How to use Graphic Raycaster with WorldSpace UI?

From Unity docs:

The Graphic Raycaster is used to raycast against a Canvas. The Raycaster looks at all Graphics on the canvas and determines if any of them have been hit.

You can use EventSystem.RaycastAll to raycast against graphics(UI) elements.

Here is a short example for your case:

void Update() {


// Example: get controller's current orientation:
  Quaternion ori = GvrController.Orientation;

  // If you want a vector that points in the direction of the controller
  // you can just multiply this quat by Vector3.forward:
  Vector3 vector = ori * Vector3.forward;

  // ...or you can just change the rotation of some entity on your scene
  // (e.g. the player's arm) to match the controller's orientation
  playerArmObject.transform.localRotation = ori;

  // Example: check if touchpad was just touched
  if (GvrController.TouchDown) {
    // Do something.
    // TouchDown is true for 1 frame after touchpad is touched.

    PointerEventData pointerData = new PointerEventData(EventSystem.current);

    pointerData.position = Input.mousePosition; // use the position from controller as start of raycast instead of mousePosition.

    List<RaycastResult> results = new List<RaycastResult>();
    EventSystem.current.RaycastAll(pointerData, results);

    if (results.Count > 0) {
         //WorldUI is my layer name
         if (results[0].gameObject.layer == LayerMask.NameToLayer("WorldUI")){ 
         string dbg = "Root Element: {0} \n GrandChild Element: {1}";
         Debug.Log(string.Format(dbg, results[results.Count-1].gameObject.name,results[0].gameObject.name));
         //Debug.Log("Root Element: "+results[results.Count-1].gameObject.name);
         //Debug.Log("GrandChild Element: "+results[0].gameObject.name);
          results.Clear();
     }
   }
}

The above script is not tested by myself. So there might be some errors.

Here are some other references to help you understand more:

1. Graphics Raycaster of Unity; How does it work?
2. Raycast against UI in world space
3. How to raycast against uGUI objects from an arbitrary screen/canvas position
4. How do you perform a Graphic Raycast?
5. GraphicRaycaster

Hope it helps.

Umair M's current suggestion doesn't handle the fact that the ray is originating in world space and traveling at an angle.

It doesn't look to me like you can do a GUI raycast in world space at an angle even if your canvas is in world space. This page suggests a technique of creating a non-rendering camera, moving it around in 3D space with the ray you want to cast, and then doing the GUI raycast relative to that camera. I haven't tried it yet, but it sounds promising.