Attached below is a utility class which will transform VWorld points from a
local coordinate system to pixel coordinates. It takes into account the local
to VWorld transform as well as the view projection type (perspective vs
parallel).
Doug Gehringer
Sun Microsystems
> Date: Mon, 29 Mar 1999 20:45:19 +0100 (BST)
> From: Jon Beniston <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> cc: kcr@eng
> Subject: [java3d] VWorld to Pixel Coordinates
> MIME-Version: 1.0
>
> Hi,
>
> In an e-mail some time ago (below) you gave a formula that supposedly
> converts between image plate and pixel coordinates. I've tried to use
> this to convert from VWorld to pixel coordinates:
>
> // Convert p from VWorld to image plate coordinates
> Point3d p = new Point3d(10.0, 10.0, 10.0);
> Tranform3D t = new Transform3D();
> getVworldToImagePlate(t);
> t.transform(p);
> // Then bung p through you formula
>
> However, your formula does not take into account the z component of p
> and so the final coordinates aren't where I want them to be. Any ideas?
> Have I got the wrong idea by tring to use getVworldToImagePlate()?
>
> Thanks,
>
> Jon Beniston.
>
> Some time ago you wrote:
> >
> >There is no method that does what you want to do. We'll add this in
> >the next version of Java 3D (1.2).
> >
> >For now, try the following workaround:
> >
> >xpix = xImagePlate / metersPerPixelX - canvasX
> >ypix = ScreenHeight - 1 - yImagePlate / metersPerPixelY - canvasY
> >
> >where:
> >(canvasX, canvasY) = canvas.getLocationOnScreen()
> >(ScreenWidth, ScreenHeight) = Screen Size in Pixels
> >metersPerPixelX = physicalScreenWidth / ScreenWidth
> >metersPerPixelY = physicalScreenHeight / ScreenHeight
> >
> >Let me know whether or not this works for you.
>
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/*
* @(#)LocalToWindow.java 1.2 99/02/08 15:39:12
*
* Copyright (c) 1999 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.
*/
/**
* Utility class for doing local->window transformations for case where
* Canvas3D is a simple display such as a monitor. This won't work for the
* more complex cases (i.e. a multiple canvases, head tracking, etc).
*
* Usage:
* // after the canvas and node are created
* LocalToWindow locToWindow = LocalToWindow(node, canvas);
* ...
* // when we need to transform (canvas location and node transforms may have
* // changed)
* locToWindow.update(); // make sure transforms are up to date
*
* Point3d[] localPts = <some local coords to transform >
* Point[] windowPts = <the area to put the tranformed pts >
* for (int i = 0; i < localPts.length; i++) {
* locToWindow.transformPt(localPts[i], windowPts[i]);
* }
*/
// standard j3d packages
import javax.media.j3d.*;
import javax.vecmath.*;
import java.awt.Point;
import java.awt.Dimension;
public class LocalToWindow {
Canvas3D canvas = null;
Node node = null;
// inquired/derived data
Transform3D localToVworld = new Transform3D();
Transform3D vworldToImagePlate = new Transform3D();
Transform3D localToImagePlate = new Transform3D();
Point3d eyePos = new Point3d();
int projType;
Point canvasScr;
Dimension screenSize;
double metersPerPixelX;
double metersPerPixelY;
// Temporaries
Point3d imagePlatePt = new Point3d();
Vector3d projVec = new Vector3d();
Point2d screenPt = new Point2d();
Point2d tempPt2d = new Point2d();
/**
* Creates a LocalToWindow object with no associated node or canvas.
* The node and canvas must be set before transforming points
*/
public LocalToWindow() {};
/**
* Called with the Node which specifies the local coordinates for the
* points to be transformed and the Canvas3D where the points are
* displayed
*/
public LocalToWindow(Node node, Canvas3D canvas) {
this.canvas = canvas;
this.node = node;
update();
}
/**
* Either create LocalToWindow() just before transforming points or call
* this method to ensure that the transforms are up to date. Note: if
* you are transforming several points, you only need to call this method
* once.
*/
public void update() {
if ((this.canvas != null) && (this.node != null)) {
node.getLocalToVworld(localToVworld);
canvas.getVworldToImagePlate(vworldToImagePlate);
// Make a composite transform:
// vWorldPt = LocalToVworld * localPt;
// imagePlatePt = VworldToImagePlate * vWorldPt;
// imagePlatePt = VworldToImagePlate * LocalToVworld * localPt;
localToImagePlate.mul(vworldToImagePlate, localToVworld);
// we need these to project the point from Image Plate coords to
// the actual image plate (i.e. perpsective)
canvas.getCenterEyeInImagePlate(eyePos);
//System.out.println("eyePos = " + eyePos);
projType = canvas.getView().getProjectionPolicy();
// this stuff is to go from image plate coords to window coords
canvasScr = canvas.getLocationOnScreen();
//System.out.println("canvasScr = " + canvasScr);
screenSize = canvas.getScreen3D().getSize();
double physicalScreenWidth =
canvas.getScreen3D().getPhysicalScreenWidth();
double physicalScreenHeight =
canvas.getScreen3D().getPhysicalScreenHeight();
metersPerPixelX = physicalScreenWidth / (double) screenSize.width;
metersPerPixelY = physicalScreenHeight / (double) screenSize.height;
}
}
/**
* Set the node and canvas and call update()
*/
public void update(Node node, Canvas3D canvas) {
this.canvas = canvas;
this.node = node;
update();
}
/**
* Transform the point from local coords to window coords
*/
public void transformPt(Point3d localPt, Point2d windowPt) {
// TODO: throw some kind of error if node and canvas haven't been
// set
//System.out.println("vWorld Pt = " + localPt);
localToImagePlate.transform(localPt, imagePlatePt);
//System.out.println("imagePlatePt = " + imagePlatePt);
double zScale = 1.0; // default, used for PARALELL_PROJECTION
if (projType == View.PERSPECTIVE_PROJECTION) {
// get the vector from eyePos to imagePlatePt
projVec.sub(imagePlatePt, eyePos);
// Scale this vector to make it end at the projection plane.
// Scale is ratio :
// eye->imagePlate Plane dist / eye->imagePlatePt dist
// eye dist to plane is eyePos.z (eye is in +z space)
// image->eye dist is -projVec.z (image->eye is in -z dir)
//System.out.println("eye dist = " + (eyePos.z));
//System.out.println("image dist = " + (-projVec.z));
zScale = eyePos.z / (-projVec.z);
screenPt.x = eyePos.x + projVec.x * zScale;
screenPt.y = eyePos.y + projVec.y * zScale;
} else {
screenPt.x = imagePlatePt.x;
screenPt.y = imagePlatePt.y;
}
//System.out.println("screenPt = " + screenPt);
// Note: screenPt is in image plate coords, at z=0
// Transform from image plate coords to screen coords
windowPt.x = (screenPt.x / metersPerPixelX) - canvasScr.x;
windowPt.y = screenSize.height - 1 - (screenPt.y / metersPerPixelY) -
canvasScr.y;
//System.out.println("windowPt = " + windowPt);
}
/**
* Transform the point from local coords to window coords
*/
public void transformPt(Point3d localPt, Point windowPt) {
transformPt(localPt, tempPt2d);
windowPt.x = (int)Math.round(tempPt2d.x);
windowPt.y = (int)Math.round(tempPt2d.y);
}
}
