GIS面积距离计算

1. 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);  }