Hi,
Seeing as your question follows two others that are similar, I decided to
give you a few short code clips. The methods below are from a program where I
needed to periodically move the viewer to a new nearby location. I did this by
keeping track of three parameters; a point where the viewer (camera)is at, the
point that the camera is looking towards, and a vector which defines the up
direction on the screen (initially new Vector3d(0.0d, 1.0d, 0.0d) ). Note that
if I tilt the camera up or down, then the 'up vector' is no longer perpendicular
to the direction you are looking. To correct that I cross the up vector with
the look direction which gives me a new left/right vector perpendicular to the
other two. I then reverse the process and cross the left/right vector with the
look direction to give a corrected up dirction which is now perpendicular to the
view. Note that there will be subtle differences between each of the methods
you implement for the different move/tilt options.
Hope this helps some of you newer guys out there, but I suggest you take a
look at some of the graphic texts available. To work in Java 3D you really need
to have at least a basic understanding of coordinate systems, vectors and
matrix math.
- Gary Graf
/**
* This method will change the views position (from point) and rotate it
* about the look at point in such a manner that it appears the viewer is
* moving perpendicularly left with respect to the object and field of view.
*
* @param stepSize - An integer which is the number of degress of rotation
* about the view point (look at point) that the image will be moved.
*/
public void moveLeft(int stepSize){
double rotInRadians = -(stepSize * degreeToRadian);
//Translate fromPoint to position relative to center of rotation (toPoint)
fromPoint.sub(toPoint);
//Move camera in orbit to left
AxisAngle4d rotAxis = new AxisAngle4d(upDirection, rotInRadians);
Matrix3d rotMatrix = new Matrix3d();
rotMatrix.set(rotAxis);
rotMatrix.transform(fromPoint);
fromPoint.add(toPoint);
positionCamera();
} //end moveLeft()
/**
* This method will change the views position (look at point) and rotate it
* about the viewer's position in such a manner that it appears the viewer
* tilting his head up with respect to the object and field of view.
*
* @param stepSize - A float which is the number of degrees of rotation
* about the viewer's position that the image will be moved.
*/
public void tiltUp(float stepSize){
Vector3d rightDir = new Vector3d();
double rotInRadians = -(stepSize * degreeToRadian);
//Find original look direction vector
Vector3d lookDir = new Vector3d(fromPoint);
lookDir.sub(toPoint);
//Compute an orthagonal vector to later rebuild the up vector
rightDir.cross(lookDir, upDirection);
rightDir.normalize();
//Translate fromPoint to position relative to center of rotation (toPoint)
toPoint.sub(fromPoint);
//Rotate the to point to effect the tilt
AxisAngle4d rotAxis = new AxisAngle4d(rightDir, rotInRadians);
Matrix3d rotMatrix = new Matrix3d();
rotMatrix.set(rotAxis);
rotMatrix.transform(toPoint);
toPoint.add(fromPoint);
//Compute new up vector
lookDir = new Vector3d(fromPoint);
lookDir.sub(toPoint);
upDirection.cross(rightDir, lookDir);
upDirection.normalize();
positionCamera();
} //end tiltUp()
/**
* This method moves the viewer's position to the most currently defined
* from point and orients the view towards the targeted look point
* (originally the object center).
* the upper left corner of the view.
*/
public void positionCamera(){
//Set the camera to the new location
Transform3D viewRotTrans = new Transform3D();
viewRotTrans.lookAt(fromPoint, toPoint, upDirection);
viewRotTrans.invert();
// Note: viewTransGrp =
universe.getViewingPlatform().getViewPlatformTransform();
viewTransGrp.setTransform(viewRotTrans);
} //end positionCamera()
J�rgen Vansteelant wrote:
> Helo,
>
> can someone explain me the method lookAt(Point3d eye, Point3d center,
> Vector3d up)
> I think I might use it , but I have some problems with the vector parameter.
>
> If anyone has an example that uses this method ,please post it if you want!
>
> Thank you.
> Jurgen
>
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