VTK: 相機參數控制

原創

2020-02-20 23:50

用戶是通過相機來觀察三位場景中的物體，精準控制相機來實現用戶從不同角度、不同位置來觀察三位物體。

我們可以通過GetActiveCamera()函數來獲取當前渲染器(vtkRenderer)中的默認相機。也可以通過SetActiveCamera()函數來設置一個新相機到渲染器中。函數簽名如下：

 // Description:
  // Specify the camera to use for this renderer.
  void SetActiveCamera(vtkCamera *);

  // Description:
  // Get the current camera. If there is not camera assigned to the
  // renderer already, a new one is created automatically.
  // This does *not* reset the camera.
  vtkCamera *GetActiveCamera();

相機的一些常規參數設置如下：

void vtkCamera::SetViewUp(double vx, double vy, double vz);% 朝上方向，默認爲(0, 1, 0)  
void vtkCamera::SetPosition(double x, double y, double z); % 相機位置，默認爲(0, 0, 1)  
void vtkCamera::SetFocalPoint(double x, double y, double z);% 焦點，默認爲(0, 0, 0)  
void vtkCamera::SetClippingRange(double dNear, double dFar);% 前後裁剪平面位置，默認爲(0.1, 1000)  
void vtkCamera::SetViewAngle(double angle); % 視角，默認爲30度

相機的運動控制，主要包括旋轉、縮放等一系列運動。旋轉主要包括相機圍繞焦點水平、垂直旋轉；焦點圍繞相機水平垂直旋轉；相機圍繞投影方向旋轉五大類。函數標籤如下：

// Description:
  // Rotate the camera about the direction of projection.  This will
  // spin the camera about its axis.
  void Roll(double angle); //圍繞投影方向自旋轉

  // Description:
  // Rotate the camera about the view up vector centered at the focal point.
  // Note that the view up vector is whatever was set via SetViewUp, and is
  // not necessarily perpendicular to the direction of projection.  The
  // result is a horizontal rotation of the camera.
  void Azimuth(double angle);//以焦點爲中心，水平旋轉相機

  // Description:
  // Rotate the focal point about the view up vector, using the camera's
  // position as the center of rotation. Note that the view up vector is
  // whatever was set via SetViewUp, and is not necessarily perpendicular
  // to the direction of projection.  The result is a horizontal rotation
  // of the scene.
  void Yaw(double angle);//以相機爲中心水平旋轉焦點

  // Description:
  // Rotate the camera about the cross product of the negative of the
  // direction of projection and the view up vector, using the focal point
  // as the center of rotation.  The result is a vertical rotation of the
  // scene.
  void Elevation(double angle);//以焦點爲中心垂直旋轉相機

  // Description:
  // Rotate the focal point about the cross product of the view up vector
  // and the direction of projection, using the camera's position as the
  // center of rotation.  The result is a vertical rotation of the camera.
  void Pitch(double angle); //以相機爲中心 垂直旋轉焦點

縮放主要是通過設置Dolly()或setDistance()完成。setDistance會移動焦點位置 Dolly是相機到焦點距離的一個除數

distance/Dolly

函數標籤如下：

 // Description:
  // Move the focal point so that it is the specified distance from
  // the camera position.  This distance must be positive.
  void SetDistance(double);

  // Description:
  // Divide the camera's distance from the focal point by the given
  // dolly value.  Use a value greater than one to dolly-in toward
  // the focal point, and use a value less than one to dolly-out away
  // from the focal point.
  void Dolly(double value);