Rotation problems

Hi guys,

Rotations on JMonkey are really giving me a headache.

I’m modeling a fiber optic and the behaviour of light in a fiber optic. It seemed like an easy task but it’s proving harder then I originally thought possible.

The blue cylinder is the fiber optic. The grey object is the direction of the light and the white line is the actual light.

The first thing I find very odd is that the rotation angle of the grey object is a positive number. As far as I know angles go counterclockwise which would make it a negative number. Why is that?

I am using the rotate method to rotate the object but I would prefer to use absolute rotation. How can I do that?

Lets say that I have a vector3f that stores a spatials x,yz rotation. How can I apply it to the spatial?



I had a very bad headache with rotations as well, Quaternions were tought to understand. I think u maybe wanna use degrees for calc the next light angle, so i hope this helps you:

[java]public static void turnTo(Node n, float angle, Vector3f witchAxis) { // (0,1,0) will rotate Y axis

Quaternion quat = new Quaternion();

quat.fromAngleAxis((FastMath.PI * angle / 180),witchAxis);



public static float getNodeAngle(Node n) {

float headAngle = (float) Math.toDegrees(n.getLocalRotation().toAngles(null)[0]); // 0 = x, 1=y, 2 = Z

if (headAngle < 0) {

headAngle += 360;


headAngle = 360 - headAngle;

return headAngle;



Then u can make the node turns to the right angle i guess

I think you want to use direction vectors instead of rotation, rotations will give you much more headaches. Really, check the tutorial I linked.

So I can create a Quaternion from an array of the angles I need. And then setting the spatial Local Rotation it will substitute the old local rotation with a this new one.

That is very helpfull. Thank you.

I actually have the lines behaving exactly like I wanted using the rotate command. The problem I was having was actually more related with the Math.Ray and Bullet Collisions affecting the behaviour of the line then with my rotation math.

But I don’t understand why the angles range from 0 to -180 in the first and second quadrants, and 0 to 180 in the 3rd 4th quadrants. Makes no sence to me.

You may have your quadrants backwards, I guess.

In the x,z plane, if you are standing upright looking into the screen then x+ is left and z+ is towards you. So a positive angle around the Y axis is counter clockwise when looking down from above… but it’s still in the first and second quadrants.

-.- … just use direction vectors, trust me.

he knows loads more then me, ill be tryng to use direction vectors as well = ~~

i’m in a hurry to get this project finished (its for school) so I’ll stick with the rotations as I seem to have gotten a handle on them But will look into direction vectors more closelly for my future (much more interesting) game dev projects :slight_smile:

Thank you all for your help.