javascript 如何使用leaflet.draw从多边形中获取区域字符串
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How to get the area string from a polygon using leaflet.draw
提问by Marty.H
I am trying to get the area measurements of polygons so I can list them in a table to the side of the map, next to the name of the polygon. This is what I have tried with no success:
我正在尝试获取多边形的面积测量值，以便我可以将它们列在地图一侧的表格中，在多边形名称旁边。这是我尝试过但没有成功的方法：
$("#polygon").on("click", function (){
createPolygon = new L.Draw.Polygon(map, drawControl.options.polygon);
createPolygon.enable();
}
var polygon = new L.featureGroup();
map.on('draw:created', function (e) {
var type = e.layerType,
layer = e.layer;
if (type === 'polygon') {
polygons.addLayer(layer);
}
var seeArea = createPolygon._getMeasurementString();
console.log(seeArea); //Returns null
}
Any help on this would be appreciated!
对此的任何帮助将不胜感激！
回答by The Brofessor
You can access the geometry utility library provided with Leaflet.
您可以访问 Leaflet 提供的几何实用程序库。
var area = L.GeometryUtil.geodesicArea(layer.getLatLngs());
In your example, you are trying to access a control itself, which is what the variable createPolygon is assigned to. Instead, you want to take the area of the layer that got drawn.
在您的示例中，您试图访问控件本身，这是变量 createPolygon 分配给的内容。相反，您想要获取绘制的图层区域。
map.on('draw:created', function (e) {
var type = e.layerType,
layer = e.layer;
if (type === 'polygon') {
polygons.addLayer(layer);
var seeArea = L.GeometryUtil.geodesicArea(layer.getLatLngs());
console.log(seeArea);
}
}
Once you verify you are getting the area, you can just assign it to the variables that populate the table next to the map.
一旦您确认您正在获取该区域，您就可以将其分配给填充地图旁边表格的变量。
Note: area will be in squareMeters by default
注意：默认情况下面积以平方米为单位
回答by Facundo Ferrari
Hello add corrections:
你好补充更正：
var seeArea = L.GeometryUtil.geodesicArea(layer.getLatLngs()[0]); console.log(seeArea);
var seeArea = L.GeometryUtil.geodesicArea(layer.getLatLngs()[0]); 控制台日志（见区域）；
回答by lauren.marietta
I found that none of the above answers worked for calculating the area of non-contiguouspolygons. Here's an example polygon where the above functions returned an area of 0:
我发现上述答案都不适用于计算非连续多边形的面积。这是一个示例多边形，其中上述函数返回的面积为 0：
For anyone who needs to do that, here is the code that worked for me (using the L.GeometryUtilfunction from Leaflet.draw):
对于需要这样做的任何人，以下是对我L.GeometryUtil有用的代码（使用Leaflet.draw 中的函数）：
var poly = // Your polygon layer here; may or may not be contiguous
var area = 0;
for (island of poly.getLatLngs()) {
// If the polygon is non-contiguous, access the island
if (island.length < 2) {
island = island[0]
}
// Sum the area within each "island"
area += L.GeometryUtil.geodesicArea(island);
}回答by KuN
L.GeometryUtil.geodesicArea(layer.getLatLngs()[0]should get you the area.
L.GeometryUtil.geodesicArea(layer.getLatLngs()[0]应该让你的区域。
But I ended up using leaflet-geoman-freeto do the drawing and use turf.jsto get the area.
但是我最终使用leaflet-geoman-free来绘制并使用turf.js来获取该区域。
map.pm.enableDraw('Polygon', {
snappable: true,
snapDistance: 20,
});
map.on('pm:create', e => {
const layer = e.layer
alert(turf.area(layer.toGeoJSON()))
});
