Find Distance between two uk postcodes

using System;  
02.using System.Net;  
03.using System.Web;  
04.using System.Xml;  
05.  
06.namespace Codebrain  
07.{  
08.    public static class Distance  
09.    {  
10.        // Handy structure for Long/Lat information  
11.        public struct Coords  
12.        {  
13.            public double Longitude;  
14.            public double Latitude;  
15.        }  
16.  
17.        // Unit calculations  
18.        public enum Units  
19.        {  
20.            Miles,  
21.            Kilometres  
22.        }  
23.  
24.        // Will return a null if the Google API is unable to find either post code, or the country constraint fails  
25.        public static double? BetweenTwoPostCodes(string postcodeA, string postcodeB, string countryCodeWithin, Units units)  
26.        {  
27.            var ll1 = PostCodeToLongLat(postcodeA, countryCodeWithin);  
28.            if (!ll1.HasValue) return null;  
29.            var ll2 = PostCodeToLongLat(postcodeB, countryCodeWithin);  
30.            if (!ll2.HasValue) return null;  
31.            return ll1.Value.DistanceTo(ll2.Value, units);  
32.        }  
33.  
34.        // Overload for UK post codes  
35.        public static double? BetweenTwoUKPostCodes(string postcodeA, string postcodeB)  
36.        {  
37.            return BetweenTwoPostCodes(postcodeA, postcodeB, "GB", Units.Miles);  
38.        }  
39.  
40.        // Uses the Google API to resolve a post code (within the specified country)  
41.        public static Coords? PostCodeToLongLat(string postcode, string countryCodeWithin)  
42.        {  
43.            // Download the XML response from Google  
44.            var client = new WebClient();  
45.            var encodedPostCode = HttpUtility.UrlEncode(postcode);  
46.            var url = string.Format("http://maps.google.com/maps/geo?q={0}&output=xml", encodedPostCode);  
47.            var xml = client.DownloadString(url);  
48.            var doc = new XmlDocument();  
49.            doc.LoadXml(xml);  
50.  
51.            // Create a custom namespace manager  
52.            var nsmgr = new XmlNamespaceManager(doc.NameTable);  
53.            nsmgr.AddNamespace("ge", "http://earth.google.com/kml/2.0");  
54.            nsmgr.AddNamespace("oa", "urn:oasis:names:tc:ciq:xsdschema:xAL:2.0");  
55.  
56.            // Any results?  
57.            var nodelist = doc.SelectNodes("//ge:kml/ge:Response/ge:Placemark", nsmgr);  
58.            if (nodelist == null || nodelist.Count == 0) return null;  
59.  
60.            // Results are already ordered by accuracy, so take the first one  
61.            var node = nodelist[0];  
62.  
63.            // Check the Country constraint  
64.            var countryname = node.SelectSingleNode("oa:AddressDetails/oa:Country/oa:CountryNameCode", nsmgr);  
65.            if (countryname.FirstChild.Value != countryCodeWithin)  
66.                return null;  
67.  
68.            // Get the raw Long/Lat coordinates (I wish there was a nicer way..  
69.            // perhaps averaging the LongLat enclosing box?)  
70.            var coords = node.SelectSingleNode("ge:Point/ge:coordinates", nsmgr).FirstChild.Value.Split(',');  
71.            double longitude;  
72.            double lattitude;  
73.            if (!Double.TryParse(coords[0], out longitude)) return null;  
74.            if (!Double.TryParse(coords[1], out lattitude)) return null;  
75.  
76.            return new Coords  
77.                       {  
78.                           Longitude = longitude,  
79.                           Latitude = lattitude  
80.                       };  
81.        }  
82.  
83.        public static double DistanceTo(this Coords from, Coords to, Units units)  
84.        {  
85.            // Haversine Formula...  
86.            var dLat1InRad = from.Latitude * (Math.PI / 180.0);  
87.            var dLong1InRad = from.Longitude * (Math.PI / 180.0);  
88.            var dLat2InRad = to.Latitude * (Math.PI / 180.0);  
89.            var dLong2InRad = to.Longitude * (Math.PI / 180.0);  
90.  
91.            var dLongitude = dLong2InRad - dLong1InRad;  
92.            var dLatitude = dLat2InRad - dLat1InRad;  
93.  
94.            // Intermediate result a.  
95.            var a = Math.Pow(Math.Sin(dLatitude / 2.0), 2.0) +  
96.                    Math.Cos(dLat1InRad) * Math.Cos(dLat2InRad) *  
97.                    Math.Pow(Math.Sin(dLongitude / 2.0), 2.0);  
98.  
99.            // Intermediate result c (great circle distance in Radians).  
100.            var c = 2.0 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1.0 - a));  
101.  
102.            // Unit of measurement  
103.            var radius = 6371;  
104.            if (units == Units.Miles) radius = 3959;  
105.  
106.            return radius * c;  
107.        }  
108.    }  
109.}  
/xml>