"Look rotation viewing vector is zero" error

Question

I have some smooth look code that spams this error. It basically makes an object look in the direction a rigidbody is moving.

 void Update()
 {
     if (target)
     {
         if (bSmooth)
         {
             Quaternion rotation = Quaternion.LookRotation((transform.position + target.rigidbody.velocity) - transform.position);
             transform.rotation = Quaternion.Slerp(transform.rotation, rotation , smoothSpeed * Time.deltaTime);
         }
         else
         {
             transform.LookAt(transform.position + target.rigidbody.velocity);
         }
     }
 }

The error is this line:

 Quaternion rotation = Quaternion.LookRotation((transform.position + target.rigidbody.velocity) - transform.position);

Answer 1

Best Answer

Answer by flaviusxvii · Feb 11, 2013 at 05:42 PM

Basic arithmetic..

(transform.position + target.rigidbody.velocity) - transform.position

(A + B) - A = B

So if B is a zero length vector (no velocity), then the function LookRotation will be mad at you.

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Owen-Reynolds · Feb 11, 2013 at 10:29 PM 3

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The common fix is to guard with "if velocity is not zero".

You want to say "if not moving, face the way I was before," and doing nothing accomplishes that.

Stardog · Feb 12, 2013 at 02:52 AM 1

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Why doesn't it like it being zero? Shouldn't it just make the rotation (0,0,0)?. It's not even a proper warning/error, just a normal Print/Debug.Log. Anyway, here is the final piece of code, with a little extra to fix something specific to my game:

 if (target.rigidbody.velocity != Vector3.zero)
 {
     Quaternion rotation = Quaternion.LookRotation((transform.position + target.rigidbody.velocity) - transform.position);
     transform.rotation = Quaternion.Slerp(transform.rotation, rotation, smoothSpeed * Time.deltaTime);
 }
 else
 {
     transform.rotation = Quaternion.Euler(Vector3.zero);
 }

flaviusxvii · Feb 12, 2013 at 03:22 AM 4

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A zero length vector allows for an infinite number of "correct" rotations, ins$$anonymous$$d of just choosing one arbitrarily, or choosing some consistent default, Unity does the only sane choice, which is to assume you're not expecting undefined results, and throwing an error.

Answer 2

Answer by supamigit · Aug 12, 2015 at 04:18 PM

I got similar issue and it was to do with i didnt declare what the OBJECT tag was so it dodnt find the v3.look rotation.... Are u doing similar to find your object to mouse?

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jchart7 · Oct 20, 2015 at 08:53 AM 0

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For those using Nav$$anonymous$$eshAgent

if (navAgent.desiredVelocity != Vector3.zero) { transform.rotation = Quaternion.LookRotation(navAgent.desiredVelocity); }

Kerihobo jchart7 · Feb 08, 2016 at 06:15 AM 0

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O$$anonymous$$G thank you, you just ended a 4hr headache for me D:

"Look rotation viewing vector is zero" error

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