Yes, that makes sense,

I have an array of "jellyfish" that randomly move around the world, however, once they are a certain distance away, I need them to come back into the centre of the camera view.  I'm struggling to see how I can derive the correct rotation that points to the centre of the camera view.(the camera is static)


private void animate()
    {
        if (aniFrame > 0)
        {
            ind += INC_FRACTION * aniFrame;

            if (ind > 1) {
                ind -= 1;
                aniFrame = 0;
            }
            for (int i = 0; i < jellyFishAmount; i++)
            {
                jellyFishClones[i].animate(ind);                //apply the new animation frame
                movedDistance[i] += MOVE_SPEED;                 //increase the directional change
                if (roam[i]&&aniFrame%2==0)                     //only change direction every second call and if the jellyfish hasn't left the "safe area"
                {
                    jellyFishClones[i].rotateX(random.nextFloat()*0.5f);
                    jellyFishClones[i].rotateY(random.nextFloat()*0.5f);
                }
                if (centerVec.distance(jellyFishClones[i].getTranslation()) > 200f)
                {
                    if (roam[i])
                    {
                        jellyFishClones[i].rotateX(centerVec.calcAngle(jellyFishClones[i].getXAxis()));
                        jellyFishClones[i].rotateY(centerVec.calcAngle(jellyFishClones[i].getYAxis()));
                        jellyFishClones[i].rotateZ(centerVec.calcAngle(jellyFishClones[i].getZAxis()));
                        //jellyFishClones[i].clearTranslation();
                        movedDistance[i] = 0;     
                    }
                    roam[i] = false;
                    if (centerVec.distance(jellyFishClones[i].getTranslation()) < 10f)
                    {
                        roam[i] = true;                         //set the jellyfish back to randomly roaming
                    }
                }
                directionalVec[i] = jellyFishClones[i].getZAxis();         
                directionalVec[i].scalarMul(movedDistance[i]);             
                jellyFishClones[i].translate(directionalVec[i]);           
            }
       }
}


Changing the first vector's Z value from 0 to a negative number returns a correct value;


                v=new SimpleVector(0f,0f,-10f);
                ov=new SimpleVector(0f,0f,10f);

Now I get:

I/jPCT-AE: angle:3.1415927

which I was expecting from 0 also

Is it impossible to calculate an angle with one vector having an absolute value of 0?

Hi, Can someone help me?

I am trying to calculate the angle between two vectors, but the only results I get are "NaN". I am sure it is something I am doing wrong...

     
v=new SimpleVector(0,0,0);
ov=new SimpleVector(1,1,10);
float angle = v.calcAngle(ov);
Logger.log("angle:"+String.valueOf(angle));


The Android Monitor just outputs:

I/jPCT-AE: angle:NaN