怎样实现对vtkAssembly装配体里的单个物件单独操作？

怎样实现对vtkAssembly装配体里的单个物件单独操作，可以实现对其单独选定、移动、放大缩小等操作？
我参考了http://tieba.baidu.com/p/2618380891帖子里的方法，用vtk默认的
1.将输入法切换到英文
2.按“a”
3.按鼠标中键并移动
但是只能够对不同的actor操作，当单独的一个actor也正好是装配体Assembly里的一员时，单独操作那个actor时，装配体里相对应的那一员也会同时操作，比如下图中，红绿蓝组合在一起的是一个装配体，左上角那个绿椎体是单独的一个actor，对绿椎体单独操作时，装配体中相对应的绿锥体也在移动。
但我现在想的是直接对actor操作，有什么方法么。把代码贴出来，集思广益一下哈~

#include "vtkRenderWindowInteractor.h"
#include "vtkRenderer.h"
#include "vtkRenderWindow.h"
#include "vtkMarchingCubes.h"
#include "vtkStripper.h"
#include "vtkActor.h"
#include "vtkPolyDataMapper.h"
#include "vtkProperty.h"
#include "vtkCamera.h"
#include "vtkSmartPointer.h"
#include <vtkImageActor.h>
#include <vtkImageData.h>
#include <vtkSTLWriter.h>
#include "vtkTriangleFilter.h"
#include "vtkPolyDataNormals.h"
#include "vtkAssembly.h"
#include "vtkDecimatePro.h"
#include "vtkSmoothPolyDataFilter.h"
#include "vtkCubeSource.h"
#include "vtkCylinderSource.h"
#include "vtkSphereSource.h"
#include "vtkConeSource.h"
// vtkSphereSource* sphere;
// vtkConeSource *cone;
void main(){
vtkSphereSource* sphere= vtkSphereSource::New();
vtkPolyDataMapper* sphereMapper= vtkPolyDataMapper::New();
sphereMapper-> SetInputConnection(sphere-> GetOutputPort());
vtkActor* sphereActor= vtkActor::New();
sphereActor ->SetMapper( sphereMapper);
sphereActor-> SetOrigin (2, 1, 3);
sphereActor ->RotateY (96);
sphereActor ->SetPosition (2.25 ,0 ,0);
sphereActor ->GetProperty()->SetColor (1, 0, 1);
vtkCubeSource *cube= vtkCubeSource::New();
vtkPolyDataMapper* cubeMapper= vtkPolyDataMapper::New();
cubeMapper ->SetInputConnection(cube-> GetOutputPort());
vtkActor* cubeActor= vtkActor::New();
cubeActor-> SetMapper(cubeMapper);
cubeActor->SetPosition(0.0,.25,0);
cubeActor->GetProperty()->SetColor(0,0,1);
vtkConeSource *cone= vtkConeSource::New();
vtkPolyDataMapper* coneMapper= vtkPolyDataMapper::New();
coneMapper->SetInputConnection(cone-> GetOutputPort());//coneMapper-> SetResolveCoincidentTopologyToPolygonOffset();
vtkActor* coneActor= vtkActor::New();
coneActor->SetMapper(coneMapper);
coneActor->SetPosition(0,0,.25);
coneActor-> GetProperty()->SetColor(0,1,0);
//
vtkCylinderSource* cylinder= vtkCylinderSource::New();
vtkPolyDataMapper* cylinderMapper= vtkPolyDataMapper::New();
cylinderMapper->SetInputConnection(cylinder->GetOutputPort());
//cylinderMapper-> SetResolveCoincidentTopologyToPolygonOffset();
vtkActor* cylinderActor= vtkActor::New();
cylinderActor->SetMapper(cylinderMapper);cylinderActor->SetPosition(0,0,.25);
cylinderActor->GetProperty()->SetColor(1,0,0);
//ation in space.
vtkAssembly* assembly= vtkAssembly::New();
assembly->AddPart(cylinderActor);
assembly->AddPart(sphereActor);
assembly->AddPart(cubeActor);
assembly->AddPart(coneActor);
assembly->SetOrigin(5,10,15);
assembly->AddPosition (5, 0,0);
//assembly ->RotateX(15);
vtkRenderer* ren1= vtkRenderer::New();
//vtkRenderer* ren2= vtkRenderer::New();
vtkRenderWindow* renWin= vtkRenderWindow::New();
renWin->AddRenderer(ren1);
//renWin->AddRenderer(ren2);
vtkRenderWindowInteractor* iren= vtkRenderWindowInteractor::New();
iren->SetRenderWindow(renWin);
ren1-> AddActor(assembly);
ren1->AddActor(coneActor);
//ren2->AddActor(cubeActor);
ren1->SetBackground(0.1,0.2,.4);
renWin->SetSize(200,200);
//# Set up the camera to get a particular view of the scene
vtkCamera* camera= vtkCamera::New();
camera-> SetClippingRange (21.9464,30.0179);
camera ->SetFocalPoint(3.49221,2.28844,-0.970866);
camera->SetPosition (3.49221,2.28844,24.5216);
camera->SetViewAngle (30);
camera->SetViewUp(0,1,0);
ren1->SetActiveCamera(camera);
//iren AddObserver UserEvent {wm deiconify . vtkInteract}
renWin->Render();
iren->Start();
}