public function getMarkerId($marker, $prefix = null)
	{
		$marker = $this->pointToIndArray($marker);
		$key = substr(md5($marker[0] . $marker[1]), 0, 6);

		if (!isset($this->_markerId[$key])) {
			$this->_markerId[$key] = 'mk' . $this->mapId . static::$markerCount++;

			if ($prefix) {
				$this->_markerId[$key] = $prefix . ucfirst($this->_markerId[$key]);
			}
		}

		return $this->_markerId[$key];
	}