arcgis for js如何画台风风圈
转自:https://blog.csdn.net/leftfist/article/details/78984533#commentBox
arcgis for js里面,画一个圆不是什么难事。小的可以用SimpleMarkerSymbol
,"style": "esriSMSCircle"
;
大的话,直接就来一个new Circle
但是,如果是类似台风风圈这类的呢?
似圆非圆,该咋画?
答案是画多边形。如图所示的风圈,正是3个多边形。其实所谓的圆,不就是多边形无限逼近的结果吗?好像微积分里有说到这个?
画台风风圈的原理如下:以圆心为原点,以正北方向为0度,顺时针画点,1度为1个点,并连成线,并最终回到正北方向,形成封闭的多边形;然后再加以填充。由于台风半径分为东北、东南、西南、西北四个方向,每个方向距离圆心可能长度不一,于是就形成了有四个锯齿状的风圈。
代码如下:
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]); } } }