * (Math.PI * 0.5 - phi)) / con;
		return -(RMax * Math.log(ts));
	}
	
	function fitLat(lat, height, latMin, latMax) {
		latMin = latMin || LatMin;
		latMax = latMax || LatMax;
		var mercLatMin = mercLat(latMin),
			mercLatMax = mercLat(latMax),
			mercLatHeight = -mercLatMin + mercLatMax;
		return (mercLatMax - lat) * (height / mercLatHeight);
	}
	
	function fitLng(lng, width, lngMin, lngMax) {
		var mercLngMin = mercLng(lngMin);
		return (lng + mercLngMin) * (width / (-mercLngMin + mercLng(lngMax)));
	}
	
	function mercatorRatio(latMin, latMax, lngMin, lngMax) {
		var width = -mercLng(lngMin) + mercLng(lngMax),
			height = -mercLat(latMin) + mercLat(latMax);
		return width / height;
	}
	project.mercatorRatio = mercatorRatio;
	
	function mercator(width, height, latMin, latMax, lngMin, lngMax, latLng) {
		var x = fitLng(mercLng(last(latLng)), width, lngMin, lngMax),
			y = fitLat(mercLat(head(latLng)), height, latMin, latMax);
		return [x, y];
	}
	project.mercator = mercator;
}());