Windows Phone 地图定位 及导出GPX文件

1  概述

通过ArcGIS Runtime for WindowsPhone SDK开发手机地图应用，能够定位所在位置，并将多个定位位置信息导出为GPX文件，供其他软件，如ArcMap、Google Earth等调用。本文将介绍如何实现地图定位，以及导出GPX文件的功能。

2  GeoCoordinateWatcher

Windows Phone SDK提供了GeoCoordinateWatcher类实现定位相关功能，需要引入System.Device.dll库，添加System.Device.Location命名空间。

2.1 参数设置

使用GeoCoordinateWatcher，需要创建一个实例，并设置定位精度、移动间距等基本属性，另外监听状态变化、结果变化等事件。如下代码所示：

if (_watcher == null)
{
_watcher = new GeoCoordinateWatcher(GeoPositionAccuracy.High); // 使用高定位精度
_watcher.MovementThreshold = 50; // 最小移动间距，单位米，大于该间距的点才会触发PositionChanged事件
_watcher.StatusChanged += new EventHandler<GeoPositionStatusChangedEventArgs>(watcher_StatusChanged);
_watcher.PositionChanged += new EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>(watcher_PositionChanged);
}

2.2 启动定位

启动定位功能，即调用GeoCoordinateWatcher的Start方法，如下：

_watcher.Start();

2.3 定位状态

监听定位状态变化事件，如果出错可提示用户，如下：

void watcher_StatusChanged(object sender, GeoPositionStatusChangedEventArgs e)
{
switch (e.Status)
{
case GeoPositionStatus.Disabled:
if (_watcher.Permission == GeoPositionPermission.Denied)
{
txtStatus.Text = "应用程序无权访问定位服务";
}
else
{
txtStatus.Text = "设备不支持定位服务";
}
break;
case GeoPositionStatus.Initializing:
break;
case GeoPositionStatus.NoData:
txtStatus.Text = "获取定位数据失败";
break;
case GeoPositionStatus.Ready:
txtStatus.Text = "GPS已经就绪";
break;
}
}

2.4 定位结果

对定位结果的处理，需要在定位位置变化事件中进行，如下所示：

void watcher_PositionChanged(object sender, GeoPositionChangedEventArgs<GeoCoordinate> e)
{
try
{
txtStatus.Text = "";

MapPoint point = new MapPoint(e.Position.Location.Longitude, e.Position.Location.Latitude);
ESRI.ArcGIS.Client.Projection.WebMercator mercator = new ESRI.ArcGIS.Client.Projection.WebMercator();
MapPoint ptCurrent = mercator.FromGeographic(point) as MapPoint;

//更新GPS定位点位置
_gLocation.Geometry = ptCurrent;

//更新轨迹线
if (_gpsPoints == null)
{
_gpsPoints = new PointCollection();
_gpsPoints.Add(ptCurrent);
}
else
{
_gpsPoints.Add(ptCurrent);
Polyline line = new Polyline();
line.Paths.Add(_gpsPoints);
_gTrackLine.Geometry = line;
}

#region 记录GPS定位信息

GpsInfo gpsInfo = new GpsInfo();
gpsInfo.Altitude = e.Position.Location.Altitude;
gpsInfo.Course = e.Position.Location.Course;
gpsInfo.HorizontalAccuracy = e.Position.Location.HorizontalAccuracy;
gpsInfo.Latitude = e.Position.Location.Latitude;
gpsInfo.Longitude = e.Position.Location.Longitude;
gpsInfo.Speed = e.Position.Location.Speed;
gpsInfo.VerticalAccuracy = e.Position.Location.VerticalAccuracy;
gpsInfo.Time = e.Position.Timestamp.DateTime;

_gpxWriter.AddGpsInfo(gpsInfo);

#endregion

_gpsLayer.Refresh();
map.ZoomToResolution(2.38865713397468, ptCurrent);//定位到16级比例尺
}
catch (Exception ex)
{
MessageBox.Show("显示定位信息错误");
}
}

其中ESRI.ArcGIS.Client.Projection.WebMercator是用于将GPS获得的WGS 84经纬度坐标转换为Web Mercator投影坐标，这需要根据坐标系的具体情况来选择，如果地图坐标系本身就是WGS84，则无需转换，如果地图是Web Mercator，则需要进行转换，如果地图是其他坐标系，如Xian1980,或CGCS2000等，则需要调用ArcGIS
Server的Geometry Service进行在线转换。

2.5 停止定位

当需要停止定位的时候，直接调用Stop方法即可，如下：

if (_watcher != null)
{
_watcher.Stop();

txtStatus.Text = "";
_gpsLayer.Graphics.Clear();
}

3 导出GPX文件

在上文定位结果处理中，已经将每次位置记录存储为GpsInfo对象，便于进行统一的导出处理。

3.1 GpsInfo

GpsInfo对象只是简单的属性字段集合，用于记录GPS设备获取的数据信息。其属性如下：

public class GpsInfo
{
private double _longitude = 0;
public double Longitude
{
get { return _longitude; }
set { _longitude = value; }
}

private double _latitude = 0;
public double Latitude
{
get { return _latitude; }
set { _latitude = value; }
}

private double _altitude = 0;
public double Altitude
{
get { return _altitude; }
set { _altitude = value; }
}

private double _speed = 0;
public double Speed
{
get { return _speed; }
set { _speed = value; }
}

private double _course = 0;
public double Course
{
get { return _course; }
set { _course = value; }
}

private double _horizontalAccuracy = 0;
public double HorizontalAccuracy
{
get { return _horizontalAccuracy; }
set { _horizontalAccuracy = value; }
}

private double _verticalAccuracy = 0;
public double VerticalAccuracy
{
get { return _verticalAccuracy; }
set { _verticalAccuracy = value; }
}

private DateTime _time = new DateTime();
public DateTime Time
{
get { return _time; }
set { _time = value; }
}
}

3.2 GpxWriter

GpxWriter则提供了将GpsInfo写入GPX文件的功能，代码如下：

public class GpxWriter
{
private string _gpxFile = "";
private IList<GpsInfo> _lstGpsInfo = null;

private XmlWriterSettings _settings = null;

public GpxWriter(string gpxFile)
{
_settings = new XmlWriterSettings();
_settings.Indent = true;
_settings.Encoding = new UTF8Encoding(false);
_settings.NewLineChars = Environment.NewLine;

_lstGpsInfo = new List<GpsInfo>();

_gpxFile = gpxFile;
}

public void AddGpsInfo(GpsInfo gpsInfo)
{
_lstGpsInfo.Add(gpsInfo);
}

public void WriteToGpx()
{
try
{
if (_lstGpsInfo == null || _lstGpsInfo.Count == 0) return;

IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication();
if (myIsolatedStorage.FileExists(_gpxFile) == true)
{
myIsolatedStorage.DeleteFile(_gpxFile);
}

using (IsolatedStorageFileStream stream = myIsolatedStorage.OpenFile(_gpxFile, FileMode.CreateNew))
{
using (XmlWriter xmlWriter = XmlWriter.Create(stream, _settings))
{
//写xml文件开始<?xml version="1.0" encoding="utf-8" ?>
xmlWriter.WriteStartDocument();

//写根节点
xmlWriter.WriteStartElement("gpx", "http://www.topografix.com/GPX/1/0");
//给节点添加属性
xmlWriter.WriteAttributeString("xmlns", "xsi", null, "http://www.w3.org/2001/XMLSchema-instance");
xmlWriter.WriteAttributeString("xmlns", "mbx", null, "http://www.motionbased.net/mbx");
xmlWriter.WriteAttributeString("xsi", "schemaLocation", null, "http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd http://www.motionbased.net/mbx http://www.motionbased.net/site/schemas/mbx/0.0.1/mbx.xsd"); xmlWriter.WriteAttributeString("creator", "YELLOW EAST http://weibo.com/yelloweast"); xmlWriter.WriteAttributeString("version", "1.0");

//写内容根节点
xmlWriter.WriteStartElement("trk");
//写内容根节点
xmlWriter.WriteStartElement("trkseg");

//写GPS信息节点
foreach (GpsInfo gpsInfo in _lstGpsInfo)
{
xmlWriter.WriteStartElement("trkpt");

//给节点添加属性
xmlWriter.WriteAttributeString("lat", gpsInfo.Latitude.ToString());
xmlWriter.WriteAttributeString("lon", gpsInfo.Longitude.ToString());

//添加子节点
xmlWriter.WriteElementString("ele", gpsInfo.Altitude.ToString());
xmlWriter.WriteElementString("time", gpsInfo.Time.ToShortDateString() + " " + gpsInfo.Time.ToLongTimeString());
xmlWriter.WriteElementString("course", gpsInfo.Course.ToString());
xmlWriter.WriteElementString("speed", gpsInfo.Speed.ToString());

xmlWriter.WriteEndElement();//trkpt
}

xmlWriter.WriteEndElement();//trkseg
xmlWriter.WriteEndElement();//trk
xmlWriter.WriteEndElement();//gpx

xmlWriter.WriteEndDocument();
}
}

_lstGpsInfo.Clear();//清空历史记录
}
catch (Exception ex)
{
System.Windows.MessageBox.Show("写GPX文件错误：" + ex.Message);
}
}
}

在调用的时候，只需要指定gpx文件名，然后调用相关的方法，例如变量定义：

private GpxWriter _gpxWriter = null;

初始化：

DateTime now = DateTime.Now;
string gpxName = String.Format("{0}-{1}-{2}_{3}-{4}-{5}.gpx", now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second);
_gpxWriter = new GpxWriter(gpxName);

导出GPX文件：

_gpxWriter.WriteToGpx();