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();