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Highly Accurate Estimation of Lower Part Tree Trunk Perimeter by SfM Photogrammetry for Annual Tree increment Estimation

Our research is focusing on the methodology development of individual tree image acquisition with emphasis to achieve high precision of perimeter estimation using Structure from Motion (SfM) photogrammetry. Furthermore, we are investigating the potential to estimate the annual increment of mature trees. We captured four tree species (Fagus sylvatica, Quercus petraea, Picea abies and Abies alba). Ten trees per species. A perimeter was measured at three heights (0.8 m. 1.3 m and 1.8 m) by conventional methods (measuring tape). We have used the standard approach within Agisoft Photoscan Professional to process images to point clouds. Then we have used DendroCloud software (1) to deliver the cross-sections for further analyses. Cross-sections were processed within ArcGIS for Desktop where the convex hull was used to estimate the perimeters. In the first stage, we have compared two different lenses. Fisheye and non-fisheye (Canon EF 8–15 mm f/4L and Canon EF 35 mm f/2). The best approach was chosen based on the accuracy of perimeter estimation. In overall, the best approach was when the fisheye lens was used. The best accuracy of estimation based on root mean square error was achieved for Fagus sylvatica at 1.3 m height (RMSE of 0.25 cm) (2). Based on the results, we have used in the following stage the fisheye lens which was most accurate and time efficient. In the second stage, we captured images and measured trees before and after the vegetation period. Then we have calculated annual increment and compared the increment for each tree species. We have used a t-test to statistically verify the agreement of used approaches (SfM versus conventional). Only in the case of Quercus petraea was a statistically significant difference between those two. In our opinion, the reason is the rough surface of the bark. On the other hand, the annual increment of mature trees is relatively low and even with conventional methods, the accuracy is questionable. In further research, we would like to take increment cores and used them as the third most accurate approach.

1. Koreň, M.; Mokroš, M.; Bucha, T. Accuracy of tree diameter estimation from terrestrial laser scanning by circle-fitting methods. Int. J. Appl. Earth Obs. Geoinf. 2017, 63, 122–128. 2. Mokroš, M.; Výbošťok, J.; Tomaštík, J.; Grznárová, A.; Valent, P.; Slavík, M.; Merganič, J. High Precision Individual Tree Diameter and Perimeter Estimation from Close-Range Photogrammetry. Forests 2018, 9, 696.

Martin Mokroš
Czech University of Life Sciences Prague
Czech Republic

Jozef Výbošťok
Technical University in Zvolen
Slovakia

Alžbeta Grznárová
Technical University in Zvolen
Slovakia

 


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