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();