Hi
I am trying to get the perspective parameters from the
view matrix used to generate the scene on my canvas.
When I use Canvas.getVworldToImagePlate()
the last row of the matrix is
0 0 0 1
I've reading up on my projective geometry over the
last week, and for a perspective transformation,
the first three numbers in the last row SHOULD NOT be zero.
They will only be zero for a parallel projection.
Is this a bug in Java3D?
or is there another way to get the perspective parameters
(I'm trying to work out the co-ordinates of all points that
get displayed at a particular x,y pixel location).
I have attached an example program that will
print out the Virtual world to Image plate transform.
I'm using Windows NT and Java3D 1.2 Beta 2.
Any comments would be very gratefully accepted.
thanks
Robert
--
Robert McLaughlin
Medical Vision Lab
Department of Engineering Science
University of Oxford
/*
* @(#)HelloUniverse.java 1.48 00/02/10 13:14:09
*
* 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.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.*;
public class HelloUniverse extends Applet {
public BranchGroup createSceneGraph() {
// Create the root of the branch graph
BranchGroup objRoot = new BranchGroup();
// Create the transform group node and initialize it to the
// identity. Enable the TRANSFORM_WRITE capability so that
// our behavior code can modify it at runtime. Add it to the
// root of the subgraph.
TransformGroup objTrans = new TransformGroup();
objTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
objRoot.addChild(objTrans);
// Create a simple shape leaf node, add it to the scene graph.
objTrans.addChild(new ColorCube(0.4));
// Create a new Behavior object that will perform the desired
// operation on the specified transform object and add it into
// the scene graph.
Transform3D yAxis = new Transform3D();
Alpha rotationAlpha = new Alpha(-1, Alpha.INCREASING_ENABLE,
0, 0,
4000, 0, 0,
0, 0, 0);
RotationInterpolator rotator =
new RotationInterpolator(rotationAlpha, objTrans, yAxis,
0.0f, (float) Math.PI*2.0f);
BoundingSphere bounds =
new BoundingSphere(new Point3d(0.0,0.0,0.0), 100.0);
rotator.setSchedulingBounds(bounds);
objTrans.addChild(rotator);
// Have Java 3D perform optimizations on this scene graph.
objRoot.compile();
return objRoot;
}
public HelloUniverse() {
setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
Canvas3D c = new Canvas3D(config);
add("Center", c);
// Create a simple scene and attach it to the virtual universe
BranchGroup scene = createSceneGraph();
SimpleUniverse u = new SimpleUniverse(c);
// This will move the ViewPlatform back a bit so the
// objects in the scene can be viewed.
u.getViewingPlatform().setNominalViewingTransform();
u.addBranchGraph(scene);
// NEW CODE ADDED HERE BY RAM 25/4/2000
// to test Canvas.getVworldToImagePlate()
//
// Uncomment the following line if you want to use
// parallel projection instead of perspective projection.
//
// c.getView().setProjectionPolicy(View.PARALLEL_PROJECTION);
// Get the Virtual World to Image plate transform.
// Print it to the screen.
// For perspective, last row of matrix
// should NOT be 0.0, 0.0, 0.0, 1.0
//
Transform3D vWorldToImagePlate = new Transform3D();
c.getVworldToImagePlate(vWorldToImagePlate);
System.out.println("VWorld to ImagePlate transform:");
System.out.println(vWorldToImagePlate + "\n\n");
System.out.println("For perspective, last row of matrix should NOT be");
System.out.println("0.0, 0.0, 0.0, 1.0");
System.out.println("------------------------");
// END OF NEW CODE ADDED BY RAM 25/4/2000
}
//
// The following allows HelloUniverse to be run as an application
// as well as an applet
//
public static void main(String[] args) {
new MainFrame(new HelloUniverse(), 256, 256);
}
}
