*3.3. Selecting the Best Coverage Direction (s) by Analyzing the Span of the Area of Interest and Exploiting Free Spaces Geometry Information*

Selecting the best coverage direction is extremely important to reduce the number of turns in the flight path to preserve the UAV resources. The turns are costly in terms of the energy, mission time, and path length because the UAV has to reduce the speed, perform turn, and increase speed again. Figure 5 presents the overview of the coverage path obtained from the same AOI with two different directions. The path on the left has only three turns and the path on the right has eleven turns.

**Figure 5.** Overview of the coverage path obatined through two different sweep directions.

In this work, we select the best coverage direction (s) by analyzing the span *D* of the AOI and exploiting free spaces' geometry information. We compute the horizontal span *Hs* and vertical span *Vs* of the AOI for the best coverage direction selection for regular shaped AOI. Additionally, we exploit the free spaces' geometry knowledge to select the appropriate coverage direction (s). The coverage direction is chosen parallel to the maximal span axis and considering the free spaces tendency. We employ either one or multiple coverage directions depending upon the AOI complexity to reduce the number of turns. For the irregular shaped AOI, we compute the convex-hull and transform it to some approximate regular shape for the span calculation and best coverage direction selection. When both spans of the AOI are equal, the appropriate coverage direction is chosen considering the obstacles placement and free spaces tendency. By utilizing the global information about the AOI and following the procedure explained above, the best coverage direction can be selected which yields a smaller number of turns in the path. The proposed method utilizes the cumulative knowledge of the several parts of the AOI to find the best coverage direction which reduces the number of turns significantly.
