Single Wood Parameters Extraction and DBH Model Construction Based on UAV Tilt Photography Technology

The street tree area at the foot of Mount Ding in the campus of Nanjing Forest Police College was selected as the study area. Three-dimensional images of the area were obtained by using a five-eye camera mounted on a rotorwing UAV. The height and crown width of the sample trees in the three-dimensional images were extracted and measured by using Context Capture Center software. And the value measured by ground measuring equipment is used as the true value to verify the accuracy of the UAV tilt photography technology to obtain the parameters of a single wood. The results show that the average relative error of tree height and crown width extracted from 3D images obtained by UAV tilt photography is 3% and 2% respectively. In the 48 groups of fitting samples, the H&CW-DBH binary DBH inversion model has the highest coefficient of determination(R²), which is 0.9, and the minimum root mean square error(RMSE), which is 0.83. Among the 12 groups of test samples, the CW-DBH one-dimensional DBH inversion model has the lowest average error, which is only 0.63 cm, with an error rate of 4.8%. It can be seen that the binary DBH inversion model is the optimal DBH inversion model in this study. By extracting three parameters of tree height and crown width with UAV, the DBH value with higher accuracy can be obtained. It shows that the accuracy of tree height and crown width obtained by UAV stereophotography is high. UAV tilt photography technology can quickly obtain the forest resource information in the study area, reduce the field intensity of forestry workers, also provides a new technical reference for precision forestry inventory and forest land monitoring.