上一篇介绍了使用leaflet绘制圆形，那如何计算圆形的面积呢？
1、使用数学公式计算，绘制好圆形后，获取中心点以及半径即可
2、使用第三方工具计算，如turf.js. 这里turf的area方法入参为geojson对象
3、使用超图的地图服务做面积计算，见下文范例
<!DOCTYPE html>
<html> <head>
<meta charset="UTF-8">
<title>图形绘制并计算面积</title>
</head> <body style=" margin: 0;overflow: hidden;background: #fff;width: 100%;height:100%;position: absolute;top: 0;">
<div id="map" style="width: 100%;height:100%"></div>
<script type="text/javascript" include="turf,leaflet.draw" src="../../dist/include-leaflet.js"></script> <script type="text/javascript">
var map, url = "http://support.supermap.com.cn:8090/iserver/services/map-china400/rest/maps/China";
map = L.map('map', {
center: [33, 114],
zoom: 4
});
L.supermap.tiledMapLayer(url).addTo(map); var editableLayers = new L.FeatureGroup();
map.addLayer(editableLayers); var drawControl = new L.Control.Draw({
position: 'topleft',
draw: {
polyline: false,
polygon: false,
circle: {},
rectangle: false,
marker: false,
remove: true
},
edit: {
featureGroup: editableLayers,
remove: true
}
});
map.addControl(drawControl);
handleMapEvent(drawControl._container, map); map.on(L.Draw.Event.CREATED, function (e) {
var type = e.layerType,
layer = e.layer;
if (type === 'marker') {
layer.bindPopup('A popup!');
}
editableLayers.addLayer(layer); //绘制完成后，获取圆形的半径和中心点坐标
var radius = layer._mRadius;
var lonlat = layer._latlng;
console.log(radius + "; " + lonlat); //点集
var parts = [];
//计算圆的边缘所有点
for (var i = 0; i < 360; i++) {
var radians = (i + 1) * Math.PI / 180;
var circlePoint = [Math.cos(radians) * radius + lonlat.lat, Math.sin(radians) * radius + lonlat
.lng
];
parts[i] = circlePoint;
}
//用点集来构造leaflet的面对象
var polygon1 = L.polygon(parts); //服务端计算面积
//getAreaByServer(polygon1);
//数学公式计算面积
//getAreaByClient(radius);
//turf计算面积
getAreaByTurf(polygon1.toGeoJSON());
}); function getAreaByClient(radius) {
//使用数学公式或者用turf计算
var square = radius * radius * Math.PI;
alert("面积： " + square + " 平方米");
} function getAreaByTurf(polygon) {
var area = turf.area(polygon);
alert("面积： " + area + " 平方米");
} function getAreaByServer(polygon) {
//参数说明： SuperMap.MeasureParameters(geometry, options)
// distanceMode(指定量算的方式为按球面长度 'Geodesic' 或者平面长度 'Planar' 来计算，默认是球面)
// prjCoordSys（指定该量算操作所使用的投影）
// unit (量算单位。默认量算结果以米为单位)
var areaMeasureParam = new SuperMap.MeasureParameters(polygon, { distanceMode: 'Geodesic' });
L.supermap
.measureService(url)
.measureArea(areaMeasureParam, function (serviceResult) {
alert("面积： " + serviceResult.result.area + " 平方米");
});
} function handleMapEvent(div, map) {
if (!div || !map) {
return;
}
div.addEventListener('mouseover', function () {
map.scrollWheelZoom.disable();
map.doubleClickZoom.disable();
});
div.addEventListener('mouseout', function () {
map.scrollWheelZoom.enable();
map.doubleClickZoom.enable();
});
}
</script>
</body> </html>
