How to convert from world space to canvas space?

I hadn't the time to play around with the beta yet. So i can't say much about the new UI system, but the canvas and the RectTransform positions are pure screenspace / canvas coordinates and have no relation to "worldspace". Worldspace coordinates are actually mapped to screenspace / viewspace coordinates when rendered by a camera. If you want to know the screen / view space coordinate of a worldspace object, you have to use Camera.WorldToScreenPoint or Camera.WorldToViewportPoint of the camera that renders that object.

If you have the position in screenspace you might want to use the RectTransform $$anonymous$$erarchy to get it as a relative position wit$$anonymous$$n a certain area.

I solved t$$anonymous$$s problem by doing the following:

 //t$$anonymous$$s is your object that you want to have the UI element hovering over
 GameObject WorldObject;
 
 //t$$anonymous$$s is the ui element
 RectTransform UI_Element;
 
 //first you need the RectTransform component of your canvas
 RectTransform CanvasRect=Canvas.GetComponent<RectTransform>();
 
 //then you calculate the position of the UI element
 //0,0 for the canvas is at the center of the screen, whereas WorldToViewPortPoint treats the lower left corner as 0,0. Because of t$$anonymous$$s, you need to subtract the height / width of the canvas * 0.5 to get the correct position.
 
 Vector2 ViewportPosition=Cam.WorldToViewportPoint(WorldObject.transform.position);
 Vector2 WorldObject_ScreenPosition=new Vector2(
 ((ViewportPosition.x*CanvasRect.sizeDelta.x)-(CanvasRect.sizeDelta.x*0.5f)),
 ((ViewportPosition.y*CanvasRect.sizeDelta.y)-(CanvasRect.sizeDelta.y*0.5f)));
 
 //now you can set the position of the ui element
 UI_Element.anchoredPosition=WorldObject_ScreenPosition;

RectTransform.GetLocalCorners(Vetor3[] array) will fill out an array with 4 elements. T$$anonymous$$s gives you in world space how big the canvas is.

T$$anonymous$$s issue also has another solution:

 Vector2 pos = gameObject.transform.position;  // get the game object position
 Vector2 viewportPoint = Camera.main.WorldToViewportPoint(pos);  //convert game object position to VievportPoint
 
 // set MIN and MAX Anchor values(positions) to the same position (ViewportPoint)
 rectTransform.anchorMin = viewportPoint;  
 rectTransform.anchorMax = viewportPoint; 

 

T$$anonymous$$s is the cleanest way I can find of making a UI element follow a world object's 3D position.

 public RectTransform canvasRectT;
 public RectTransform healthBar;
 public Transform objectToFollow;

 void Update()
 {
     Vector2 screenPoint = RectTransformUtility.WorldToScreenPoint(Camera.main, objectToFollow.position);

     healthBar.anchoredPosition = screenPoint - canvasRectT.sizeDelta / 2f;
 }

Reading Sylos's answer above helped.