如何在谷歌地图上找到网格线的中心

Question

我正在努力解决一些 GIS 信息的问题，我试图将这些信息放入 KML 文件中以供谷歌地图和谷歌地球使用。

我有一个包含大量调查的 SQL 数据库，这些调查按行存储。当所有线条都绘制在地图上时，它们会创建一个网格。我想做的是计算出这些“网格”的中心，以便我可以将地标引用放入 kml 中以显示地图上的所有网格位置。

线在数据库中的存储方式如下：

118.718318,-19.015803,0 118.722449,-19.016919,0 118.736223,-19.020637,0 118.749936,-19.024023,0 118.763897,-19.027722,0 118.777705,-19.031277,0 118.791416,-19.034826,0 118.805276,-19.038367,0 118.818862,-19.041962,0 118.832862,-19.045582,0 118.846133,-19.049563,0 118.859801,-19.053851,0 118.873322,-19.058145,0 118.887022,-19.062349,0 118.900595,-19.066594,0 118.914066,-19.070839,0 118.927885,-19.075151,0 118.941468,-19.079354,0 118.955064,-19.083658,0 118.968766,-19.087896,0 118.982247,-19.092054,0 118.995795,-19.096324,0 119.009192,-19.100448,0 119.022805,-19.104787,0 119.036414,-19.10893,0 119.049625,-19.113166,0 119.063155,-19.11738,0 119.076626,-19.121563,0 119.090079,-19.125738,0 119.103679,-19.129968,0 119.117009,-19.134168,0 119.130637,-19.138418,0 119.144134,-19.142613,0 119.157749,-19.146767,0 119.171105,-19.151058,0 119.184722,-19.155252,0 119.19844,-19.159399,0 119.211992,-19.163737,0 119.225362,-19.167925,0 119.239109,-19.17218,0 119.252552,-19.176239,0 119.265975,-19.180483,0 119.279718,-19.184901,0 119.2931,-19.189118,0 119.306798,-19.193267,0 119.320561,-19.197631,0 119.33389,-19.201898,0 119.34772,-19.206063,0 119.361322,-19.210282,0 119.374522,-19.214505,0 119.38825,-19.218753,0 119.401948,-19.22299,0 119.415609,-19.227171,0 119.42913,-19.231407,0 119.44269,-19.235604,0 119.456221,-19.240254,0 119.469772,-19.244165,0 119.483159,-19.248341,0 119.496911,-19.252483,0 119.510569,-19.256818,0 119.524034,-19.261068,0 119.537822,-19.265332,0 119.551409,-19.269529,0 119.564744,-19.273764,0 119.578357,-19.277874,0 119.591935,-19.282171,0 119.605472,-19.286424,0 119.619009,-19.290593,0 119.632777,-19.294862,0 119.646394,-19.299146,0 119.660107,-19.303469,0 119.673608,-19.307602,0 119.6872,-19.31182,0 119.700838,-19.31605,0 119.714555,-19.320301,0 119.728202,-19.324615,0 119.741511,-19.328794,0 119.755299,-19.333098,0 119.768776,-19.337206,0 119.782216,-19.341528,0 119.796141,-19.345829,0 119.809691,-19.349879,0 119.822889,-19.354112,0 119.836822,-19.358414,0 119.850077,-19.362618,0 119.864069,-19.366916,0 119.8773,-19.371092,0 119.891263,-19.37536,0 119.904612,-19.379556,0 119.918522,-19.38394,0 119.932101,-19.388108,0 119.945577,-19.392184,0 119.959304,-19.396544,0 119.973042,-19.400809,0 119.986433,-19.405015,0 119.999196,-19.408981,0 120.011959,-19.412946,0 120.014512,-19.41374,0  
118.990393,-19.523933,0 118.990833,-19.522296,0 118.994368,-19.509069,0 118.997911,-19.49589,0 119.001249,-19.48258,0 119.004939,-19.469658,0 119.008437,-19.456658,0 119.01183,-19.443361,0 119.015332,-19.430439,0 119.01869,-19.417491,0 119.022303,-19.40421,0 119.025853,-19.391381,0 119.029387,-19.377966,0 119.032821,-19.365006,0 119.036247,-19.352047,0 119.039935,-19.338701,0 119.043376,-19.325781,0 119.046824,-19.312713,0 119.050223,-19.299634,0 119.053822,-19.286711,0 119.05736,-19.273441,0 119.060722,-19.260467,0 119.064357,-19.247382,0 119.067863,-19.234069,0 119.071361,-19.221168,0 119.07486,-19.208268,0 119.078303,-19.19503,0 119.081721,-19.181915,0 119.085296,-19.169016,0 119.088851,-19.155937,0 119.092245,-19.142828,0 119.095887,-19.12944,0 119.099337,-19.116291,0 119.102821,-19.103421,0 119.106333,-19.090384,0 119.109885,-19.077356,0 119.113395,-19.063976,0 119.116866,-19.050973,0 119.120467,-19.037886,0 119.123751,-19.024888,0 119.127385,-19.011622,0 119.130775,-18.998856,0 119.134503,-18.98547,0 119.13873,-18.9728,0 119.14289,-18.959666,0 119.146076,-18.946541,0 119.149065,-18.933693,0 119.152281,-18.920522,0 119.155414,-18.907033,0 119.158442,-18.894058,0 119.161421,-18.88097,0 119.164632,-18.867484,0 119.167668,-18.854501,0 119.170744,-18.841401,0 119.173939,-18.827999,0 119.17703,-18.815028,0 119.17984,-18.802218,0 119.182902,-18.789334,0 119.186088,-18.776136,0 119.189031,-18.762862,0 119.192179,-18.749824,0 119.19539,-18.7365,0 119.198255,-18.723279,0 119.201476,-18.710134,0 119.204345,-18.69705,0 119.20746,-18.683768,0 119.210555,-18.670607,0 119.213641,-18.657632,0 119.216727,-18.644301,0 119.21982,-18.630956,0 119.223094,-18.617243,0 119.22625,-18.603885,0 119.229368,-18.590534,0 119.232494,-18.577364,0 119.235477,-18.564287,0 119.238496,-18.550953,0 119.241392,-18.53789,0 119.244609,-18.524881,0 119.247551,-18.512017,0 119.250532,-18.498916,0 119.253729,-18.485859,0 119.256428,-18.473845,0 119.259288,-18.461645,0 119.262064,-18.4491,0 119.265024,-18.437048,0 119.267877,-18.424992,0 119.270457,-18.4136,0 119.273429,-18.401305,0 119.276346,-18.388484,0 119.279506,-18.375299,0 119.282307,-18.362197,0 119.285494,-18.34918,0 119.288695,-18.336115,0 119.291008,-18.323772,0 119.294026,-18.310635,0 119.297332,-18.297714,0 119.300499,-18.284553,0 119.303442,-18.271193,0 119.307081,-18.258278,0 119.309945,-18.245139,0 119.313121,-18.232137,0 119.31642,-18.218993,0 119.319499,-18.205722,0 119.322801,-18.192774,0 119.325986,-18.179558,0 119.329173,-18.166332,0 119.33236,-18.15312,0 119.335558,-18.140071,0 119.338761,-18.126696,0 119.342007,-18.113502,0 119.345238,-18.100349,0 119.34808,-18.088343,0 119.350259,-18.079138,0
119.912412,-18.177179,0 119.910223,-18.183223,0 119.905619,-18.195973,0 119.901171,-18.208645,0 119.896641,-18.221452,0 119.89198,-18.234323,0 119.887547,-18.246912,0 119.882922,-18.259925,0 119.878421,-18.272522,0 119.873909,-18.285223,0 119.869264,-18.298194,0 119.864746,-18.310939,0 119.860203,-18.323628,0 119.855692,-18.336434,0 119.850997,-18.349262,0 119.846561,-18.362014,0 119.841916,-18.374866,0 119.837406,-18.387565,0 119.832778,-18.400657,0 119.828259,-18.413072,0 119.82364,-18.426273,0 119.819088,-18.438992,0 119.814546,-18.451696,0 119.810103,-18.464425,0 119.80548,-18.477041,0 119.800935,-18.48989,0 119.796359,-18.502741,0 119.791812,-18.515489,0 119.787314,-18.528536,0 119.782724,-18.540965,0 119.778079,-18.553994,0 119.773558,-18.56663,0 119.768931,-18.57955,0 119.76446,-18.592177,0 119.759793,-18.605255,0 119.755393,-18.617736,0 119.750648,-18.630757,0 119.746479,-18.643371,0 119.741779,-18.656176,0 119.737071,-18.669135,0 119.732572,-18.681798,0 119.727954,-18.694669,0 119.723453,-18.707473,0 119.718855,-18.720259,0 119.714169,-18.733198,0 119.70946,-18.746355,0 119.704998,-18.759005,0 119.700581,-18.771793,0 119.696226,-18.784893,0 119.691577,-18.797373,0 119.68662,-18.810064,0 119.682182,-18.822772,0 119.677711,-18.835621,0 119.672955,-18.848475,0 119.668536,-18.861252,0 119.663856,-18.873901,0 119.659412,-18.88663,0 119.654815,-18.899592,0 119.650185,-18.912338,0 119.645586,-18.925118,0 119.640925,-18.937923,0 119.636617,-18.950753,0 119.631874,-18.963446,0 119.627376,-18.976275,0 119.622845,-18.98893,0 119.618175,-19.001942,0 119.613727,-19.014668,0 119.608878,-19.027398,0 119.60445,-19.039954,0 119.599954,-19.053249,0 119.595066,-19.066008,0 119.590562,-19.078866,0 119.586062,-19.091703,0 119.58155,-19.104199,0 119.576948,-19.116924,0 119.572431,-19.129926,0 119.567449,-19.142699,0 119.563227,-19.155474,0 119.558555,-19.168309,0 119.553956,-19.181053,0 119.549545,-19.193649,0 119.544854,-19.20646,0 119.540133,-19.21929,0 119.535606,-19.232162,0 119.53108,-19.245054,0 119.526509,-19.257772,0 119.522079,-19.270427,0 119.517419,-19.283013,0 119.512755,-19.296126,0 119.508159,-19.309031,0 119.503557,-19.321821,0 119.498966,-19.334394,0 119.494487,-19.347232,0 119.489815,-19.359907,0 119.485201,-19.372962,0 119.48067,-19.385811,0 119.476151,-19.398326,0 119.471526,-19.411138,0 119.466856,-19.424266,0 119.462284,-19.436788,0 119.457752,-19.449628,0 119.452975,-19.462718,0 119.448612,-19.47499,0 119.444249,-19.48726,0 119.439886,-19.499531,0 119.437704,-19.505666,0    

每个点都是进行测量的位置。

是否有 PHP 库或公式可以用来解决这个问题而不需要太深入？

谢谢

Answer 1

这很大程度上取决于你如何定义“中心”。您可能想尝试一种稍微复杂的方法：

1. 从线中提取点列表
2. 查找点的凸包：
3. 查找凸包的质心

_{（来源：algorithmic-solutions.info）}

凸包简单地描述为最简单的多边形，它穿过一些点，形成一个包围多边形内所有点的包络线。 维基百科有更严格的描述。

质心提供了一种简单的方法来查找多边形的“重心”。 wikipedia 和 一个很好的教程提供了更多信息。

Answer 2

或者，一个非常简单的实现可能会找到线条的最小边界矩形，然后找到盒子的几何中心。以下代码假设您上面发布的行表示为字符串，并且位于数组中。我不是 PHP 性能专家，但该算法应该在 O(n) 渐近时间内执行：

<?php

$line_strs = array(
"118.718318,-19.015803,0 118.722449,-19.016919,0 118.736223,-19.020637,0 118.749936,-19.024023,0 118.763897,-19.027722,0 118.777705,-19.031277,0",  "118.791416,-19.034826,0 118.805276,-19.038367,0 118.818862,-19.041962,0 118.832862,-19.045582,0 118.846133,-19.049563,0 118.859801,-19.053851,0",  
[SNIP majority of lines...]
"119.448612,-19.47499,0 119.444249,-19.48726,0 119.439886,-19.499531,0 119.437704,-19.505666,0");
$xs = array();
$ys = array();
foreach ($line_strs as $line){
    $points = explode(' ', $line);
    foreach ($points as $pt){
        $xyz = explode(',', $pt);  
        $xs[] = (float)$xyz[0];
        $ys[] = (float)$xyz[1]; 
    }
}
$x_mean = (max($xs) + min($xs)) / 2;
$y_mean = (max($ys) + min($ys)) / 2;
echo "$x_mean,$y_mean\n";
?>

输出 119.366415,-18.8015355。

Answer 3

质心 ？

如果我有时间，我会编辑这个答案以包含 python 实现

Answer 4

另一个非常简单的答案是找到所有顶点的平均位置。它有利于点密集的区域。这会返回与边界框方法略有不同的答案。您可能想尝试一下它们，看看哪个为您的数据提供了“更好”的结果。

<?php

$line_strs = array(
"118.718318,-19.015803,0 118.722449,-19.016919,0 118.736223,-19.020637,0 118.749936,-19.024023,0 118.763897,-19.027722,0 118.777705,-19.031277,0",  "118.791416,-19.034826,0 118.805276,-19.038367,0 118.818862,-19.041962,0 118.832862,-19.045582,0 118.846133,-19.049563,0 118.859801,-19.053851,0",  
[SNIP majority of lines...]
"119.448612,-19.47499,0 119.444249,-19.48726,0 119.439886,-19.499531,0 119.437704,-19.505666,0");
$x_sum = 0.0;
$y_sum = 0.0;
$n = 0;
foreach ($line_strs as $line){
    $points = explode(' ', $line);
    foreach ($points as $pt){
        $xyz = explode(',', $pt);  
        $x_sum += (float)$xyz[0];
        $y_sum += (float)$xyz[1]; 
        $n++;
    }
}
$x_mean = $x_sum / $n;
$y_mean = $y_sum / $n;
echo "$x_mean,$y_mean\n";
?>

这会输出 119.402034114,-18.9427670536。