连续经纬度点求面积

path=[{lat:x,lng:y}]

computeSignedArea(path)

function computeSignedArea(path) {

//传入path：{

let radius = 6371009

let len = path.length;

if (len < 3) return 0;

let total = 0;

let prev = path[len - 1];

let prevTanLat = Math.tan(((Math.PI / 2 - prev.lat / 180 * Math.PI) / 2));

let prevLng = (prev.lng) / 180 * Math.PI;

for (let i in path) {

let tanLat = Math.tan((Math.PI / 2 -

(path[i].lat) / 180 * Math.PI) / 2);

let lng = (path[i].lng) / 180 * Math.PI;

total += polarTriangleArea(tanLat, lng, prevTanLat, prevLng);

prevTanLat = tanLat;

prevLng = lng;

}

return Math.abs(total * (radius * radius));

}

function polarTriangleArea(tan1, lng1, tan2, lng2) {

let deltaLng = lng1 - lng2;

let t = tan1 * tan2;

return 2 * Math.atan2(t * Math.sin(deltaLng), 1 + t * Math.cos(deltaLng));

}