title: Get BoundingBox of ONLY visible area of map in osmdroid
body: <p>I am using osmdroid version 4 and I want to have BoundingBox of visible map. It seems that <code>MapView.getBoundingBox</code> method returns bounding box of all tiles that are visible or partially visible. Take a look at this picture: </p>
  
  <p><img src="https://i.stack.imgur.com/b0oYY.png" alt="enter image description here"></p>
  
  <p>Black rectangles are tiles, red rectangle with rounded corners is  device display.</p>
  
  <p>I want to have only diagonal area shown by green line. What should I do?</p>