Draw ring (not circle) in Google Maps API

Question

I would like to draw a ring 20km thick with empty 5km circle inside. I dont how how to do it. I believe it is possible.

One simple solution could be to substract one

Answer 1

Create a drawCircle function:

function drawCircle(point, radius, dir) { 
var d2r = Math.PI / 180;   // degrees to radians 
var r2d = 180 / Math.PI;   // radians to degrees 
var earthsradius = 3963; // 3963 is the radius of the earth in miles

   var points = 32; 

   // find the raidus in lat/lon 
   var rlat = (radius / earthsradius) * r2d; 
   var rlng = rlat / Math.cos(point.lat() * d2r); 


   var extp = new Array(); 
   if (dir==1)  {var start=0;var end=points+1} // one extra here makes sure we connect the
   else     {var start=points+1;var end=0}
   for (var i=start; (dir==1 ? i < end : i > end); i=i+dir)  
   { 
      var theta = Math.PI * (i / (points/2)); 
      ey = point.lng() + (rlng * Math.cos(theta)); // center a + radius x * cos(theta) 
      ex = point.lat() + (rlat * Math.sin(theta)); // center b + radius y * sin(theta) 
      extp.push(new google.maps.LatLng(ex, ey)); 
      bounds.extend(extp[extp.length-1]);
   } 
   // alert(extp.length);
   return extp;
   }

Then you can use it like this:

  var donut = new google.maps.Polygon({
                 paths: [drawCircle(new google.maps.LatLng(-33.9,151.2), 100, 1),
                         drawCircle(new google.maps.LatLng(-33.9,151.2), 50, -1)],
                 strokeColor: "#0000FF",
                 strokeOpacity: 0.8,
                 strokeWeight: 2,
                 fillColor: "#FF0000",
                 fillOpacity: 0.35
     });
     donut.setMap(map);

Note that the inner circle needs to "wind" opposite the outer circle.

Example (as posted by Dr Molle)

code snippet:

function drawCircle(point, radius, dir) {
  var d2r = Math.PI / 180; // degrees to radians 
  var r2d = 180 / Math.PI; // radians to degrees 
  var earthsradius = 3963; // 3963 is the radius of the earth in miles

  var points = 32;

  // find the raidus in lat/lon 
  var rlat = (radius / earthsradius) * r2d;
  var rlng = rlat / Math.cos(point.lat() * d2r);


  var extp = new Array();
  if (dir == 1) {
    var start = 0;
    var end = points + 1
  } // one extra here makes sure we connect the
  else {
    var start = points + 1;
    var end = 0
  }
  for (var i = start;
    (dir == 1 ? i < end : i > end); i = i + dir) {
    var theta = Math.PI * (i / (points / 2));
    ey = point.lng() + (rlng * Math.cos(theta)); // center a + radius x * cos(theta) 
    ex = point.lat() + (rlat * Math.sin(theta)); // center b + radius y * sin(theta) 
    extp.push(new google.maps.LatLng(ex, ey));
    bounds.extend(extp[extp.length - 1]);
  }
  // alert(extp.length);
  return extp;
}

var map = null;
var bounds = null;

function initialize() {
  var myOptions = {
    zoom: 10,
    center: new google.maps.LatLng(-33.9, 151.2),
    mapTypeControl: true,
    mapTypeControlOptions: {
      style: google.maps.MapTypeControlStyle.DROPDOWN_MENU
    },
    navigationControl: true,
    mapTypeId: google.maps.MapTypeId.ROADMAP
  }
  map = new google.maps.Map(document.getElementById("map_canvas"),
    myOptions);

  bounds = new google.maps.LatLngBounds();

  var donut = new google.maps.Polygon({
    paths: [drawCircle(new google.maps.LatLng(-33.9, 151.2), 100, 1),
      drawCircle(new google.maps.LatLng(-33.9, 151.2), 50, -1)
    ],
    strokeColor: "#0000FF",
    strokeOpacity: 0.8,
    strokeWeight: 2,
    fillColor: "#FF0000",
    fillOpacity: 0.35
  });
  donut.setMap(map);

  map.fitBounds(bounds);

}
google.maps.event.addDomListener(window, "load", initialize);

html,
body,
#map_canvas {
  height: 100%;
  width: 100%;
  margin: 0px;
  padding: 0px
}