How would I interpret angular displacement from target rotation to max out at 180°?

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I have two rotations, the objects current rotation, and the target objects rotation. I would like to create a single float that increases as the two rotations differ maxing out at 180° (facing opposite directions). I spent a long time looking into options and found "ToAngleAxis". This lets me grab a single number for the rotations and use that to find the difference.

Bear with me as this gets a little confusing - but the problem is that when the object is facing the opposite direction the displacement is 180° - but if it continues to rotate towards the target rotation it goes all the way to 360° instead of back down to zero.

Anyone have any ideas on how to get the displacement to max out at 180° and go back down to zero as it turns in a full circle?

Here's my code that will work with two cubes if you want to test out my problem:

     public Transform target;
     float curAngle;
     Vector3 curAxis;
     float targAngle;
     Vector3 targAxis;
 
     void Update () {
         transform.rotation.ToAngleAxis(out curAngle, out curAxis);
         target.rotation.ToAngleAxis(out targAngle, out targAxis);
         double displacement = 1-(curAngle-targAngle);
         Debug.Log(displacement);
     }

Aren't rotations FUN?!??!?

In case anyone is wondering WHY I'm trying to do this -- I'd love to sync the pitch of an audio source to how closely it's looking towards the player.

Answer 1

Best Answer

Answer by wyatts · Oct 21, 2017 at 12:19 AM

Thanks Harinezumi! Wow I can't believe I overlooked this. Such a simple tool!!! Definitely simplifies my approach, yet it returned the same result (it goes to 360 instead of maxing out at 180). I actually found a nice bit of code that just maths the numbers over 180 back down :)

     public Transform target;
     public float angleOut;
 
     void Update () {
         var displacement = Quaternion.Angle(target.rotation, transform.rotation);
         angleOut = ClampAngle(displacement, 0, 180);
         Debug.Log(angleOut);
     }
 
     float ClampAngle(float angle, float from, float to) {
         if(angle >180) angle = 360 - angle;
         angle = Mathf.Clamp(angle, from, to);
         if(angle <0) angle = 360 + angle;
         return angle;
     }

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Answer 2

Answer by Harinezumi · Oct 20, 2017 at 07:56 AM

Hey @wyatts! I'm not sure this is what you want, but Quaternion.Angle() gives you the angle between 2 rotations, clamped to a value between 0 and 180, so if you divide it by 180 you'll get a float between [0, 1], maxing out at 180.

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Answer 3

Answer by pako · Oct 20, 2017 at 07:27 AM

Maybe you can use the vector dot product to achieve what you want. Vector3.Dot returns a float between 1 and -1 for normalized vectors. -1 meaning they are pointing in opposite directions, i.e 180deg apart:

https://docs.unity3d.com/ScriptReference/Vector3.Dot.html

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wyatts · Oct 21, 2017 at 12:25 AM 0

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Thanks for this! It could work, but the Quaternion.Angle() approach was a bit more direct. Cheers!

How would I interpret angular displacement from target rotation to max out at 180°?

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