Question

我有一个来自谷歌地图的“地方”对象，它有一组坐标，代表一个给定位置的边界框，比如伦敦。每组坐标都有纬度和经度。

我写了下面的代码来找到中心点，但我不确定它是否确实产生了中心点。如果多边形有5个点而不是4个怎么办？此外，这可以通过更少的操作以更有效的方式完成吗？

function average(array) {
  // Add together and then divide by the length
  return _.reduce(array, function (sum, num) {
    return sum + num;
  }, 0) / array.length;
}

// I have a two-dimensional array that I want to get the average of

var coords = [
  [ -1.2, 5.1 ],
  [ -1.3, 5.2 ],
  [ -1.8, 5.9 ],
  [ -1.9, 5.8 ]
]

// So I get the first column

var lats = coords.map(function (coord) {
  return coord[0];
})

// Then the second

var longs = coords.map(function (coord) {
  return coord[1];
})

// And average each column out

console.log([average(lats), average(longs)])

Example

Answer 1

这应该得到任何centroid的area的polygon

/*jslint sub: true, maxerr: 50, indent: 4, browser: true */
/*global console */

(function () {
    "use strict";

    function Point(x, y) {
        this.x = x;
        this.y = y;
    }

    function Region(points) {
        this.points = points || [];
        this.length = points.length;
    }

    Region.prototype.area = function () {
        var area = 0,
            i,
            j,
            point1,
            point2;

        for (i = 0, j = this.length - 1; i < this.length; j=i,i++) {
            point1 = this.points[i];
            point2 = this.points[j];
            area += point1.x * point2.y;
            area -= point1.y * point2.x;
        }
        area /= 2;

        return area;
    };

    Region.prototype.centroid = function () {
        var x = 0,
            y = 0,
            i,
            j,
            f,
            point1,
            point2;

        for (i = 0, j = this.length - 1; i < this.length; j=i,i++) {
            point1 = this.points[i];
            point2 = this.points[j];
            f = point1.x * point2.y - point2.x * point1.y;
            x += (point1.x + point2.x) * f;
            y += (point1.y + point2.y) * f;
        }

        f = this.area() * 6;

        return new Point(x / f, y / f);
    };

    var polygon = [
            {"x": -1.2, "y": 5.1},
            {"x": -1.3, "y": 5.2},
            {"x": -1.8, "y": 5.9},
            {"x": -1.9, "y": 5.8}
        ],
        region = new Region(polygon);

    console.log(region.centroid());
}());

在jsfiddle

上

Answer 2

这将获得任何形状的中心点和数组[centerX，centerY]：

var center = function (arr)
{
    var minX, maxX, minY, maxY;
    for (var i = 0; i < arr.length; i++)
    {
        minX = (arr[i][0] < minX || minX == null) ? arr[i][0] : minX;
        maxX = (arr[i][0] > maxX || maxX == null) ? arr[i][0] : maxX;
        minY = (arr[i][1] < minY || minY == null) ? arr[i][1] : minY;
        maxY = (arr[i][1] > maxY || maxY == null) ? arr[i][1] : maxY;
    }
    return [(minX + maxX) / 2, (minY + maxY) / 2];
}

另一种方式：

var center = function (arr)
{
    var x = arr.map (function (a){ return a[0] });
    var y = arr.map (function (a){ return a[1] });
    var minX = Math.min.apply (null, x);
    var maxX = Math.max.apply (null, x);
    var minY = Math.min.apply (null, y);
    var maxY = Math.max.apply (null, y);
    return [(minX + maxX) / 2, (minY + maxY) / 2];
}
getCenter (coords);

或者，如果您的浏览器支持ECMAScript 6，那么您可以使用Arrow functions和Spread syntax，如下所示：

var center = function (arr)
{
    var x = arr.map (x => x[0]);
    var y = arr.map (x => x[1]);
    var cx = (Math.min (...x) + Math.max (...x)) / 2;
    var cy = (Math.min (...y) + Math.max (...y)) / 2;
    return [cx, cy];
}

jsfiddle

Answer 3

要在Google Maps API v3（未测试）中获取Polygon（包含您的数据）的边界：

var coords = [
  [ -1.2, 5.1 ],
  [ -1.3, 5.2 ],
  [ -1.8, 5.9 ],
  [ -1.9, 5.8 ]
];

var bounds = new google.maps.LatLngBounds();
for (var i = 0; i<coords.length; i++) {
   bounds.extend(new google.maps.LatLng(coords[i][0], coords[i][1]));
}
var center = bounds.getCenter();

Answer 4

我意识到这并不是你想要的，但如果没有其他人回答它可能会有所帮助。这是一个PHP函数，我用它来为我的地图应用程序找到多边形的中心点。它应该很容易转换为javascript供您使用。

function getCenter($coord_array){
    $i = 0;
    $center = $coord_array[0];
    unset($coord_array[0]);
    foreach($coord_array as $key => $coord){    
        $plat = $coord[0];
        $plng = $coord[1];
        $clat = $center[0];
        $clng = $center[1];
        $mlat = ($plat + ($clat * $i)) / ($i + 1);
        $mlng = ($plng + ($clng * $i)) / ($i + 1);
        $center = array($mlat, $mlng);
        $i++;
    }
    return array($mlat, $mlng);
}

请注意，必须关闭多边形，这意味着数组中的第一个点和数组中的最后一个点是相同的。

将坐标字符串转换为必要数组的函数：

function coordStringToArray($coord_string)
{
    $coord_array = explode("\n",$coord_string);
    foreach($coord_array as $key => $coord){
        $coord_array[$key] = explode(', ',$coord);
    }
    return $coord_array;
}

原始坐标字符串的示例：

42.390576, -71.074258
42.385822, -71.077091
42.382461, -71.079408
42.382018, -71.081468
42.380496, -71.080953
42.380433, -71.076576
42.373902, -71.073915
42.373078, -71.069967
42.369273, -71.064216
42.368892, -71.062328
42.369527, -71.056491
42.370288, -71.050741
42.371619, -71.047908
42.376185, -71.046278
42.383476, -71.045763
42.386139, -71.050483
42.386202, -71.057693
42.387597, -71.066534
42.390259, -71.072284
42.391210, -71.073658

Answer 5

这是我的es6解决方案，用于平均一组纬度和经度。平均不是确切的中心点，但就我而言，它可以完成工作。

getLatLonCenterFromGeom = (coords) => {
    const arrAvg = arr => arr.reduce((a,b) => a + b, 0) / arr.length;

    const centerLat = arrAvg(coords.map(c=>c.latitude));
    const centerLon = arrAvg(coords.map(c=>c.longitude));

    if (isNaN(centerLat)|| isNaN(centerLon))
        return null;
    else return {latitude: centerLat, longitude:centerLon};
}

在JavaScript中查找多边形的中心点

5 个答案: