Google maps 如何在我'；你把它添加到地图上了吗？

我基本上想到的是谷歌在这个例子中所做的事情

每一秒，我都想在特定的坐标处添加圆，然后慢慢地将它们淡出。我已经设法在地图上添加了圆圈：

var citymap = {};
citymap['chicago'] = {
  center: new google.maps.LatLng(41.878113, -87.629798),
  population: 100
};
citymap['amsterdam'] = {
  center: new google.maps.LatLng(52.878113, 5.629798),
  population: 40
};
citymap['paris'] = {
  center: new google.maps.LatLng(48.9021449, 2.4699208),
  population: 100
};
citymap['moscow'] = {
  center: new google.maps.LatLng(56.021369, 37.9650909),
  population: 100
};
citymap['newyork'] = {
  center: new google.maps.LatLng(40.9152414, -73.70027209999999),
  population: 80
};
citymap['losangeles'] = {
  center: new google.maps.LatLng(34.3373061, -118.1552891),
  population: 65
}

for (var city in citymap) {
    var populationOptions = {
        strokeColor: "#900057",
        strokeOpacity: 1,
        strokeWeight: 1,
        fillColor: "#900057",
        fillOpacity: 0.35,
        map: map,
        clickable: false,
        center: citymap[city].center,
        radius: citymap[city].population * 2000
    };
    cityCircle = new google.maps.Circle(populationOptions);
}

---

但我找不到如何在任何地方淡出它们。已经试过浏览Google Maps API文档，甚至示例代码，但可能我遗漏了一些内容。

要淡出它们，需要降低填充和笔划的不透明度，直到其为0.0

setInterval(fadeCityCircles,1000);

function fadeCityCircles() {
  for (var city in citymap) {
    var fillOpacity = citymap[city].cityCircle.get("fillOpacity");
    fillOpacity -= 0.02;
    if (fillOpacity < 0) fillOpacity =0.0;
    var strokeOpacity = citymap[city].cityCircle.get("strokeOpacity");
    strokeOpacity -= 0.05;
    if (strokeOpacity < 0) strokeOpacity =0.0;
    citymap[city].cityCircle.setOptions({fillOpacity:fillOpacity, strokeOpacity:strokeOpacity});
  }
}  

setInterval（fadeCityCircles，1000）；
函数fadeCityCircles（）{
用于（城市地图中的var城市）{
var fillOpacity=citymap[city].cityCircle.get（“fillOpacity”）；
填充不透明度-=0.02；
如果（fillOpacity<0）fillOpacity=0.0；
var strokeOpacity=citymap[city].cityCircle.get（“strokeOpacity”）；
冲程不透明度-=0.05；
如果（strokeOpacity<0）strokeOpacity=0.0；
citymap[city].cityCircle.setOptions（{fillOpacity:fillOpacity，strokeOpacity:strokeOpacity}）；
}
}  

---

要淡出它们，需要降低填充和笔划的不透明度，直到其为0.0

setInterval(fadeCityCircles,1000);

function fadeCityCircles() {
  for (var city in citymap) {
    var fillOpacity = citymap[city].cityCircle.get("fillOpacity");
    fillOpacity -= 0.02;
    if (fillOpacity < 0) fillOpacity =0.0;
    var strokeOpacity = citymap[city].cityCircle.get("strokeOpacity");
    strokeOpacity -= 0.05;
    if (strokeOpacity < 0) strokeOpacity =0.0;
    citymap[city].cityCircle.setOptions({fillOpacity:fillOpacity, strokeOpacity:strokeOpacity});
  }
}  

setInterval（fadeCityCircles，1000）；
函数fadeCityCircles（）{
用于（城市地图中的var城市）{
var fillOpacity=citymap[city].cityCircle.get（“fillOpacity”）；
填充不透明度-=0.02；
如果（fillOpacity<0）fillOpacity=0.0；
var strokeOpacity=citymap[city].cityCircle.get（“strokeOpacity”）；
冲程不透明度-=0.05；
如果（strokeOpacity<0）strokeOpacity=0.0；
citymap[city].cityCircle.setOptions（{fillOpacity:fillOpacity，strokeOpacity:strokeOpacity}）；
}
}