百度地图中多边形覆盖物的面积计算

来源：互联网发布：系统数据保密协议编辑：程序博客网时间：2024/06/06 04:32

面积计算原理

参考古人的定理：球面多边形计算面积的关键在于计算多边形所有角的度数，对于球面N变形，所有角的和为S,球的半径为R，面积计算公式：
$(S - (N - 2) * P i) * R * R$

直接在地图上显示一个多边形覆盖物：

<html><head><title></title><meta http-equiv="content-type" content="text/html; charset=UTF-8"></head><script type="text/javascript" src="http://api.map.baidu.com/api?v=2.0&ak=秘钥"></script><body>  <div id="allmap" style="width:100%;height:100%"></div>  <script type="text/javascript">    var map = new BMap.Map("allmap");    map.centerAndZoom(new BMap.Point(121.329178,31.184047), 14);    map.enableScrollWheelZoom();        //添加固定范围        var polygon = new BMap.Polygon([        new BMap.Point(121.309056,31.22383),        new BMap.Point(121.309918,31.207647),        new BMap.Point(121.322998,31.185036),        new BMap.Point(121.331046,31.171689),        new BMap.Point(121.331621,31.170082),        new BMap.Point(121.353324,31.177868),        new BMap.Point(121.363673,31.187755),        new BMap.Point(121.35548,31.229018),        new BMap.Point(121.335646,31.229141),        new BMap.Point(121.317967,31.224201)        ], {strokeColor:"red", strokeWeight:2, strokeOpacity:0.8});  //创建多边形        map.addOverlay(polygon);   //增加多边形    </script></body></html>

计算面积逻辑代码如下：：

      //参数是一个百度类型的多边形覆盖物      function getArea(polygon){        // 检查类型：既不是百度类型的范围又不是数组类型的数据，直接返回0        if (!(polygon instanceof BMap.Polygon) && !(polygon instanceof Array)) {                return 0;        }         //如果是百度类型的，得到点集合，不是的话，另说。         var pts = new Array();         if (polygon instanceof BMap.Polygon) {              pts = polygon.getPath();         }         //判断数组的长度，如果是小于3的话，不构成面，无法计算面积         if (pts.length < 3) {                return 0;         }         var totalArea = 0;// 初始化总面积         var LowX = 0.0;          var LowY = 0.0;          var MiddleX = 0.0;         var MiddleY = 0.0;         var HighX = 0.0;         var HighY = 0.0;         var AM = 0.0;         var BM = 0.0;         var CM = 0.0;         var AL = 0.0;         var BL = 0.0;         var CL = 0.0;         var AH = 0.0;         var BH = 0.0;         var CH = 0.0;         var CoefficientL = 0.0;         var CoefficientH = 0.0;         var ALtangent = 0.0;         var BLtangent = 0.0;         var CLtangent = 0.0;         var AHtangent = 0.0;         var BHtangent = 0.0;         var CHtangent = 0.0;         var ANormalLine = 0.0;         var BNormalLine = 0.0;         var CNormalLine = 0.0;         var OrientationValue = 0.0;         var AngleCos = 0.0;         var Sum1 = 0.0;         var Sum2 = 0.0;         var Count2 = 0;         var Count1 = 0;         var Sum = 0.0;         var Radius = 6378137.0;// ,WGS84椭球半径         var Count = pts.length;          for ( var i = 0; i < Count; i++) {                if (i == 0) {                    LowX = pts[Count - 1].lng * Math.PI / 180;                    LowY = pts[Count - 1].lat * Math.PI / 180;                    MiddleX = pts[0].lng * Math.PI / 180;                    MiddleY = pts[0].lat * Math.PI / 180;                    HighX = pts[1].lng * Math.PI / 180;                    HighY = pts[1].lat * Math.PI / 180;                } else if (i == Count - 1) {                    LowX = pts[Count - 2].lng * Math.PI / 180;                    LowY = pts[Count - 2].lat * Math.PI / 180;                    MiddleX = pts[Count - 1].lng * Math.PI / 180;                    MiddleY = pts[Count - 1].lat * Math.PI / 180;                    HighX = pts[0].lng * Math.PI / 180;                    HighY = pts[0].lat * Math.PI / 180;                } else {                    LowX = pts[i - 1].lng * Math.PI / 180;                    LowY = pts[i - 1].lat * Math.PI / 180;                    MiddleX = pts[i].lng * Math.PI / 180;                    MiddleY = pts[i].lat * Math.PI / 180;                    HighX = pts[i + 1].lng * Math.PI / 180;                    HighY = pts[i + 1].lat * Math.PI / 180;                }                AM = Math.cos(MiddleY) * Math.cos(MiddleX);                BM = Math.cos(MiddleY) * Math.sin(MiddleX);                CM = Math.sin(MiddleY);                AL = Math.cos(LowY) * Math.cos(LowX);                BL = Math.cos(LowY) * Math.sin(LowX);                CL = Math.sin(LowY);                AH = Math.cos(HighY) * Math.cos(HighX);                BH = Math.cos(HighY) * Math.sin(HighX);                CH = Math.sin(HighY);                CoefficientL = (AM * AM + BM * BM + CM * CM)/ (AM * AL + BM * BL + CM * CL);                CoefficientH = (AM * AM + BM * BM + CM * CM)/ (AM * AH + BM * BH + CM * CH);                ALtangent = CoefficientL * AL - AM;                BLtangent = CoefficientL * BL - BM;                CLtangent = CoefficientL * CL - CM;                AHtangent = CoefficientH * AH - AM;                BHtangent = CoefficientH * BH - BM;                CHtangent = CoefficientH * CH - CM;                AngleCos = (AHtangent * ALtangent + BHtangent * BLtangent + CHtangent* CLtangent)/ (Math.sqrt(AHtangent * AHtangent + BHtangent* BHtangent + CHtangent * CHtangent) * Math.sqrt(ALtangent * ALtangent + BLtangent* BLtangent + CLtangent * CLtangent));                AngleCos = Math.acos(AngleCos);                ANormalLine = BHtangent * CLtangent - CHtangent * BLtangent;                BNormalLine = 0 - (AHtangent * CLtangent - CHtangent* ALtangent);                CNormalLine = AHtangent * BLtangent - BHtangent * ALtangent;                if (AM != 0)                    OrientationValue = ANormalLine / AM;                else if (BM != 0)                    OrientationValue = BNormalLine / BM;                else                    OrientationValue = CNormalLine / CM;                if (OrientationValue > 0) {                    Sum1 += AngleCos;                    Count1++;                } else {                    Sum2 += AngleCos;                    Count2++;                }            }            var tempSum1, tempSum2;            tempSum1 = Sum1 + (2 * Math.PI * Count2 - Sum2);            tempSum2 = (2 * Math.PI * Count1 - Sum1) + Sum2;            if (Sum1 > Sum2) {                if ((tempSum1 - (Count - 2) * Math.PI) < 1)                    Sum = tempSum1;                else                    Sum = tempSum2;            } else {                if ((tempSum2 - (Count - 2) * Math.PI) < 1)                    Sum = tempSum2;                else                    Sum = tempSum1;            }            totalArea = (Sum - (Count - 2) * Math.PI) * Radius * Radius;            return totalArea; // 返回总面积}

调用计算面积的方法：

      //1秒后弹出面积值，单位:米       setTimeout(function(){        alert(getArea(polygon));       },1000);

如图所示：
这里写图片描述

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