Merge pull request #4369 from Leaflet/use-mean-earth-radius

Use mean earth radius for distance calculation in L.CRS.Earth.

spec/suites/geo/CRSSpec.js

@@ -197,3 +197,15 @@ describe("CRS.ZoomNotPowerOfTwo", function () {
 		});
 	});
 });
+
+describe("CRS.Earth", function () {
+	describe("#distance", function () {
+		// Test values from http://rosettacode.org/wiki/Haversine_formula,
+		// we assume using mean earth radius (https://en.wikipedia.org/wiki/Earth_radius#Mean_radius)
+		// is correct, since that's what International Union of Geodesy and Geophysics recommends,
+		// and that sounds serious.
+		var p1 = L.latLng(36.12, -86.67);
+		var p2 = L.latLng(33.94, -118.40);
+		expect(L.CRS.Earth.distance(p1, p2)).to.be.within(2886444.43, 2886444.45);
+	});
+});

src/geo/crs/CRS.Earth.js

@@ -5,7 +5,10 @@
 L.CRS.Earth = L.extend({}, L.CRS, {
 	wrapLng: [-180, 180],
 
-	R: 6378137,
+	// Mean Earth Radius, as recommended for use by
+	// the International Union of Geodesy and Geophysics,
+	// see http://rosettacode.org/wiki/Haversine_formula
+	R: 6371000,
 
 	// distance between two geographical points using spherical law of cosines approximation
 	distance: function (latlng1, latlng2) {