Article Figures & Data
Figures
- Figure 1.
Photograph of the commercially available hobby drone, a DJI Mini 2® (DJI, Shenzhen, China) UAV, which was used for this study.
- Figure 2.
A: 3D model of a split oak branch suspended from a timber gantry crane. B: Example measurement along the surface of the 3D model of the branch, carried out within the software program 3DF Zephyr Lite Steam Edition (3Dflow SRL, Verona, Italy).
- Figure 3.
The 4 subject oak trees used in the field trial: T1, top left; T2, top right; T3, bottom left; and T4, bottom right. These were all open-grown trees in a parkland setting.
- Figure 4.
Visual representation of the 3 different flight strategies used in this study, where the blue shapes represent camera positions. A: Orbital. B: Cluster. C: Parallel.
- Figure 5.
Screenshot of the T1 FOI models represented as RGB scalar fields within CloudCompare (EDF R&D, Los Altos, CA, USA).
- Figure 6.
Visual comparison between the rendered models for the 4 FOIs (T1, T2, T3, T4) in the order of orbital flight, cluster flight, and parallel flight. For each of the 4 FOIs, the parallel flights provided the most detailed rendering of the shape and surfaces of the FOIs within the photogrammetric models.
- Figure 7.
Images of all 4 FOIs for all 3 flight strategies. The rows represent the FOIs for T1, T2, T3, and T4, respectively. The columns represent the photogrammetric models from the orbital flight, cluster flight, and parallel flight strategies, respectively. In all 4 cases, the level of visual detail and accuracy is noticeably better for the images generated from the parallel flight strategy.
- Figure 8.
Camera maps (camera positions marked in blue) for T1 and T2 parallel flights around FOIs. A: Camera map for the T1 parallel flight, which shows that images taken all around the FOI were used for the photogrammetric model. B: Corresponding camera map for the parallel flight of T2, where the images used for the model were only situated on one side of the FOI, limiting the associated model’s accuracy.
Tables
- Table 1.
Number of images captured and used in each FOI (feature of interest) photometry model. UAV (uncrewed aerial vehicle).
FOI tree and flight strategy No. of images taken by UAV No. of images used in model % of used images from total images T1 orbital 341 339 99.4% T1 cluster 159 38 23.9% T1 parallel 221 119 53.8% T2 orbital 345 345 100.0% T2 cluster 174 67 38.5% T2 parallel 276 158 57.2% T3 orbital 406 406 100.0% T3 cluster 268 268 100.0% T3 parallel 248 248 100.0% T4 orbital 344 344 100.0% T4 cluster 178 42 23.6% T4 parallel 275 273 99.3% - Table 2.
Mean point density for each model generated from the field study, with standard deviation and coefficient of variation. FOI (feature of interest).
FOI ref Mean point density Standard deviation Coefficient of variation T1 orbital 1.007 0.115 0.114 T2 orbital 1.075 0.418 0.389 T3 orbital 1.223 0.602 0.492 T4 orbital 1.911 1.322 0.692 T1 cluster 4.627 2.046 0.442 T2 cluster 4.725 3.799 0.804 T3 cluster 5.074 2.445 0.482 T4 cluster 28.027 35.091 1.252 T1 parallel 32.719 17.719 0.542 T2 parallel 33.840 22.314 0.659 T3 parallel 15.400 6.469 0.420 T4 parallel 35.765 29.078 0.813
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