https://sanderd17.github.io/geoHelpers.js

1var geoHelper = (function()
2{
3	/**
4	 * Calculate the distance between two coordinates
5	 * @returns the spherical distance in meters 
6	 */
7	var getDistance = function (co1, co2)
8	{
9		if (!co1.lat || !co2.lat || !co1.lon || !co2.lon)
10			return -1;
11		var R = 6.371e6; // average radius of the earth in m
12		var dLat = (co2.lat-co1.lat) * Math.PI/180;
13		var dLon = (co2.lon-co1.lon) * Math.PI/180; 
14		var a = 
15			0.5 - Math.cos(dLat)/2 +
16			(0.5 - Math.cos(dLon)/2) *
17			Math.cos(co1.lat * Math.PI/180) *
18			Math.cos(co2.lat * Math.PI/180);
19		return R * 2 * Math.asin(Math.sqrt(a)); // Distance in m
20	};
21
22	/**
23	 * Transform latitude, longitude and zoom to tile coordinates
24	 */
25	var latlonToTilenumber = function (lat, lon, zoom)
26	{
27		var n = Math.pow(2, zoom);
28		var lat_rad = lat * Math.PI / 180;
29		return {
30			"x": Math.floor(n * ((lon + 180) / 360)), 
31			"y": Math.floor(n * (1 - (Math.log(Math.tan(lat_rad) + 1/Math.cos(lat_rad)) / Math.PI)) / 2) }
32	};
33
34	var tilenumberToBbox = function (x, y, zoom)
35	{
36		var northWest = tilenumberToLatlon(x, y, zoom);
37		var southEast = tilenumberToLatlon(x + 1, y + 1, zoom);
38		return {
39			"t" : northWest.lat,
40			"b" : southEast.lat,
41			"l" : northWest.lon,
42			"r" : southEast.lon,
43		};
44	};
45
46	var tilenumberToLatlon = function(x, y, zoom)
47	{
48		var n = Math.PI - (2.0 * Math.PI * y) / Math.pow(2.0, zoom);
49		return {
50			"lat": Math.atan(Math.sinh(n)) *180 / Math.PI,
51			"lon": x / Math.pow(2, zoom) * 360.0 - 180
52		};
53	};
54
55	var padBbox = function (bbox, distance)
56	{
57		var corners =
58		{
59			"tl": {"lat": bbox.t, "lon": bbox.l},
60			"tr": {"lat": bbox.t, "lon": bbox.r},
61			"bl": {"lat": bbox.b, "lon": bbox.l},
62			"br": {"lat": bbox.b, "lon": bbox.r},
63		};
64		var l = Math.max(
65			getDistance(corners.tl, corners.tr),
66			getDistance(corners.bl, corners.br),
67			getDistance(corners.tl, corners.bl),
68			getDistance(corners.tr, corners.br)
69		);
70		var padding = distance / l;
71		bbox.t += (bbox.t - bbox.b) * padding;
72		bbox.b -= (bbox.t - bbox.b) * padding;
73		bbox.r += (bbox.r - bbox.l) * padding;
74		bbox.l -= (bbox.r - bbox.l) * padding;
75	};
76
77	return {
78		"getDistance": getDistance,
79		"latlonToTilenumber": latlonToTilenumber,
80		"tilenumberToLatlon": tilenumberToLatlon,
81		"tilenumberToBbox": tilenumberToBbox,
82		"padBbox": padBbox,
83	};
84})();