title: stacking multiple images with transparency one above another on iPhone iOS
body: <p>I'm writing a compass that should rotate a compass image according to <code>CLLocation</code> course. </p>
  
  <p>On top of that compass I'd like to display an arrow that should point into a different  direction than the compass does. To achieve that I thought I could stack multiple images one upon the other and have them rotate independently. <strong>The arrow image should be transparent.</strong></p>
  
  <p><strong>How do I stack these images and rotate them independently?</strong></p>