vtk中图元拾取类Picker分析

类的继承结构如下：

class VTKRENDERINGCORE_EXPORT vtkAbstractPicker : public vtkObject

class VTKRENDERINGCORE_EXPORT vtkAbstractPropPicker : public vtkAbstractPicker

class VTKRENDERINGCORE_EXPORT vtkPicker : public vtkAbstractPropPicker

class VTKINTERACTIONWIDGETS_EXPORT vtkResliceCursorPicker : public vtkPicker//交互部分自定义的一个类