In drone photography of vast natural terrain, it is difficult to know in advance the exact location and shape of an object. In addition, there are many time and location constraints in such environments; therefore, it is desirable to capture images quickly by automatic flight. The authors had previously proposed a method to determine the safety of such an automatic flight photography plan in advance and capture photographs quickly. The method was designed to model an object from the safety zone using multiple drones and determine a safe path in advance. However, further improvement in the efficiency was necessary when photographing the object over a large area. In contrast, in this study, to improve the efficiency of the safe flight path determination method for large-scale subjects, we developed a new method to model each number of photographs using structure from motion (SfM) and verify the accuracy of the model obtained for each number of photographs in advance. In addition, by determining the appropriate number of shots based on the results obtained and reducing the loss of time and battery during shooting, we verified the extent to which the total flight time could be reduced for a flight path of shooting a large-scale object in the Esan Prefectural Natural Park. In the case of the Esan Prefectural Natural Park, we demonstrate that the difference in the small-object shooting time was not a problem, but the difference was significant for shooting large objects. The effectiveness of determining and applying, in advance, the number of shots that provides appropriate accuracy is demonstrated.

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