## 6 Conclusions  
This study aims to derive an optimal route for robot-based delivery service at tourist destinations. The mathematical model-based optimization technique is applied to generate such an optimal route which maximizes total customer satisfaction. Two cases are analyzed in the aspect of safety concerns. Each case stands for the case assuming UAVs freely fly through entire nodes and the case assuming UAVs only move through the outline of the beach, respectively. Both cases are tested by controlling the number of vehicles and the number of orders assigned to find out the validity of the proposed mathematical model. The results of the small size problem show that the orders tend to be assigned to the UAVs due to less travel time to arrive at each node compared to UGVs. Additionally, even some distant nodes where UGVs can reach earlier are assigned to UAVs. This is due to higher fundamental satisfaction when the service is done compared to UGVs and a lower decrease in satisfaction per delivery time. This implies that minimizing arrival time does not always match customer needs. However, in Case 2, it is found that the number of assigned orders to UGVs has increased. It is because, unlike Case 1, available routes for UAVs have been restricted to the outline of the beach. The slower movement speed of UGVs decreases customer satisfaction. Even in the nodes where orders are assigned to UAVs, customer satisfaction has decreased because of the limited available direction for UAVs. The results of the reasonable size problem well reflect the characteristics discussed for the small size problem. The overall customer satisfaction is 11.89% higher in Case 1 and the complete time of service is 39.91% lower in Case 2. The orders are preferentially assigned to UAVs when there are no restrictions compared to the case with restrictions. However, the result of the reasonable size problem implies that if there are more orders to deal with, the number of order assignment to UGVs increase because of the larger capacity of the weight and volume. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Vehicle**} & \multirow{2}{*}{**Round**} & \multicolumn{2}{c}{**Travel Schedule:**} & \multirow{2}{*}{**Satisfaction**} & \multicolumn{2}{c}{**Total**} & \multicolumn{1}{c}{**CPU**} \\  & & & **Node (Type of Goods)** & & & **Time** & **(Second)** \\ \hline \multirow{8}{*}{Case 1} & UAV1 & 1 st & \(0\to 9(1)\to 3(1)\to 4(1)\to 4(2)\to 0\) & & & 591.47 \\  & 2 nd & & \(0\to 2(2)\to 11(2)\to 0\) & & & \\  & UAV2 & 1 st & \(0\to 1(1)\to 9(1)\to 6(1)\to 13(1)\to\) & & & \\  & & & \(13(2)\to 0\) & & & \\  & & 2 nd & \(0\to 14(2)\to 0\) & \(14.68\) & 474.30 & \\  & & 1 st & \(0\to 7(1)\to 20(1)\to 19(2)\to 0\) & & & \\  & UAV3 & 2 nd & \(0\to 16(2)\to 18(2)\to 0\) & & & \\  & UGV1 & 1 st & \(0\to 15(2)\to 0\) & & & \\  & UGV2 & 1 st & \(0\to 15(1)\to 0\) & & & \\  & UGV3 & 1 st & \(0\to 9(2)\to 0\) & & & \\  & UAV1 & 1 st & \(0\to 7(1)\to 14(2)\to 0\) & & & 530.26 \\  & UAV1 & 2 nd & \(0\to 2(2)\to 0\) & & & \\  & UAV2 & 1 st & \(0\to 1(1)\to 4(1)\to 4(2)\to 19(2)\to 0\) & & & \\ Case 2 & UAV3 & 1 st & \(0\to 3(1)\to 6(1)\to 0\) & 13.12 & 285 & \\  & UGV1 & 1 st & \(0\to 9(1)\to 9(2)\to 16(2)\to 18(2)\to 0\) & & & \\  & UGV2 & 1 st & \(0\to 15(1)\to 15(2)\to 20(1)\to 0\) & & & \\  & UGV3 & 1 st & \(0\to 9(1)\to 11(2)\to 13(1)\to 13(2)\to 0\) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The result of reasonable size problem. This study is expected to become an essential source for practitioners to get insights when designing integrated goods delivery systems for UGVs and UAVs at tourist destinations. Such considerations include the suitable number of UGVs and UAVs in the aspect of customer satisfaction and availability of each vehicle. Furthermore, by considering components including multiple types of goods, safety concerns, limited capacity of vehicles, and upper limit time for service, the proposed mathematical model is expected to be practical for real-world application.