# How to draw typhoon wind circle in arcgis for js

In arcgis for js, it is not difficult to draw a circle. Small ones can use SimpleMarkerSymbol, "style": "esriSMSCircle";
If it's big, just a new Circle

But what if it's something like a typhoon? It looks like a circle but not a circle. How to draw?
The answer is to draw polygons. The wind circle shown in the figure is exactly three polygons. In fact, the so-called circle is not the result of infinite approximation of polygons? It's like calculus says that?

The principle of drawing typhoon wind circle is as follows: take the center of the circle as the origin, take the true north direction as 0 degree, draw points clockwise, 1 degree as 1 point, and connect them into a line, and finally return to the true north direction to form a closed polygon; then fill it. The radius of typhoon can be divided into four directions: Northeast, Southeast, southwest and northwest. The distance from each direction to the center of the circle may be different, so there are four zigzag wind circles.

The code is as follows:

```function getAirRing(c, center, index) {//Wind circle; level wind series, center origin
var arColor;
switch (c.level) {
case 7: arColor = [83, 168, 113]; break;//7-Stage wind ring
case 10: arColor = [175, 192, 130]; break;
case 12: arColor = [185, 121, 96]; break;
default: arColor = [83, 168, 113]; break;
}

//Work out all the points
var points = new Array();
getPoints(center, c.EN, 0);//Northeast
getPoints(center, c.ES, 90);
getPoints(center, c.WS, 180);
getPoints(center, c.WN, 270);
points[points.length] = points;//Head tail connection

//Set fill symbol
var bColor = arColor; bColor.push(0.5);//transparency
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)
);

//Polygon points
var polygon = new esri.geometry.Polygon(points);
//And fill it with various wind circle data
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("Wind coil:\${level}", tplAirRing));
return gr;

//It's copied by this method, 1 degree and 1 point
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 + radius * sin;
y = center + radius * cos;
points.push([x, y]);
}
}
}```

Posted by polywog on Thu, 30 Apr 2020 21:17:26 -0700