root/g-map/files/lib/data/gmap/GmapCluster.class.php @ 1226

<?php

/**
 * gets several positions and returns a clustered array
 *
 * @author      Torben Brodt
 * @license     GNU General Public License <http://opensource.org/licenses/gpl-3.0.html>
 */
class GmapCluster {

        const OFFSET = 268435456;
        const RADIUS = 85445659.4471; /* $self::OFFSET / pi() */
        
        protected $distance;
        protected $zoom;
        
        /**
         *
         * @param       $distance       Distance in pixel inside which markers will be clustered.
         * @param       $zoom           Current map zoom level.
         */
        public function __construct($distance, $zoom) {
                $this->distance = $distance;
                $this->zoom = $zoom;
        }
        
        protected function lonToX($lon) {
                return round(self::OFFSET + self::RADIUS * $lon * pi() / 180);          
        }

        protected function latToY($lat) {
                return round(self::OFFSET - self::RADIUS * log((1 + sin($lat * pi() / 180)) / (1 - sin($lat * pi() / 180))) / 2);
        }

        protected function pixelDistance($lat1, $lon1, $lat2, $lon2, $zoom) {
                $x1 = $this->lonToX($lon1);
                $y1 = $this->latToY($lat1);

                $x2 = $this->lonToX($lon2);
                $y2 = $this->latToY($lat2);
                
                return sqrt(pow(($x1-$x2),2) + pow(($y1-$y2),2)) >> (21 - $zoom);
        }
        
        /**
         * Return average center of markers
         *
         * @return   object Google_Maps_Coordinate
         */
        protected function getCluster(array $markers) {
                $count = count($markers);

                /* Calculate average lat and lon of markers. */
                $lat_sum = $lon_sum = 0;
                foreach ($markers as $marker) {
                   $lat_sum += $marker['lat'];
                   $lon_sum += $marker['lon'];
                }
                $lat_avg = $lat_sum / $count;
                $lon_avg = $lon_sum / $count;
                
                return array(
                        'count' => $count,
                        'lat' => $lat_avg,
                        'lon' => $lon_avg
                );
        }

        /**
         *
         * @param       $markers        Array of lat and lon locations.
         */
        public function getMarkers(array $markers) {
                $clustered = array();

                /* Loop until all markers have been compared. */
                while (count($markers)) {
                        $marker  = array_pop($markers);
                        $cluster = array();

                        /* Compare against all markers which are left. */
                        foreach ($markers as $key => $target) {
                                $pixels = $this->pixelDistance($marker['lat'], $marker['lon'], $target['lat'], $target['lon'], $this->zoom);

                                /* If two markers are closer than given distance remove */
                                /* target marker from array and add it to cluster.        */
                                if ($this->distance > $pixels) {
                                        unset($markers[$key]);
                                        $cluster[] = $target;
                                }
                        }

                        /* If a marker has been added to cluster, add also the one  */
                        /* we were comparing to and remove the original from array. */
                        if (count($cluster) > 0) {
                                $cluster[] = $marker;
                                $clustered[] = $this->getCluster($cluster);
                        } else {
                                $clustered[] = $marker;
                        }
                }
                return $clustered;
        }
}