Calculate sum over all movements and rotations of object

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Hello everybody,

I'd like to do a statistic for my application in which the user can move and rotate an object. In the end I would like to display how far the object has been moved overall and how much the user has rotated the objects.

For the change in position I have the straight forward approach of always adding the change in the objects position to one Vector3 holding the distance in the 3 axis overall. I do this in the Update() method:

 if (transform.hasChanged){
     overallMovedDist  += vector3.Distance(oldPosition, transform.position);
     old.position = transform.position;
     transform.hasChanged = false;
 }

Now for the rotation I wonder, how one would best approach such a statistic? For users it would probably be best to display the values in Eulerangles, I suppose. So after doing two full rotations around for instance the x-axis one would get something like (4*pi, 0, 0) or (2*360, 0,0) as a result: With the same approach as for the position I first tried to calculate this by always directly comparing the change in eulerangles that I got from the quaternions. However if an object is rotated around one axis too far, you get a jump in the values for the other axis as well as some point. If I am correct, this comes from the fact that Unity uses Quaternions internally and the conversion. I tried some stuff with Quaternions already which you can see beneath.

 Quaternion relativeChange = Quaternion.Inverse(oldRotation) * transform.rotation; // get rotation between old and new transform.rotation
 overallRotation = overallRotation * relativeChange; //add the two Quaternions
 oldRotation = transform.rotation;
 Debug.Log(overallRotation.ToEulerAngles());

However when I test this in my code, slowly rotate the object around an axis and watch the Log I always get the same thing printed, which is (0.0, 0.0, 0.0). But obviously this is not correct, as I have rotated the object.

Can anybody assist me with how to approach this correctly? Thank you in advance!

Answer 1

Answer by DenisIsDenis · Jun 30, 2021 at 03:11 AM

Why don't you use Vector3 to store the rotation already at the Euler angles. The algorithm is similar to measuring the coordinate change:

 Vector3 overallRotation, oldRotation;
     void Start()
     {
         oldRotation = transform.rotation.eulerAngles;
     }
 
     void Update()
     {
         if (oldRotation != transform.rotation.eulerAngles)
         {
             overallRotation += transform.rotation.eulerAngles - oldRotation;
             oldRotation = transform.rotation.eulerAngles;
             print(overallRotation);
         }
     }

The angle size will be between 0 and 360 (because transform.rotation.eulerAngles has such borders).

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JustAnotherRobot · Jul 02, 2021 at 10:21 AM 0

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Thank you for your response. I tried to share the issue I have with this approach in the original question, however I probably did not do a good job describing it.

However if an object is rotated around one axis too far, you get a jump in the values for the other axis as well as some point

If I use the eulerangle code, and continuously rotate the object around the same axis (like ai$$anonymous$$g to turn it 360 degrees), this is the output for the overallRotation I get at first is along the lines of:

(1.0, 0.0, 0.0) (2.0, 0.0, 0.0) (3.0, 0.0, 0.0)

But when getting for instance close to 90 degree rotation we got the following switch:

(88.0, 0.0, 0.0) (89.0, 0.0, 0.0) (90.0, 0.0, 0.0) (88.0, 180.0, 180) (87.0, 180.0, 180.0)

DenisIsDenis JustAnotherRobot · Jul 02, 2021 at 12:00 PM 0

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You can approach the issue from the other side. After all, you somehow implement object rotation for users. Then why not use this: for sure you implement rotation for each axis separately. Then you can write something like this:

 // for x-axis
 transform.Rotate(xAngle, 0, 0);
 overallRotation.x += xAngle; // overallRotation is Vector3

DenisIsDenis · Jul 02, 2021 at 11:05 AM 0

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For your method with Quaternion to work, you need to initialize the overallRotation (because simply declaring it, it contains null, and when multiplied by null, we get null):

  overallRotation = Quaternion.Euler (0, 0, 0);

But, unfortunately, even with the use of Quaternions, you will get the problem you indicated (I also have it).

Calculate sum over all movements and rotations of object

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