A sample code for DBSCAN with haversine as distance

dbscan-haversine.php

<?php

/*
 * A sample program for DBSCAN with haversine as distance
 *
 * Requirements
 *   - PHP-ML (https://github.com/php-ai/php-ml)
 *   - php-geospatial (https://github.com/php-geospatial/geospatial)
 */

require_once __DIR__ . '/vendor/autoload.php';

use Phpml\Clustering\DBSCAN;
use Phpml\Math\Distance;

class Haversine implements Distance
{
    public function distance(array $a, array $b): float
    {
        return haversine(
            ['type' => 'Point', 'coordinates' => $a],
            ['type' => 'Point', 'coordinates' => $b]);
    }
}

$samples = [
    [0, 90 - 1e-6], [180, 90 - 1e-6],   // two samples near the north pole
    [-180 + 1e-6, 0], [180 - 1e-6, 0],  // two samples on the equator
    [0, -90 + 1e-6], [180, -90 + 1e-6], // two samples near the south pole
];

$dbscan = new DBSCAN($epsilon = 1, $min_samples = 2, new Haversine());
$clustered = $dbscan->cluster($samples);

foreach ($clustered as $i => $cluster) {
    echo "cluster $i: ", json_encode($cluster), "\n";
}

/*
 * cluster 0: [[0,89.999999],[180,89.999999]]
 * cluster 1: [[-179.999999,0],[179.999999,0]]
 * cluster 2: [[0,-89.999999],[180,-89.999999]]
 */