Windows 8 地理位置定位 4.根据经纬度计算地面两点间的距离

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using Windows.Devices.Geolocation;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Core;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

namespace Win8Location
{
public sealed partial class DistanceAndSpeed : Page
{
Geolocator geo = null;
private double prevLongitude;
private double prevLatitude;
private double totalDistance;//(米)
private DateTimeOffset prevTime;
private TimeSpan totalTime = TimeSpan.Zero;

public DistanceAndSpeed()
{
this.InitializeComponent();
}

async private void btnStartTracking_Click(object sender, RoutedEventArgs e)
{
btnStartTracking.IsEnabled = false;
btnStopTracking.IsEnabled = true;
if (geo == null)
{
geo = new Geolocator();
}
if (geo != null)
{
geo.StatusChanged += geo_StatusChanged;
try
{
Geoposition position = await geo.GetGeopositionAsync();
string msg = position.Coordinate.Timestamp + ">开始定位并跟踪\n";
msg += "当前经度：" + position.Coordinate.Longitude + "\n";
msg += "当前纬度：" + position.Coordinate.Latitude + "\n\n";
txtMsg.Text += msg;
prevLongitude = position.Coordinate.Longitude;
prevLatitude = position.Coordinate.Latitude;
prevTime = position.Coordinate.Timestamp;
}
catch (Exception ex)
{
txtMsg.Text += DateTime.Now + ">出错了：" + ex.Message + "\n\n";
}
geo.PositionChanged += geo_PositionChanged;
}
}

async void geo_PositionChanged(Geolocator sender, PositionChangedEventArgs args)
{
Geoposition pos = args.Position;
double currLong = pos.Coordinate.Longitude;
double currLat = pos.Coordinate.Latitude;
DateTimeOffset currTime = pos.Coordinate.Timestamp;

double updateDistance = GetDistance(prevLongitude, prevLatitude, currLong, currLat);
totalDistance += updateDistance;
TimeSpan updateTime = currTime - prevTime;
totalTime += updateTime;

StringBuilder msg = new StringBuilder();
msg.Append(currTime + "\n");
msg.Append("当前经度：" + args.Position.Coordinate.Longitude + "\n");
msg.Append("当前纬度：" + args.Position.Coordinate.Latitude + "\n");
msg.Append("距上一个位置的距离（米）：" + updateDistance.ToString("0") + "\n");
msg.Append("距上一个位置经历的时间：" + updateTime.ToString(@"hh\:mm\:ss") + "\n");
msg.Append("距上一个位置间的平均速度（米/秒）：" + GetSpeed(updateDistance, updateTime).ToString("0") + "\n");
msg.Append("已经历的总路程（米）：" + totalDistance.ToString("0") + "\n");
msg.Append("已经历的总时间：" + totalTime.ToString(@"hh\:mm\:ss") + "\n");
msg.Append("已经历的总平均速度（米/秒）：" + GetSpeed(totalDistance, totalTime).ToString("0") + "\n\n");

await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
txtMsg.Text += msg;
});

prevLongitude = currLong;
prevLatitude = currLat;
prevTime = currTime;
}

async void geo_StatusChanged(Geolocator sender, StatusChangedEventArgs args)
{
string msg = DateTime.Now + ">定位器状态：" + args.Status + "\n\n";
await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
txtMsg.Text += msg;
});
}

private void btnStopTracking_Click(object sender, RoutedEventArgs e)
{
btnStartTracking.IsEnabled = true;
btnStopTracking.IsEnabled = false;
if (geo != null)
{
txtMsg.Text += DateTime.Now + ">停止位置跟踪\n\n";
geo.StatusChanged -= geo_StatusChanged;
geo.PositionChanged -= geo_PositionChanged;
}
}

/// <summary>
/// 根据经纬度计算地面两点间的距离
/// </summary>
/// <param name="prevLong">前一个点的经度</param>
/// <param name="prevLat">前一个点的纬度</param>
/// <param name="currLong">当前点的经度</param>
/// <param name="currLat">当前点的纬度</param>
/// <returns>两点间的距离(米)</returns>
private double GetDistance(double prevLong, double prevLat, double currLong, double currLat)
{
const double degreesToRadians = (Math.PI / 180.0);
const double earthRadius = 6371; // 地球半径平均值为6371千米

var prevRadLong = prevLong * degreesToRadians;
var prevRadLat = prevLat * degreesToRadians;
var currRadLong = currLong * degreesToRadians;
var currRadLat = currLat * degreesToRadians;

double cosX = Math.Cos(prevRadLat) * Math.Cos(currRadLat) * Math.Cos(prevRadLong - currRadLong) + Math.Sin(prevRadLat) * Math.Sin(currRadLat);
double X = Math.Acos(cosX);//两点与球心连线的夹角
double d = earthRadius * X * 1000;//单位转换为米
return d;
}

private double GetSpeed(double distance, TimeSpan timeSpan)
{
double speed = distance / timeSpan.TotalSeconds;
return speed;
}

private void btnClear_Click(object sender, RoutedEventArgs e)
{
txtMsg.Text = string.Empty;
}
}
}