title: Three.js: how to put objects to the top of the screen with same size
body: <p>I am new on threejs, and I don't know this question is absolutely basic or it is too advanced.
  So, I want to put some objects to the top left corner of the screen. The next object is always goes to the next right position. I need to every object looks like same size. How can I calculate their 3d positions and scales (if need)</p>
  
  <p>I find a solution, which maybe good for me: <a href="https://stackoverflow.com/questions/16226693/three-js-show-world-coordinate-axes-in-corner-of-scene">Three.js: Show world coordinate axes in corner of scene</a> but I think the second canvas is too big overhead - and it cover the original canvas.</p>
  
  <p>I think create a sphere which position is the camera position, and the radius is bigger than screen-camera distance, and with a raycaster find the intersection, and that is the point. Is this a good way?</p>
  
  <p>My objects are arrows (poly and extruded) and they shows the selected directions for my user. So this helper is an information box, but I don't want to cover the original scene. For example 10-12 arrow at the top of the screen. And it need to same size to be beauty.</p>