How to rotate an object so that y axis faces towards another object?

[guitarxe]

Can someone help me understand what is the math required to rotate one object so that it’s UP vector (the local y-axis) points towards another object?

I know that Transform.LookAt does that, but for the FORWARD vector (the local z-axix), but I want to do the same for the y-axis instead, with some slight modification (dampening how fast it can rotate)

[EvilTak]

Looking at your comment on the other answer, you should use Quaternion.FromToRotation. And after that, use Quaternion.Lerp. Something like this (This code should be in FixedUpdate for smooth results):

Vector3 direction = otherObject.position - transform.position;
Quaternion toRotation = Quaternion.FromToRotation(transform.up, direction);
transform.rotation = Quaternion.Lerp(transform.rotation, toRotation, speed * Time.time);

Here is the result (A cylinder poinsting towards the main camera with speed = 0.1f):

[Kartik1607]

Hey.

Lets try some coding.

First, we create a public Transform variable to store the target object. (to whom we want to look)

public Transform target;

Now, we want to look at the target.
So, we use LookAt function.

	void Update () {
		transform.LookAt (target.position);
	}

This produces this effect.

But, we want the Y axis to point to cube.

If we observe, we can see that Y axis is 90 degree to the direction tree is looking at.
So, we simply rotate the tree by 90 degree around X axis.

	void Update () {
		transform.LookAt (target.position);
		transform.Rotate (new Vector3 (1.0f, 0, 0), 90);
	}

This makes Y axis point towards the object.