Manual Quaternions

Question

For some reason I can't seem to wrap my head around this problem. Basically I have a series of quaternion orientations being supplied to Unity3D from an external program. The orientations are being pulled from a mocap system I'm using.

The orientations I get from the system are relative to a single global coordinate system. So they aren't related to any sort of parent transform.

The problem that I'm having is that I can't figure out where to supply my transformations. Because they aren't cumulative (IE, each orientation I get is the actual orientation and not the change since the last one) I can't use the update methods supplied.

Answer 1

Best Answer

Answer by bruceb · Feb 15, 2010 at 03:45 PM

Here is the snippet of code that will give the localRotation of a child relative to its parent if you have the 2 world rotations.

childObj.transform.localRotation = Quaternion.Inverse(childObj.transform.parent.rotation) * theChild.transform.rotation

Add comment · Share

Answer 2

Answer by Jaap Kreijkamp · Feb 14, 2010 at 11:16 PM

You could convert the absolute rotation to a relative rotation by multiplying it with the inverse of the current rotation.

Add comment · Show 1 · Share

Jerdak · Feb 14, 2010 at 11:34 PM 0

Share

Hmm, I'm a touch confused. Doesn't that just subtract out the current rotation from the absolute rotation? So if I've already rotated 45 degrees about X and I tell it to rotate 90 about X it will only rotate another 45?

This is fine except for 2 things: 1.) The current rotation of my object's limb was set in 3DS $$anonymous$$ax. So the base rotation for the arm, for example, is already at Euler(5,5,0). When I rotate that by 90 around X it should be 90 + what I already have. 2.) This doesn't seem take in to account if I rotate my person in the scene.

Answer 3

I'll be the first to admit my understanding of all of this is tenuous at best.

The following is my solution. Visually it seems to work as I want. The part I find slightly off is the conversion of the quaternion axis by the current base orientation. I did this on a whim to see what would happen. Oh and for some reason it won't rotate about the x-axis unless I update the z value of my quaternion?

public class Keyboard : MonoBehaviour { public GameObject objArm; public GameObject pivot; private Vector3 objPosition; private Quaternion objRot; private Quaternion lastRot = Quaternion.identity;

 private float rot = 0.0f;
 private int rotDir = 1;
 public float rotationIncr = 0.1f;

 private bool updateFromParent = false;
 ///Called from MouseLook.cs to tell player controller it's base orientation is in need of update
 void UpdateRotationFromParent(){
     objArm.transform.rotation = pivot.transform.rotation;
     objRot = objArm.transform.rotation;
     updateFromParent = true;
     RotateArm(lastRot);
 }
 // Use this for initialization
 void Start () {
     Screen.showCursor = false;
     Screen.lockCursor = true;
     UpdateRotationFromParent();
 }

 // Update is called once per frame
 void Update () {
     if (Input.GetKey ("escape")) {
         Application.Quit();
     }
     UpdateArm();
 }
 void RotateArm(Quaternion q){
     float angle = 0.0f;
     Vector3 axis = Vector3.zero;

     q.ToAngleAxis(out angle, out axis);

     ///Reorient axis of rotation to current object rotation
     axis = objRot * new Vector3(axis.x,axis.y,axis.z);

     //print("Rot: " + rot + " Axis: " + axis + " Angle: " + angle + " objRot: " + objRot);
     objArm.transform.rotation = objRot;
     objArm.transform.RotateAround(pivot.transform.position,axis,angle);
 }
 void UpdateArm () {
     {    ///Update rotation to simulate movement about Z axis from 0-90
         rot += rotationIncr * (float)rotDir;
         if(rot &gt; 90.0f || rot &lt; 0.0f){
             rotDir *= -1;
         }
     }

     ///
     Quaternion q = Quaternion.Euler(rot,0.0f,0.0f);
     lastRot = q;
     RotateArm(q);
 }

}

Manual Quaternions

3 Replies

Your answer

Follow this Question

Related Questions