/**
* Increase the size the of the circle.
* @param int $amount
* @return boolean success|failure
*/
public function expand($amount = 1)
{
if ($this->precision == 1) {
// currently unwilling to expand to cover the entire globe
return false;
}
$this->precision = max($this->precision - $amount, 1);
// shrink the geohash, grow the box
$center = substr($this->center_geohash, 0, $this->precision);
$box = geohash::decode_box($center);
$dlat = $box->north - $box->south;
$dlon = $box->east - $box->west;
$set = new geohash_set();
$set->add($center);
$quadrant = geohash::quadrant($this->center_geohash, $this->precision);
if ($quadrant == geohash::northeast || $quadrant == geohash::northwest) {
// north side
$north = geohash::neighbor($center, geohash::north);
if ($north) {
$set->add_set(geohash::halve($north, geohash::south));
if ($quadrant == geohash::northeast) {
$set->add_set(geohash::quarter(geohash::neighbor($north, geohash::east), geohash::southwest));
} else {
// northwest
$set->add_set(geohash::quarter(geohash::neighbor($north, geohash::west), geohash::southeast));
}
$box->north += $dlat / 2;
}
} else {
// south side
$south = geohash::neighbor($center, geohash::south);
if ($south) {
$set->add_set(geohash::halve($south, geohash::north));
if ($quadrant == geohash::southeast) {
$set->add_set(geohash::quarter(geohash::neighbor($south, geohash::east), geohash::northwest));
} else {
// southwest
$set->add_set(geohash::quarter(geohash::neighbor($south, geohash::west), geohash::northeast));
}
$box->south -= $dlat / 2;
}
}
if ($quadrant == geohash::northeast || $quadrant == geohash::southeast) {
// east side
$set->add_set(geohash::halve(geohash::neighbor($center, geohash::east), geohash::west));
$box->east += $dlon / 2;
} else {
// west side
$set->add_set(geohash::halve(geohash::neighbor($center, geohash::west), geohash::east));
$box->west -= $dlon / 2;
}
$this->geohash_set = $set;
$this->max_radius = min($this->center->distance_to_longitude($box->east), $this->center->distance_to_longitude($box->west));
if ($box->north < 90) {
$this->max_radius = min($this->center->distance_to_latitude(min($box->north, 90)), $this->max_radius);
}
if ($box->south > -90) {
$this->max_radius = min($this->center->distance_to_latitude(max($box->south, -90)), $this->max_radius);
}
return true;
}
