title: How to draw a complex transparent circle on Google Maps API
body: <p>Recently I got a task that is to draw circles on my own website with Google Maps API.
  The complexity is the center of the circle is representing a "signal transmitter" and I need to make the circle transparent, with the opacity of each pixel reprseting the signal intensity of the exact location.</p>
  
  <p>My basic idea is to extend the "Overlay" of Google Map API, so I have to write it in javascript I think.</p>
  
  <p>The key part is to draw a circle with gradually changing opacity (inner stronger, outter lighter) and idealy, I can specify the opacity of each pixel.</p>
  
  <p>I've been looking for approaches like CSS3, SVG, VML and even jquery and AJAX but still having no idea about how to archve this.</p>
  
  <p>Thank you very much for your helping!</p>