java3d orbits

[mgriffith]

i have a question... i can't get my orbits to align right in java3d. it's for a satellite application, but just by hand, i can't get an x, y, and z rotation of a vertical rotation axis to create what i think it should.

do you see any problems with the following functions? advice?? comments??

-----------------------

    //add satellite to branchgroup given inclination, raan, semi-major axis, and period
    public int addSatellite(double inclination, double raan, double sma, double period)
    {
    	SATELLITE_COUNT++;
	
	// First, find the point of the orbit which crosses the y-z plane
	double x1 = 0;
	double y1 = sma * Math.sin(inclination);
	double z1 = sma * Math.cos(inclination);

	// Next, find the point of the orbit which crosses the x-z plane
	double x2 = sma * Math.cos(raan);
	double y2 = 0;
	double z2 = sma * Math.sin(raan);

	// Now that we have two position vectors on the orbital plane,
	// we can cross product them to find the normal vector to that plane
	double x3 = sma * sma * Math.sin(inclination) * Math.sin(raan);
	double y3 = - (sma * sma * Math.cos(inclination) * Math.cos(raan));
	double z3 = sma * sma * Math.sin(inclination) * Math.cos(raan);

	// We must also convert the vector we just calculated to a vector of angles
	double angx = Math.atan(z3/y3);
	double angy = raan;
	double angz = Math.atan(y3/x3);

	Vector3d trans = map(new Vector3d(x1,y1,z1));

    	sat.addElement( getSatellite(
		trans.x, trans.y, trans.z, angx, angy, angz, period
	) );

	BranchGroup bg = new BranchGroup();
	bg.addChild( (TransformGroup)sat.elementAt(SATELLITE_COUNT-1) );
	objRoot.addChild(bg);

    	return SATELLITE_COUNT-1;
    }

    //create a satellite given an initial position, axis of rotation, and period of rotation
    private TransformGroup getSatellite(double x, double y, double z, double angleX, double angleY, double angleZ, double period) {
    	TransformGroup sat1RotTrans = new TransformGroup();
	sat1RotTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
	sat1RotTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
	sat1RotTrans.setCapability(TransformGroup.ALLOW_CHILDREN_READ);

	// Set the satellite's properties
	Transform3D t = new Transform3D();
	Vector3d satPos1 =  new Vector3d(x, y, z);
	t.set(satPos1);
	TransformGroup sat1Trans = new TransformGroup(t);
	sat1Trans.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
	sat1Trans.setCapability(TransformGroup.ALLOW_CHILDREN_READ);
	sat1RotTrans.addChild(sat1Trans);


	Material m = new Material();
	Appearance appSat1 = new Appearance();
	m.setLightingEnable(true);
	ColoringAttributes caSat1 = new ColoringAttributes();
	caSat1.setColor(satColor1);
	appSat1.setColoringAttributes(caSat1);
	appSat1.setMaterial(m);

	sat1Trans.addChild(
		new Sphere(0.02f, appSat1)
	);

	//create axis of rotation
	Transform3D rotAxis = new Transform3D();
	Transform3D rotX = new Transform3D();
	rotX.rotX(angleX);
	rotAxis.mul(rotX);
	Transform3D rotY = new Transform3D();
	rotY.rotY(angleY);
	rotAxis.mul(rotY);
	Transform3D rotZ = new Transform3D();
	rotZ.rotZ(angleZ);
	rotAxis.mul(rotZ);

	//create rotation interpolation
	if (period > 0) {
		Alpha rotor1Alpha = new Alpha(
		     -1, (int)(1000*period)
		);
		RotationInterpolator rotator1 = new RotationInterpolator(
		     rotor1Alpha, sat1RotTrans, rotAxis,
		     0.0f, (float) Math.PI*2.0f
		);
		rotator1.setSchedulingBounds(bounds);
		sat1RotTrans.addChild(rotator1);
	}

	return sat1RotTrans;
    }

----------------------

thanks for any help

 

[sedj]

Have you tried the Java3D mailing list at Sun ?

http://archives.java.sun.com/archives/java3d-interest.html