pocketmine\level\format\generic\BaseFullChunk::getHighestBlockAt PHP Method

    public function getHighestBlockAt($x, $z, $cache = true)
    {
        if ($cache) {
            $h = $this->getHeightMap($x, $z);
            if ($h !== 0 and $h !== 127) {
                return $h;
            }
        }
        $column = $this->getBlockIdColumn($x, $z);
        for ($y = 127; $y >= 0; --$y) {
            if ($column[$y] !== "") {
                $this->setHeightMap($x, $z, $y);
                return $y;
            }
        }
        return 0;
    }