title: AR.js distorted perspective: How to use a personalized camera calibration file `camera_para.dat` so that the "floor" plane is horizontal?
body: <p>I'm looking into <a href="https://github.com/jeromeetienne/AR.js/" rel="nofollow noreferrer">AR.js</a> for an augmented reality use case where 3D objects do not appear directly <em>on</em> the hiro marker, but somewhere <em>around</em> the marker.</p>
  
  <p>When I view my AR scene through my iPhone 7 from the top, everything looks fine, but when I tilt my camera to get more perspective, AR.js doesn't apply the same perspective to the AR world so that distant virtual objects appear as if they were located on an inclined plane.</p>
  
  <p>I created an <a href="https://github.com/PierreFritsch/AR.js/tree/calibration/three.js/examples/calibration" rel="nofollow noreferrer">example page</a> to illustrate this behaviour: When viewed from above, the grids match perfectly, but when viewed from the side, the planes mismatch. </p>
  
  <p><a href="https://i.stack.imgur.com/toSCl.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/toSClm.jpg" alt="AR scene, seen from the top"></a>
  <a href="https://i.stack.imgur.com/cLHdd.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cLHddm.jpg" alt="AR scene, seen from the bottom side"></a></p>
  
  <p>Are there any settings I can apply to configure AR.js (or <a href="https://github.com/artoolkit" rel="nofollow noreferrer">ARToolKit</a>, which it depends on)? Maybe there's a way to define the field of view of my webcam there?</p>
  
  <p>[EDIT] One week later, I would reword my question to: How can I use a device-specific <code>camera_para.dat</code> ARToolkit camera calibration file in AR.js without generating side effects such as a distorted rendering?</p>