Java 如何设置ViewingPlatform和更新TransformGroup？

我在TransformGroup中有一个场景，允许鼠标缩放/旋转/平移

我需要将摄影机位置设置回足够远的位置，以便可以看到整个场景，我使用以下代码执行此操作：

    // Position the position from which the user is viewing the scene
    ViewingPlatform viewPlatform = universe.getViewingPlatform();
    TransformGroup viewTransform = viewPlatform.getViewPlatformTransform();
    Transform3D t3d = new Transform3D();
    viewTransform.getTransform(t3d);
    t3d.lookAt(new Point3d(0,0,50), new Point3d(0,0,0), new Vector3d(0,1,0));
    t3d.invert();
    viewTransform.setTransform(t3d);

执行上述代码的工作原理是，我可以用鼠标操纵场景。但是，如果我换掉这一行：

t3d.lookAt(new Point3d(0,0,50), new Point3d(0,0,0), new Vector3d(0,1,0));

与：

我失去了用鼠标操纵屏幕的能力

我如何保持在将相机进一步向后推的同时使用鼠标进行变换的能力，以便查看整个屏幕

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非常感谢

.setActivationRadius使对象显示在范围内，但.setBackClipDistance有什么作用？后剪辑距离确定场景对象的后（后）距离保持可见的距离。

    GraphicsConfiguration config = SimpleUniverse.getPreferredConfiguration();
    Canvas3D canvas3d = new Canvas3D(config);

    // Manually create the viewing platform so that we can customize it
    ViewingPlatform viewingPlatform = new ViewingPlatform();

    // **** This is the part I was missing: Activation radius
    viewingPlatform.getViewPlatform().setActivationRadius(300f);

    // Set the view position back far enough so that we can see things
    TransformGroup viewTransform = viewingPlatform.getViewPlatformTransform();
    Transform3D t3d = new Transform3D();
    // Note: Now the large value works
    t3d.lookAt(new Point3d(0,0,150), new Point3d(0,0,0), new Vector3d(0,1,0));
    t3d.invert();
    viewTransform.setTransform(t3d);

    // Set back clip distance so things don't disappear 
    Viewer viewer = new Viewer(canvas3d);
    View view = viewer.getView();
    view.setBackClipDistance(300);

    SimpleUniverse universe = new SimpleUniverse(viewingPlatform, viewer);

    GraphicsConfiguration config = SimpleUniverse.getPreferredConfiguration();
    Canvas3D canvas3d = new Canvas3D(config);

    // Manually create the viewing platform so that we can customize it
    ViewingPlatform viewingPlatform = new ViewingPlatform();

    // **** This is the part I was missing: Activation radius
    viewingPlatform.getViewPlatform().setActivationRadius(300f);

    // Set the view position back far enough so that we can see things
    TransformGroup viewTransform = viewingPlatform.getViewPlatformTransform();
    Transform3D t3d = new Transform3D();
    // Note: Now the large value works
    t3d.lookAt(new Point3d(0,0,150), new Point3d(0,0,0), new Vector3d(0,1,0));
    t3d.invert();
    viewTransform.setTransform(t3d);

    // Set back clip distance so things don't disappear 
    Viewer viewer = new Viewer(canvas3d);
    View view = viewer.getView();
    view.setBackClipDistance(300);

    SimpleUniverse universe = new SimpleUniverse(viewingPlatform, viewer);