Unity/3d/3dから2dの座標変換

LabelPosition.cs

using UnityEngine;
public class LabelPosition : MonoBehaviour
{
    [SerializeField]
    public Camera mainCamera, uiCamera;
    [SerializeField]
    public GameObject cube;
    [SerializeField]
    public Canvas canvas;

    void Update()
    {
        var pos = Vector2.zero;
        var worldCamera = mainCamera;
        var canvasRect = canvas.GetComponent<RectTransform>();

        Vector3 position =
            new Vector3(
                cube.transform.position.x,
                cube.transform.position.y + 1f,
                cube.transform.position.z
                );
        var screenPos = RectTransformUtility.WorldToScreenPoint(worldCamera, position);
        RectTransformUtility.ScreenPointToLocalPointInRectangle(canvasRect, screenPos, uiCamera, out pos);
        this.GetComponent<RectTransform>().localPosition = pos;
    }
}

呼び出し方サンプル

Example.cs

void LabelCall() {
        Camera camera = GameObject.Find("FPS Camera").GetComponent<Camera>();
        GameObject zombie = GameObject.Find("Zombie" + wordcnt + "Object");
        GameObject obj = GameObject.Find("NewText");
        LabelPosition labelPosition = obj.GetComponent<LabelPosition>();
        labelPosition.mainCamera = camera;
        labelPosition.uiCamera = camera;
        labelPosition.cube = zombie;
        labelPosition.canvas = GameObject.Find("Canvas").GetComponent<Canvas>();
}

参考：http://tsubakit1.hateblo.jp/entry/2016/03/01/020510