检查点是否在多边形内 [英] Check if Point Is Inside A Polygon

问题描述

我想检查一个点是否位于特定的多边形内.多边形为:

I want to check if a point lies within a specific polygon. The polygon is:

 polygon=   [ [-73.89632720118, 40.8515320489962],
              [-73.8964878416508, 40.8512476593594],
              [-73.8968799791431, 40.851375925454],
              [-73.8967188588015, 40.851660158514],
              [-73.89632720118, 40.8515320489962] ]

我要检查的要点是:

1 = [40.8515320489962,-73.89632720118]
2 = [40.8512476593594,-73.8964878416508]
3 = [40.851375925454,-73.8968799791431]
4 = [40.851660158514,-73.8967188588015]
5 = [40.8515320489962,-73.89632720118]

如何确定这些点中的每一个是否都位于该多边形内?

How can I tell if each of these points lies within this polygon?

以下算法无效.我不知道为什么

The algorithm below does not work. I don't know why.

pt[lat,long]

function isPointInPoly(poly, pt){
    for(var c = false, i = -1, l = poly.length, j = l - 1; ++i < l; j = i)
        ((poly[i][1] <= pt[1] && pt[1] < poly[j][1]) || (poly[j][1] <= pt[1] && pt[1] < poly[i].y))
        && (pt[0] < (poly[j][0] - poly[i][0]) * (pt[1] - poly[i][1]) / (poly[j][1] - poly[i][1]) + poly[i][0])
        && (c = !c);
    return c;
}

我不想使用第三方解决方案，例如google maps API或

I don't want to use a third party solution such as google maps API or this one https://github.com/mattwilliamson/Google-Maps-Point-in-Polygon.

我的尝试在这里: http://jsfiddle.net/nvNNF/2/

推荐答案

在Github上有一个项目，代码为:

There is a project on Github with code: https://github.com/substack/point-in-polygon (MIT license):

function inside(point, vs) {
    // ray-casting algorithm based on
    // http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html

    var x = point[0], y = point[1];

    var inside = false;
    for (var i = 0, j = vs.length - 1; i < vs.length; j = i++) {
        var xi = vs[i][0], yi = vs[i][1];
        var xj = vs[j][0], yj = vs[j][1];

        var intersect = ((yi > y) != (yj > y))
            && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
        if (intersect) inside = !inside;
    }

    return inside;
};

用法:

// array of coordinates of each vertex of the polygon
var polygon = [ [ 1, 1 ], [ 1, 2 ], [ 2, 2 ], [ 2, 1 ] ];
inside([ 1.5, 1.5 ], polygon); // true

测试功能在这里: https://github. com/substack/point-in-polygon/blob/master/index.js

注意:当该点是多边形的一角或在一条边上时，此代码无法正常工作.这里有一个改进的版本: https://github.com/mikolalysenko/robust-point-多边形内

Note: This code doesn't work reliably when the point is a corner of the polygon or on an edge. There is an improved version here: https://github.com/mikolalysenko/robust-point-in-polygon

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