WorldWind学习总结【三】定位功能分析

       定位功能分析，在PlaceFinder类里面

private void buttonGo_Click(object sender, System.EventArgs e)
{
   try
   {
    double lat = double.Parse(this.textBoxLatitude.Text);
    double lon = double.Parse(this.textBoxLongitude.Text);
    double alt = (double)this.numericUpDownAltitude.Value;
    m_WorldWindow.GotoLatLonAltitude(lat, lon, alt);
    }
      catch{}
}

       调用了 m_WorldWindow.GotoLatLonAltitude(lat, lon, alt); 在WorldWindow类里面的GotoLatLonAltitude函数如下：

public void GotoLatLonAltitude(double latitude, double longitude, double altitude)
        {
            this.drawArgs.WorldCamera.SetPosition(latitude, longitude,
                this.drawArgs.WorldCamera.Heading.Degrees,
                altitude,
                this.drawArgs.WorldCamera.Tilt.Degrees);
        }

        是WorldWindow对象的drawArgs属性的WorldCamera对象来控制的。而WorldCamera类继承自CameraBase类。在CameraBase类中才是具体的实现功能的代码：

        ///<summary>
        /// Sets camera position.
        ///</summary>
        ///<param name="lat">Latitude in decimal degrees</param>
        ///<param name="lon">Longitude in decimal degrees</param>
        ///<param name="heading">Heading in decimal degrees</param>
        ///<param name="_altitude">Altitude above ground level in meters</param>
        ///<param name="tilt">Tilt in decimal degrees</param>
        ///<param name="bank">Camera bank (roll) in decimal degrees</param>
        public virtual void SetPosition(double lat, double lon, double heading, double _altitude, double tilt, double bank)
        {
            if (double.IsNaN(lat)) lat = this._latitude.Degrees;
            if (double.IsNaN(lon)) lon = this._longitude.Degrees;
            if (double.IsNaN(heading)) heading = this._heading.Degrees;
            if (double.IsNaN(bank)) bank = this._bank.Degrees;

            m_Orientation = Quaternion4d.EulerToQuaternion(
                MathEngine.DegreesToRadians(lon),
                MathEngine.DegreesToRadians(lat),
                MathEngine.DegreesToRadians(heading));

            Point3d p = Quaternion4d.QuaternionToEuler(m_Orientation);

            _latitude.Radians = p.Y;//位置参数，私有变量赋值
            _longitude.Radians = p.X;
            _heading.Radians = p.Z;

            if (!double.IsNaN(tilt))
                Tilt = Angle.FromDegrees(tilt);
            if (!double.IsNaN(_altitude))
                this.Altitude = _altitude;
            this.Bank = Angle.FromDegrees(bank);
        }

        在上面这个函数里面进行了空值判断后，就开始给私有变量赋值，如经纬度等。但是到此并没有具体的"飞行"操作！查看CameraBase类的代码。发现有Update函数如下：

public virtual void Update(Device device)
        {
            viewPort = device.Viewport;

            Point3d p = Quaternion4d.QuaternionToEuler(m_Orientation);

            if(!double.IsNaN(p.Y))
                this._latitude.Radians = p.Y;
            if(!double.IsNaN(p.X))
                this._longitude.Radians = p.X;
            if(!double.IsNaN(p.Z))
                this._heading.Radians = p.Z;

            ComputeProjectionMatrix(viewPort);
            ComputeViewMatrix();
            device.Transform.Projection = m_ProjectionMatrix;
            device.Transform.View = m_ViewMatrix;
            device.Transform.World = m_WorldMatrix;
    
            ViewFrustum.Update(
                Matrix.Multiply(m_absoluteWorldMatrix,
                Matrix.Multiply(m_absoluteViewMatrix, m_absoluteProjectionMatrix)));

            // Old view range (used in quadtile logic)
            double factor = (this._altitude) / this._worldRadius;
            if(factor > 1)
                viewRange = Angle.FromRadians(Math.PI);
            else
                viewRange = Angle.FromRadians(Math.Abs(Math.Asin((this._altitude) / this._worldRadius))*2);

            // True view range 
            if(factor < 1)
                trueViewRange = Angle.FromRadians(Math.Abs(Math.Asin((this._distance) / this._worldRadius))*2);
            else
                trueViewRange = Angle.FromRadians(Math.PI);    
    
            World.Settings.cameraAltitudeMeters = Altitude;
            World.Settings.cameraLatitude = _latitude;
            World.Settings.cameraLongitude = _longitude;
            World.Settings.cameraHeading = _heading;
            World.Settings.cameraTilt = _tilt;
        }

         在里面可以看到ComputeProjectionMatrix(viewPort);  和ComputeViewMatrix();计算了投影变换和视图变换等。 在这2个函数里用了改变后的位置参数（经纬度，高度等）。然后再看一下Update函数在什么地方被调用：WoldWindow类的Render函数中被调用。再看一下Render函数：

         1， protected override void OnPaint(PaintEventArgs e)

         2，public void OnApplicationIdle(object sender, EventArgs e) 

         第一个就不用说了，窗体重绘函数。第二个是防止程序过度休眠的消息响应函数里。在程序启动时，就绑定了：

           Application.ThreadException += new ThreadExceptionEventHandler(Application_ThreadException);               

           MainApplication app = new MainApplication();

          好了，绕了一大圈，总结一下：

          1，CameraBase类是管理与虚拟相机位置相关信息的类，里面既包括如下：

          a，经纬度，高度，视角，角度，倾斜度等等位置/视角变量。

          b，各种变化矩阵和计算矩阵的函数，计算的参数由a中变量提供

          c，漫游相关的函数，包括平移，放大，缩小，移位（PointGoto）等功能，所做的操作也是依据用户操作修改a中的变量

          d，刷新/重置的函数

          e，其他

          当需要改变位置时，调用的是WorldWindow对象的drawArgs的WorldCamera函数，传入参数即可。在程序窗体Paint函数刷新界面时会自动进行视角变换及相关必须的计算。