js版根据经纬度计算多边形面积（墨卡托投影）

[摘要：var earthRadiusMeters = 6371000.0; var metersPerDegree = 2.0 * Math.PI * earthRadiusMeters / 360.0; var radiansPerDegree = Math.PI / 180.0; var degr]

var earthRadiusMeters = 6371000.0;var metersPerDegree = 2.0 * Math.PI * earthRadiusMeters / 360.0;var radiansPerDegree = Math.PI / 180.0;var degreesPerRadian = 180.0 / Math.PI;var pointArr;$(document).ready(function() {pointArr = new Array();b();});function calculateArea(points) {if (points.length > 2) {var areaMeters2 = PlanarPolygonAreaMeters2(points);if (areaMeters2 > 1000000.0) {areaMeters2 = SphericalPolygonAreaMeters2(points);alert("面积为" + areaMeters2 + "平方米");}}}/*球面多边形面积计算*/function SphericalPolygonAreaMeters2(points) {var totalAngle = 0;for (var i = 0; i < points.length; i++) {var j = (i + 1) % points.length;var k = (i + 2) % points.length;totalAngle += Angle(points[i], points[j], points[k]);}var planarTotalAngle = (points.length - 2) * 180.0;var sphericalExcess = totalAngle - planarTotalAngle;if (sphericalExcess > 420.0) {totalAngle = points.length * 360.0 - totalAngle;sphericalExcess = totalAngle - planarTotalAngle;} else if (sphericalExcess > 300.0 && sphericalExcess < 420.0) {sphericalExcess = Math.abs(360.0 - sphericalExcess);}return sphericalExcess * radiansPerDegree * earthRadiusMeters * earthRadiusMeters;}/*角度*/function Angle(p1, p2, p3) {var bearing21 = Bearing(p2, p1);var bearing23 = Bearing(p2, p3);var angle = bearing21 - bearing23;if (angle < 0) {angle += 360;}return angle;}/*方向*/function Bearing(from, to) {var lat1 = from[1] * radiansPerDegree;var lon1 = from[0] * radiansPerDegree;var lat2 = to[1] * radiansPerDegree;var lon2 = to[0] * radiansPerDegree;var angle = -Math.atan2(Math.sin(lon1 - lon2) * Math.cos(lat2), Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) * Math.cos(lat2) * Math.cos(lon1 - lon2));if (angle < 0) {angle += Math.PI * 2.0;}angle = angle * degreesPerRadian;return angle;}/*平面多边形面积*/function PlanarPolygonAreaMeters2(points) {var a = 0;for (var i = 0; i < points.length; ++i) {var j = (i + 1) % points.length;var xi = points[i][0] * metersPerDegree * Math.cos(points[i][1] * radiansPerDegree);var yi = points[i][1] * metersPerDegree;var xj = points[j][0] * metersPerDegree * Math.cos(points[j][1] * radiansPerDegree);var yj = points[j][1] * metersPerDegree;a += xi * yj - xj * yi;}return Math.abs(a / 2);}function b() {var s = "112.523197631836,37.868892669677734;112.5170669555664,37.8605842590332;112.52099609375,37.849857330322266;112.54137420654297,37.8512732521875;112.5351180302734,37.858699798583984";var s1 = new Array()s1 = s.split(";");for (var i = 0; i < s1.length; i++) {var ss = s1[i];var temp = ss.split(",");var point = new Array();point.push(Number(temp[0]), Number(temp[1]));pointArr.push(point);}calculateArea(pointArr);}