arcgis for js如何画台风风圈

function getAirRing(c, center, index) {//风圈;level风力级数，center原点
    var arColor;
    switch (c.level) {
        case 7: arColor = [83, 168, 113]; break;//7级风圈
        case 10: arColor = [175, 192, 130]; break;
        case 12: arColor = [185, 121, 96]; break;
        default: arColor = [83, 168, 113]; break;
    }

    //算出所有的点
    var points = new Array();
    getPoints(center, c.EN, 0);//东北方向
    getPoints(center, c.ES, 90);
    getPoints(center, c.WS, 180);
    getPoints(center, c.WN, 270);
    points[points.length] = points[0];//首尾连接

    //设置填充symbol
    var bColor = arColor; bColor.push(0.5);//透明度
    var sfl = new esri.symbol.SimpleFillSymbol(
        esri.symbol.SimpleFillSymbol.STYLE_SOLID,
        new esri.symbol.SimpleLineSymbol(
            esri.symbol.SimpleLineSymbol.STYLE_SOLID,
            new dojo.Color(arColor),
            2
        ),
        new dojo.Color(bColor)
    );

    //将点连成多边形
    var polygon = new esri.geometry.Polygon(points);
    //并填充，还附带上各种风圈数据
    var gr = new esri.Graphic(polygon, sfl,
        {
            "level": c.level, "wn": c.WN, "en": c.EN, "es": c.ES, "ws": c.WS,
            "attrtype": "airRing", "index": index,
        },
        new esri.InfoTemplate("风圈:${level}", tplAirRing));
    return gr;

    //此方法照抄来的，1度1个点
    function getPoints(center, cradius, startAngle) {
        var radius = cradius / 100; 
        var pointNum = 90;
        var endAngle = startAngle + 90;

        var sin;
        var cos;
        var x;
        var y;
        var angle;

        for (var i = 0; i <= pointNum; i++) {
            angle = startAngle + (endAngle - startAngle) * i
                / pointNum;
            sin = Math.sin(angle * Math.PI / 180);
            cos = Math.cos(angle * Math.PI / 180);
            x = center[0] + radius * sin;
            y = center[1] + radius * cos;
            points.push([x, y]);
        }
    }
}