title: using HTML5 Canvas - rotate image about arbitrary point
body: <p>Rotate the dial on top of a semi circular(Northern Hemisphere) image as background.
  range could be 0 - 180 degrees.
  on input to the method that does canvas transformation, the dial would rotate and stop over the matched value.
  Here's what I was trying based on help and sample passed on by <a href="https://stackoverflow.com/users/405017/phrogz" title="phrogz ">phrogz </a></p>