Attaching a viewpoint to a mobile object (ctnd)

Question

I am trying to attach the user's viewpoint to a moving object in Java 3D. I failed until now to have my code working.
Here is a piece of code that exhibits the problem. I used the HelloWorld3D that is in the Java 3D examples from Sun. I inserted an attachViewpoint() method where the vpTransform.addChild(path) line throws an exception: only a BranchGroup may be added. If this line is commented out, the program compiles and runs but I doesn't track the object.
Do you have an idea to have this code working?
Many thanks
Pierre
* @(#)HelloJava3Db.java 1.1 00/09/22 13:48
* Copyright (c) 1996-2000 Sun Microsystems, Inc. All Rights Reserved.
* Sun grants you ("Licensee") a non-exclusive, royalty free, license to use,
* modify and redistribute this software in source and binary code form,
* provided that i) this copyright notice and license appear on all copies of
* the software; and ii) Licensee does not utilize the software in a manner
* which is disparaging to Sun.
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
* IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
* NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
* LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING
* OR DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS
* LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
* INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
* CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
* OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGES.
* This software is not designed or intended for use in on-line control of
* aircraft, air traffic, aircraft navigation or aircraft communications; or in
* the design, construction, operation or maintenance of any nuclear
* facility. Licensee represents and warrants that it will not use or
* redistribute the Software for such purposes.
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Frame;
import java.awt.event.*;
import java.awt.GraphicsConfiguration;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.ColorCube;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;
// HelloJava3De attempts to track a translating cube
public class HelloJava3De extends Applet {
public SimpleUniverse simpleU;
public BranchGroup createSceneGraph() {
// Create the root of the branch graph
BranchGroup objRoot = new BranchGroup();
Transform3D translate = new Transform3D();
TransformGroup objTranslate = new TransformGroup();
objTranslate.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
objRoot.addChild(objTranslate);
objTranslate.addChild(new ColorCube(0.4));
Alpha translationAlpha = new Alpha(-1, 4000);
Transform3D translationAxis = new Transform3D();
translationAxis.rotY(-Math.PI/2.0d);
PositionInterpolator path = new PositionInterpolator(translationAlpha, objTranslate, translationAxis, 0.0f, -10.0f);
BoundingSphere bounds = new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 100.0);
path.setSchedulingBounds(bounds);
objTranslate.addChild(path);
// Let Java 3D perform optimizations on this scene graph.
objRoot.compile();
return objRoot;
} // end of CreateSceneGraph method of HelloJava3De
public boolean attachViewpoint() {
Vector3f initialViewpoint = new Vector3f(0.0f, 0.0f, 6.0f);
Transform3D translate = new Transform3D();
translate.setTranslation(initialViewpoint);
TransformGroup vpTransform = null;
vpTransform = simpleU.getViewingPlatform().getViewPlatformTransform();
vpTransform.setTransform(translate);
Alpha translationAlpha = new Alpha(-1, 4000);
Transform3D translationAxis = new Transform3D();
translationAxis.rotY(-Math.PI/2.0d);
PositionInterpolator path = new PositionInterpolator(translationAlpha, vpTransform, translationAxis, 0.0f, -10.0f);
BoundingSphere bounds = new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 100.0);
path.setSchedulingBounds(bounds);
vpTransform.addChild(path);
return true;
// Create a simple scene and attach it to the virtual universe
public HelloJava3De() {
setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
Canvas3D canvas3D = new Canvas3D(config);
add("Center", canvas3D);
BranchGroup scene = createSceneGraph();
// SimpleUniverse is a Convenience Utility class
simpleU = new SimpleUniverse(canvas3D);
simpleU.addBranchGraph(scene);
attachViewpoint();
} // end of HelloJava3De (constructor)
// The following allows this to be run as an application
// as well as an applet
public static void main(String[] args) {
Frame frame = new MainFrame(new HelloJava3De(), 256, 256);
} // end of main (method of HelloJava3De)
} // end of class HelloJava3De

Answer 1

I finally found a way to attach a viewpoint to a moving object. I could not do it with the SimpleUniverse pre-defined class and I had to create a VirtualUniverse. May be, there is a workaround that I am not aware of...
There are some other posts asking for this type of program and here is my code. I hope this will help.
Pierre
* @(#)HelloJava3Db.java 1.1 00/09/22 13:48
* Copyright (c) 1996-2000 Sun Microsystems, Inc. All Rights Reserved.
* Sun grants you ("Licensee") a non-exclusive, royalty free, license to use,
* modify and redistribute this software in source and binary code form,
* provided that i) this copyright notice and license appear on all copies of
* the software; and ii) Licensee does not utilize the software in a manner
* which is disparaging to Sun.
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
* IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
* NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
* LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING
* OR DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS
* LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
* INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
* CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
* OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGES.
* This software is not designed or intended for use in on-line control of
* aircraft, air traffic, aircraft navigation or aircraft communications; or in
* the design, construction, operation or maintenance of any nuclear
* facility. Licensee represents and warrants that it will not use or
* redistribute the Software for such purposes.
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Frame;
import java.awt.event.*;
import java.awt.GraphicsConfiguration;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.ColorCube;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;
// HelloJava3De tracks a translating cube
public class HelloJava3De extends Applet {
public VirtualUniverse virtualU;
public Alpha translationAlpha;
public BranchGroup createSceneGraph() {
     // Create the root of the branch graph
     BranchGroup objRoot = new BranchGroup();
     Transform3D translate = new Transform3D();
     TransformGroup objTranslate = new TransformGroup();
     objTranslate.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
     objRoot.addChild(objTranslate);
     objTranslate.addChild(new ColorCube(0.4));
     Transform3D translationAxis = new Transform3D();
     translationAxis.rotY(-Math.PI/2.0d);
     PositionInterpolator path = new PositionInterpolator(translationAlpha, objTranslate, translationAxis, 0.0f, -10.0f);
     BoundingSphere bounds = new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 100.0);
     path.setSchedulingBounds(bounds);
     objTranslate.addChild(path);
     // Let Java 3D perform optimizations on this scene graph.
     objRoot.compile();
     return objRoot;
} // end of CreateSceneGraph method of HelloJava3De
public BranchGroup createViewpoint(Canvas3D canvas3D) {
     // Create the view, platform, and environment.
     //Should roughly correspond to a SimpleUniverse
     View myView = new View();
     ViewPlatform myViewPlatform = new ViewPlatform();
     TransformGroup viewGroup = new TransformGroup();
     myView.addCanvas3D(canvas3D);
     myView.setPhysicalBody(new PhysicalBody());
     myView.setPhysicalEnvironment(new PhysicalEnvironment());
     viewGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
     //viewGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
     //viewGroup.setCapability(TransformGroup.ALLOW_CHILDREN_EXTEND);
     viewGroup.addChild(myViewPlatform);
     myView.attachViewPlatform(myViewPlatform);
     BranchGroup bgView = new BranchGroup();
     bgView.addChild(viewGroup);
     // Create the interpolator
     Transform3D translationAxis = new Transform3D();
     translationAxis.rotY(-Math.PI/2.0d);
     PositionInterpolator path = new PositionInterpolator(translationAlpha, viewGroup, translationAxis, 2.0f, -8.0f);
     BoundingSphere bounds = new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 100.0);
     path.setSchedulingBounds(bounds);
     viewGroup.addChild(path);
     return bgView;
// Create a simple scene and attach it to the virtual universe
public HelloJava3De() {
setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
Canvas3D canvas3D = new Canvas3D(config);
add("Center", canvas3D);
     // Create the virtual universe
virtualU = new VirtualUniverse();
     Locale myLocale = new Locale(virtualU);
     // Create the Alpha object
     translationAlpha = new Alpha(-1, 4000);
BranchGroup scene = createSceneGraph();
     BranchGroup view = createViewpoint(canvas3D);
myLocale.addBranchGraph(scene);     
     myLocale.addBranchGraph(view);
} // end of HelloJava3De (constructor)
// The following allows this to be run as an application
// as well as an applet
public static void main(String[] args) {
     Frame frame = new MainFrame(new HelloJava3De(), 256, 256);
} // end of main (method of HelloJava3De)
} // end of class HelloJava3De