title: Angle of Face to Camera - three.js
body: <p>If I create a geometry with just one face (triangle), like this: </p>
  
  <p>[CoffeeScript syntax]</p>
  
  <pre><code>    geometry = new THREE.Geometry()
      geometry.vertices.push(new THREE.Vector3(0, 0, 0))
      geometry.vertices.push(new THREE.Vector3(0, 10, 0))
      geometry.vertices.push(new THREE.Vector3(0, 10, 10))
      geometry.faces.push(new THREE.Face3(0, 1, 2))
      mesh = new THREE.Mesh(geometry, material)
      mesh.position.x = 10
      @scene.add(mesh)
  </code></pre>
  
  <p>And I render the scene:</p>
  
  <pre><code>    @renderer.render(@scene, @camera)
  </code></pre>
  
  <p>How can I find out what the angle of the face is to the camera?</p>
  
  <p>To clarify: If I the triangle is pointing right at the camera, so that width and hight are maximized, <a href="http://i.stack.imgur.com/yUHes.png" rel="nofollow">similar to this picture</a>, then I would expect an angle of 0deg (or 180deg).</p>
  
  <p>If the face is at a rotation to the camera where the triangle is just on line because I am looking at it exactly sideways, <a href="http://i.stack.imgur.com/HqpNQ.png" rel="nofollow">similar to this picture</a>, I would expect the angle to be 90deg (or 270deg).</p>