getCameraPosition(vec3 ) {
    vec3 = vec3 || new Vector3()
    this.notifyWorld('getCameraPosition', vec3)
    return vec3
  }
Get the current position vector of the world's camera.
@param {Vector3} [vec3] - optional Vector3 object to populate with the position;
                 if not passed in a new one will be created.
@returns {Vector3}