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百度地图中多边形覆盖物的面积计算

2016-06-14 09:37 561 查看

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)∗Pi)∗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：

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标签：  百度地图
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