protected function checkIfPointLabelExists($label, $isMultiPoint)
    {
        $labelExists = false;
        $stack = ($isMultiPoint) ? $this->multiPointStack : $this->pointStack;
        foreach ($stack as $point)
        {
            if($point->getLabel() == $label)
            {
                $labelExists = true;
                break;
            }
        }

        if($labelExists)
        	throw new \InvalidArgumentException("label '" . $label . "' already exists, choose new point label.");
    }