在JavaScript中查找多边形的中心点 [英] Find centerpoint of polygon in JavaScript

问题描述

伦敦说，我有一个谷歌地图上的地点对象，它有一组坐标代表给定位置的边界框。每一组坐标都有经度和纬度。

我已经写了下面的代码来找到中心点，但我不确定它是否真的产生了中心点。如果多边形有5点而不是4点会怎么样？此外，这可以通过更有效的方式完成，操作更少吗？

 函数average（array）{
 //数组，然后除以长度
 return _.reduce（array，function（sum，num）{
 return sum + num; 
}，0）/ array.length; 
} 
 
 //我有一个二维数组，我想得到
 $ b的平均值var coords = [
 [-1.2， 5.1]，
 [-1.3,5.2]，
 [-1.8,5.9]，
 [-1.9,5.8] 
] 
 
 //所以我得到第一列
 
 var lats = coords.map（function（coord）{
 return coord [0]; 
}）
 
 //然后第二个
 
 var longs = coords.map（function（coord）{
 return coord [1]; 
}）
 
 / /并且每列的平均值为
 
 console.log（[average（lats），average（longs）]）
  

示例。

解决方案

这应该得到质心任何区域。 Polygonrel =noreferrer> polygon

  / * jslint sub： true，maxerr：50，indent：4，browser：true * / 
 / *全局控制台* / 
 
（function（）{
use strict; 
 
函数Point（x，y）{
 this.x = x; 
 this.y = y; 
} 
 
函数Region（points）{
 this.points = points || []; 
 this.length = points.length; 
} 
 
 Region.prototype.area = function（）{
 var area = 0，
i，
j，
 point1，
 point2; （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; 
 
返回区域; 
}; 
 
 Region.prototype.centroid = function（）{
 var x = 0，
y = 0，
i，
j，
f，
 point1，
 point2; （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; 
 
返回新的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区域（多边形）; 
 
 console.log（region.centroid（））; 
}（））; 
  

在 jsfiddle

I have a "place" object from Google Maps which has a set of coordinates that represent a bounding box for a given location, say London. Each set of coordinates has a latitude and longitude.

I have written the below code to find the centerpoint, but I am not sure if it does actually produce the centerpoint. What if the polygon has 5 points instead of 4? Also, can this be done in a more efficient way, with less operations?

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.

解决方案

This should get the centroid of the area of any 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());
}());

On jsfiddle

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