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May 16, 2019 13:33
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using System; | |
using System.Collections.Generic; | |
using System.Text; | |
using Xamarin.Forms.GoogleMaps; | |
namespace TrackingSample.Helpers | |
{ | |
public static class PolylineHelper | |
{ | |
/// <summary> | |
/// Decode google style polyline coordinates. | |
/// </summary> | |
/// <param name="encodedPoints"></param> | |
/// <returns></returns> | |
public static IEnumerable<Position> Decode(string encodedPoints) | |
{ | |
if (string.IsNullOrEmpty(encodedPoints)) | |
throw new ArgumentNullException("encodedPoints"); | |
char[] polylineChars = encodedPoints.ToCharArray(); | |
int index = 0; | |
int currentLat = 0; | |
int currentLng = 0; | |
int next5bits; | |
int sum; | |
int shifter; | |
while (index < polylineChars.Length) | |
{ | |
// calculate next latitude | |
sum = 0; | |
shifter = 0; | |
do | |
{ | |
next5bits = (int)polylineChars[index++] - 63; | |
sum |= (next5bits & 31) << shifter; | |
shifter += 5; | |
} while (next5bits >= 32 && index < polylineChars.Length); | |
if (index >= polylineChars.Length) | |
break; | |
currentLat += (sum & 1) == 1 ? ~(sum >> 1) : (sum >> 1); | |
//calculate next longitude | |
sum = 0; | |
shifter = 0; | |
do | |
{ | |
next5bits = (int)polylineChars[index++] - 63; | |
sum |= (next5bits & 31) << shifter; | |
shifter += 5; | |
} while (next5bits >= 32 && index < polylineChars.Length); | |
if (index >= polylineChars.Length && next5bits >= 32) | |
break; | |
currentLng += (sum & 1) == 1 ? ~(sum >> 1) : (sum >> 1); | |
yield return new Position(Convert.ToDouble(currentLat) / 1E5, Convert.ToDouble(currentLng) / 1E5); | |
} | |
} | |
/// <summary> | |
/// Encode it | |
/// </summary> | |
/// <param name="points"></param> | |
/// <returns></returns> | |
public static string Encode(IEnumerable<Position> points) | |
{ | |
var str = new StringBuilder(); | |
var encodeDiff = (Action<int>)(diff => | |
{ | |
int shifted = diff << 1; | |
if (diff < 0) | |
shifted = ~shifted; | |
int rem = shifted; | |
while (rem >= 0x20) | |
{ | |
str.Append((char)((0x20 | (rem & 0x1f)) + 63)); | |
rem >>= 5; | |
} | |
str.Append((char)(rem + 63)); | |
}); | |
int lastLat = 0; | |
int lastLng = 0; | |
foreach (var point in points) | |
{ | |
int lat = (int)Math.Round(point.Latitude * 1E5); | |
int lng = (int)Math.Round(point.Longitude * 1E5); | |
encodeDiff(lat - lastLat); | |
encodeDiff(lng - lastLng); | |
lastLat = lat; | |
lastLng = lng; | |
} | |
return str.ToString(); | |
} | |
} | |
} |
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