Leaflet地图 — 绘制台风风圈

Leaflet -- 绘制台风风圈

实现效果
实现思路
核心代码
全部代码
结束语

实现效果

台风风圈实现效果

实现思路

我们先来看一下，后端返回的数据格式。下面是台风轨迹列表中的一条记录，红框的字段就是画台风风圈的关键字段：se、se、ne、nw分别代表当前点位台风风圈的东南、西南、东北、西北四个方向的影响半径。
台风轨迹列表点位数据详情
html的图形的绘制，svg和canvas。最开始选择的是canvas，绘制好了之后，在地图的位移时要重新计算和绘制实现效果不理想。
在这里插入图片描述

之后看了下leaflet的源码发现L.Polygon 是继承自L.Path对象。而L.Path本身又是，基于SVG实现的。那就好办了，我们继承L.Polygon再写个类L.Typhoon
在这里插入图片描述
L.Typhoon类中，两个最核心方法：一个是计算风圈四个方向半径，一个是绘制台风风圈：基于SVG的path元素来实现的，下面是代码：

核心代码

计算风圈半径：台风中心经纬度和半径计算屏幕坐标

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projectLatlngs: function () {
try {
var e = this._latlng;
this._point = this._map.latLngToLayerPoint(e);
var t_northeast = this._getLngRadius(this._getLatRadius(this._circle.ne * 1000)),
i_northeast = this._map.latLngToLayerPoint([e.lat, e.lng - t_northeast]);
this._radius_northeast = Math.max(this._point.x - i_northeast.x, 1);
var t_southeast = this._getLngRadius(this._getLatRadius(this._circle.se * 1000)),
i_southeast = this._map.latLngToLayerPoint([e.lat, e.lng - t_southeast]);
this._radius_southeast = Math.max(this._point.x - i_southeast.x, 1);
var t_southwest = this._getLngRadius(this._getLatRadius(this._circle.sw * 1000)),
i_southwest = this._map.latLngToLayerPoint([e.lat, e.lng - t_southwest]);
this._radius_southwest = Math.max(this._point.x - i_southwest.x, 1);
var t_northwest = this._getLngRadius(this._getLatRadius(this._circle.nw * 1000)),
i_northwest = this._map.latLngToLayerPoint([e.lat, e.lng - t_northwest]);
this._radius_northwest = Math.max(this._point.x - i_northwest.x, 1)
} catch (e) {
this._radius_northeast = null;
this._radius_southeast = null;
this._radius_southwest = null;
this._radius_northwest = null
}
},

绘制台风风圈：

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getTyphoonPath: function () {
if (this._radius_northeast && this._radius_southeast && this._radius_southwest && this._radius_northwest) {
var t = this._point;
var e_northeast = this._radius_northeast;
var path_svg = "M" + t.x + "," + (t.y - e_northeast);
var path_vml = "M" + t.x + "," + (t.y - e_northeast);
path_svg += "A" + e_northeast + "," + e_northeast + ",0,0,1," + (t.x + e_northeast) + "," + t.y;
path_vml += " ae " + t.x + "," + t.y + " " + e_northeast + "," + e_northeast + " " + 65535 * 450 + "," + -5898150;
var e_southeast = this._radius_southeast;
path_svg += "L" + (t.x + e_southeast) + "," + t.y;
path_svg += "A" + e_southeast + "," + e_southeast + ",0,0,1," + t.x + "," + (t.y + e_southeast);
path_vml += " ae " + t.x + "," + t.y + " " + e_southeast + "," + e_southeast + " " + 65535 * 360 + "," + -5898150;
var e_southwest = this._radius_southwest;
path_svg += "L" + t.x + "," + (t.y + e_southwest);
path_svg += "A" + e_southwest + "," + e_southwest + ",0,0,1," + (t.x - e_southwest) + "," + t.y;
path_vml += " ae " + t.x + "," + t.y + " " + e_southwest + "," + e_southwest + " " + 65535 * 270 + "," + -5898150;
var e_northwest = this._radius_northwest;
path_svg += "L" + (t.x - e_northwest) + "," + t.y;
path_svg += "A" + e_northwest + "," + e_northwest + ",0,0,1," + t.x + "," + (t.y - e_northwest) + "z";
path_vml += " ae " + t.x + "," + t.y + " " + e_northwest + "," + e_northwest + " " + 65535 * 180 + "," + -5898150 + "X";
this.svgPath = L.Browser.svg ? path_svg : path_vml
return L.Browser.svg ? path_svg : path_vml
}
return ""
},

全部代码

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结束语

以上就是台风风圈的绘制实现及代码。本文是基于leaflet v1.6.0的完成的，低版本的leaflet是否可以用并未进行测试，请自行进行测试或对代码进行修改。