public function toString() : string
    {
        $string = "solid " . $this->getSolidName() . "\n";

        $count = $this->getFacetNormalCount();

        for ($i = 0; $i < $count; $i++) {
            $string .= $this->getFacetNormal($i)->toString() . "\n";
        }

        $string .= "endsolid";

        return $string;
    }