Rotate vector using Java 3D

Question

I'm attempting to use Java3D to rotate a vector. My goal is create a transform that will make the vector parallel with the y-axis. To do this, I calculated the angle between the original vector and an identical vector except that it has a z value of 0 (original x, original y, 0 for z-value). I then did the same thing for the y-axis (original x, 0 for y-value, original z). I then used each angle to create two Transform3D objects, multiply them together and apply to the vector. My code is as follows:

Transform3D yRotation = new Transform3D();
Transform3D zRotation = new Transform3D();

//create new normal vector
Vector3f normPoint = new Vector3f (normal.getX(), normal.getY(), normal.getZ());

//****Z rotation methods*****
Vector3f newNormPointZ = new Vector3f(normal.getX(), normal.getY(),0.0F);
float zAngle = normPoint.angle(newNormPointZ);
zRotation.rotZ(zAngle);

//****Y rotation methods*****
Vector3f newNormPointY = new Vector3f(normal.getX(),0.0F, normal.getZ());
float yAngle = normPoint.angle(newNormPointY);
yRotation.rotY(yAngle);

//combine the two rotations
yRotation.mul(zRotation);

System.out.println("before trans normal = " +normPoint.x + ", "+normPoint.y+", "+normPoint.z);
//PRINT STATEMENT RETURNS: before trans normal = 0.069842085, 0.99316376, 0.09353002

//perform transform 
yRotation.transform(normPoint);

System.out.println("normal trans = " +normPoint.x + ", "+normPoint.y+", "+normPoint.z);
//PRINT STATEMENT RETURNS: normal trans = 0.09016449, 0.99534255, 0.03411238

I was hoping the transform would produce x and z values of or very close to 0. While the logic makes sense to me, I'm obviously missing something..

maher.cs maher.cs · Accepted Answer · 2011-06-23T20:01:33

If your goal is to rotate a vector parallel to the y axis, why can't you just manually set it using the magnitude of the vector and setting your vector to <0, MAGNITUDE, 0>?

Also, you should know that rotating a vector to be directly pointing +Y or -Y can cause some rotation implementations to break, since they operate according to the "world up" vector, or, <0,1,0>. You can solve this by building your own rotation system and using the "world out" vector <0,0,1> when rotating directly up.

If you have some other purpose for this, fastgraph helped me with building rotation matrices.

It's best to understand the math of what's going on so that you know what to do in the future.

Rotate vector using Java 3D

1 Answers