title: How to calculate which grid squares a circle touches?
body: <p>I have an image consisting from roughly 4,000,000 pixels. Each pixel has a geographic XY-coordinate (the coordinate is located in the center of the pixel) and each pixel corresponds to a A x A meter square. </p>
  
  <p>Lets say I drop a random point on to the image (with random XY-coordinates) and draw a circle of radius B meters around this point: </p>
  
  <p><a href="https://i.stack.imgur.com/pDpaK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pDpaK.png" alt="enter image description here"></a></p>
  
  <p>My question is: How  can I efficiently calculate which squares the circle touches? </p>