public function distanceMultiplier($distanceMultiplier)
    {
        if ($this->query['type'] !== Query::TYPE_GEO_NEAR) {
            throw new BadMethodCallException('This method requires a geoNear command (call geoNear() first)');
        }

        $this->query['geoNear']['options']['distanceMultiplier'] = $distanceMultiplier;
        return $this;
    }