LookAt To Only Rotate on Y Axis - How?

Hi All,

While Michael's above code should work. Manually modifying transform.rotation is not the recommended Unity way to rotate an object.

It is in fact possible to limit the axes which rotate using transform.LookAt(). Please see the following code which limits rotation to the Y axis only:

 Vector3 targetPostition = new Vector3( target.position.x, 
                                        this.transform.position.y, 
                                        target.position.z ) ;
 this.transform.LookAt( targetPostition ) ;

At a basic level the LookAt() function calculates rotational values for the object you want to rotate (transform) based on the positional values of the object you want to look at (target). The key benefit to LookAt() is that it ensures your transform always faces the target, calculating the necessary rotational values accordingly.

All the above code is really saying is: "calculate the rotational values for the transform based on the target's X and Z positions (horizontal plane), but the target's Y position will always be the same as mine." E.g. the same height as me. The resulting calculation forces the transform to face in the direction of the target but believes the target is at the same height of the transform. Thus preventing vertical rotation.

This is my interpretation of it anyway. If anyone can provide further detail I would really welcome it!

[4]: http://answers.unity3d.com/users/5636/oliver-jones.html

Take a look at this (http://answers.unity3d.com/questions/566152/lookat-locked-at-y-axis-but-in-local-space.html)

In summary for those of us that want to rotate for example a turret around its local y axis when said turret can be mounted at an angle in world space the above solution does the trick.

What its doing is similar but projects the point on a plane local to the turret or whatever you are rotating. Below is my implementation for a turret system.

 //Project to plane
         float distanceToPlane = Vector3.Dot(selfTransform.up, position - selfTransform.position);
         Vector3 pointOnPlane = position - (selfTransform.up * distanceToPlane);
 
         selfTransform.LookAt(pointOnPlane, selfTransform.up);

I had similar problem and every answers what i found here arent entirely true, becouse other answers here change X and Z axis too. If you want change only Y axis and do not interfere with others axis, you need do something like this:

 var lookPos = target.transform.position - transform.position;
             Quaternion lookRot = Quaternion.LookRotation(lookPos);
             lookRot.eulerAngles =new Vector3(transform.rotation.eulerAngles.x, lookRot.eulerAngles.y, transform.rotation.eulerAngles.z);
             transform.rotation = Quaternion.Slerp(transform.rotation, lookRot, Time.deltaTime * speedOfrotation);

Now objects change only Y axis and can rotate by physics on other Axes.

To look at the object and only rotate at y axis:

 void Update() 
 {
     Vector3 lookPos = target.position - transform.position;
     Quaternion lookRot = Quaternion.LookRotation(lookPos, Vector3.up);
     float eulerY = lookRot.eulerAngles.y;
     Quaternion rotation = Quaternion.Euler (0, eulerY, 0);
     transform.rotation = rotation;
 }