Quaternion.FromToRotation to calculate Rotation between two objects

Question

I'm trying to use Quaternion.FromToRotation function to calculate the exact difference in Euler angle between two objects.

I converted the Quaternion by multiplying the simple direction vector to be used as a parameter. (http://answers.unity3d.com/questions/525952/how-i-can-converting-a-quaternion-to-a-direction-v.html)

But I couldn't get exact angle difference.

Here is code and screenshot.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class TestQuaternionFromToRotation : MonoBehaviour
 {
 
     public Transform fromTransform;
     public Transform toTransform;
     public Vector3 fromVector;
     public Vector3 toVector;
 
     void Update()
     {
         fromVector = fromTransform.rotation * Vector3.up;
         toVector = toTransform.rotation * Vector3.up;
 
         transform.rotation = Quaternion.FromToRotation(fromVector, toVector);
     }
 }

I expected (20, 40, 60), of course, but the results were different.

What's wrong with this script? Is it related to Gimbal Lock?

Answer 1

Answer by Cheerbtms · Nov 24, 2017 at 10:56 AM

I generally use FromToRotation when I want a specific part of an object to face a specific direction. For example, if I've got a robot arm facing some direction, and there's a hand attached to it at some arbitrary point, and I want to position the hand to pick up a box, I would calculate the rotation like this:

 Vector3 currentOffset = arm.transform.InverseTransformPoint(hand.transform.position);
 Vector3 desiredOffset = arm.transform.InverseTransformPoint(box.transform.position);
 arm.transform.localRotation *= Quaternion.FromToRotation(currentOffset, desiredOffset);

Hope that helps someone!

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Bonkahe · Dec 06, 2021 at 05:51 AM 0

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This worked perfectly for me, thank you very much.

Quaternion.FromToRotation to calculate Rotation between two objects

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