坐标系统java3d

Question

根据此代码，stl文件的内容例如月亮形状的图像将不在框架的中心，并且其大小太大。如何将内容移动到框架的中心并减小其大小？感谢您的关注。

   public class HelloUniverse2 extends JFrame implements WindowListener, MouseWheelListener 
{


BranchGroup groupe; 
BranchGroup objRoot; 
Canvas3D canvas; 
TransformGroup tg ; 

public HelloUniverse2(String frameName) 
{ 
    super(frameName); 
    this.addWindowListener(this); 
    setLayout(new BorderLayout()); 

    canvas = new Canvas3D(SimpleUniverse.getPreferredConfiguration()); 
    add(canvas); 

    try{ 
        File file = new File("Moon.stl"); 
        final STLFileReader reader = new STLFileReader(file); 
        Scene scene = STLLoader.createScene(reader); 
        groupe = scene.getSceneGroup(); 
    }catch (IOException ex){ 
        System.out.println(ex); 
    } 
SimpleUniverse simpleU = new SimpleUniverse(canvas); 
canvas.addMouseWheelListener(this); 


simpleU.getViewingPlatform().setNominalViewingTransform(); 
objRoot =new BranchGroup();         
tg = new TransformGroup(); 
tg.addChild(groupe); 
objRoot.addChild(tg);         
tg.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE); 
tg.setCapability(TransformGroup.ALLOW_TRANSFORM_READ); 


MouseZoom myMouseZoom = new MouseZoom(); 
myMouseZoom.setTransformGroup(tg);  
myMouseZoom.setSchedulingBounds(new BoundingSphere()); 

MouseRotate rotate = new MouseRotate(tg); 
rotate.setSchedulingBounds(new BoundingSphere()); 

MouseTranslate translate = new MouseTranslate(tg); 
translate.setSchedulingBounds(new BoundingSphere()); 

objRoot.addChild(myMouseZoom); 
objRoot.addChild(rotate); 
objRoot.addChild(translate); 
simpleU.addBranchGraph(objRoot); 
View view = simpleU.getViewer().getView(); 
view.setBackClipDistance(1000);

    canvas.repaint(); 
}