Windows Phone 地圖定位 及匯出GPX檔案

1  概述

通過ArcGIS Runtime for WindowsPhone SDK開發手機地圖應用，能夠定位所在位置，並將多個定位位置資訊匯出為GPX檔案，供其他軟體，如ArcMap、Google Earth等調用。本文將介紹如何?地圖定位，以及匯出GPX檔案的功能。

2  GeoCoordinateWatcher

Windows Phone SDK提供了GeoCoordinateWatcher類實現定位相關功能，需要引入System.Device.dll庫，添加System.Device.Location命名空間。

2.1 參數設定

使用GeoCoordinateWatcher，需要建立一個執行個體，並設定定位精度、移動間距等基本屬性，另外監聽狀態變化、結果變化等事件。如下代碼所示：

if (_watcher == null){    _watcher = new GeoCoordinateWatcher(GeoPositionAccuracy.High); // 使用高定位精度                    _watcher.MovementThreshold = 50; // 最小移動間距，單位米，大於該間距的點才會觸發PositionChanged事件    _watcher.StatusChanged += new EventHandler<GeoPositionStatusChangedEventArgs>(watcher_StatusChanged);    _watcher.PositionChanged += new EventHandler<GeoPositionChangedEventArgs<GeoCoordinate>>(watcher_PositionChanged);}

2.2 啟動定位

啟動定位功能，即調用GeoCoordinateWatcher的Start方法，如下：

_watcher.Start();

2.3 定位狀態

監聽定位狀態變化事件，如果出錯可提示使用者，如下：

void watcher_StatusChanged(object sender, GeoPositionStatusChangedEventArgs e){    switch (e.Status)    {        case GeoPositionStatus.Disabled:                                if (_watcher.Permission == GeoPositionPermission.Denied)            {                            txtStatus.Text = "應用程式無權訪問定位服務";            }            else            {                txtStatus.Text = "裝置不支援定位服務";            }            break;        case GeoPositionStatus.Initializing:                                break;        case GeoPositionStatus.NoData:                                txtStatus.Text = "擷取定位元據失敗";             break;        case GeoPositionStatus.Ready:            txtStatus.Text = "GPS已經就緒";            break;    }}

2.4 定位結果

對定位結果的處理，需要在定位位置變化事件中進行，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錨點位置                _gLocation.Geometry = ptCurrent;                //更新軌跡線                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 記錄GPS定位資訊                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級比例尺                      }            catch (Exception ex)            {                MessageBox.Show("顯示定位資訊錯誤");            }}

其中ESRI.ArcGIS.Client.Projection.WebMercator是用於將GPS獲得的WGS 84經緯度座標轉換為Web Mercator投影座標，這需要根據座標系的具體情況來選擇，如果地圖座標系本身就是WGS84，則無需轉換，如果地圖是Web Mercator，則需要進行轉換，如果地圖是其他座標系，如Xian1980,或CGCS2000等，則需要調用ArcGIS
Server的Geometry Service進行線上轉換。

2.5 停止定位

當需要停止定位的時候，直接調用Stop方法即可，如下：

if (_watcher != null){    _watcher.Stop();   txtStatus.Text = "";   _gpsLayer.Graphics.Clear();}

3 匯出GPX檔案

在上文定位結果處理中，已經將每次位置記錄儲存為GpsInfo對象，便於進行統一的匯出處理。

3.1 GpsInfo

GpsInfo對象只是簡單的屬性欄位集合，用於記錄GPS裝置擷取的資料資訊。其屬性如下：

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則提供了將GpsInfo寫入GPX檔案的功能，代碼如下：

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))                    {                        //寫xml檔案開始<?xml version="1.0" encoding="utf-8" ?>                        xmlWriter.WriteStartDocument();                        //寫根節點                        xmlWriter.WriteStartElement("gpx", "http://www.topografix.com/GPX/1/0");                        //給節點添加屬性                        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");                        //寫內容根節點                        xmlWriter.WriteStartElement("trk");                        //寫內容根節點                        xmlWriter.WriteStartElement("trkseg");                        //寫GPS資訊節點                        foreach (GpsInfo gpsInfo in _lstGpsInfo)                        {                            xmlWriter.WriteStartElement("trkpt");                            //給節點添加屬性                            xmlWriter.WriteAttributeString("lat", gpsInfo.Latitude.ToString());                            xmlWriter.WriteAttributeString("lon", gpsInfo.Longitude.ToString());                            //添加子節點                            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();//清空記錄            }            catch (Exception ex)            {                System.Windows.MessageBox.Show("寫GPX檔案錯誤：" + ex.Message);            }        }    }

在調用的時候，只需要指定gpx檔案名稱，然後調用相關的方法，例如變數定義：

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);

匯出GPX檔案：

_gpxWriter.WriteToGpx();