Add the haversine formula (#194)

Author: fuslonflare

Algorithms.Tests/Other/GeoLocationTests.cs

@@ -0,0 +1,24 @@
+using System;
+
+using Algorithms.Other;
+
+using NUnit.Framework;
+using NUnit.Framework.Internal;
+
+namespace Algorithms.Tests.Other
+{
+    public static class GeoLocationTests
+    {
+        [Test]
+        [TestCase(53.430488d, -2.96129d, 53.430488d, -2.96129d, 0d)]
+        [TestCase(53.430971d, -2.959806d, 53.430242d, -2.960830d, 105d)]
+        public static void CalculateDistanceFromLatLngTest(double lat1, double lng1, double lat2, double lng2, double expectedValue)
+        {
+            var result = GeoLocation.CalculateDistanceFromLatLng(lat1, lng1, lat2, lng2);
+            var actualValue = Convert.ToDouble(result);
+
+            // Assert
+            Assert.AreEqual(expectedValue, actualValue, 1d); // Accept if distance diff is +/-1 meters.
+        }
+    }
+}

Algorithms/Other/GeoLocation.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Algorithms.Other
+{
+    public static class GeoLocation
+    {
+        private const double EarthRadiusKm = 6371.01d;
+
+        /// <summary>
+        /// Calculates spherical distance between 2 points given their latitude, longitude coordinates. https://www.movable-type.co.uk/scripts/latlong.html.
+        /// </summary>
+        /// <param name="lat1">Latitude of point A.</param>
+        /// <param name="lng1">Longitude of point A.</param>
+        /// <param name="lat2">Latitude of point B.</param>
+        /// <param name="lng2">Longitude of point B.</param>
+        /// <returns>Spherical distance between A and B.</returns>
+        public static double CalculateDistanceFromLatLng(double lat1, double lng1, double lat2, double lng2)
+        {
+            var pi180 = Math.PI / 180d;
+            var lat1Radian = lat1 * pi180;
+            var lng1Radian = lng1 * pi180;
+            var lat2Radian = lat2 * pi180;
+            var lng2Radian = lng2 * pi180;
+
+            var diffLat = lat2Radian - lat1Radian;
+            var diffLng = lng2Radian - lng1Radian;
+
+            var haversine = Math.Sin(diffLat / 2) * Math.Sin(diffLat / 2) + Math.Cos(lat1Radian) * Math.Cos(lat2Radian) * Math.Sin(diffLng / 2) * Math.Sin(diffLng / 2);
+            var distance = EarthRadiusKm * (2d * Math.Atan2(Math.Sqrt(haversine), Math.Sqrt(1 - haversine)));
+
+            return distance * 1000; // Convert from km -> m
+        }
+    }
+}