Design and test of photographic dendrometer based on Ultra Wide Band positioning

Estimation of trees position and Diameter at Breast Height (DBH) is an important part of forest resources inventory. This study aimed to design a multi-functional, high-precision, real-time positioning tree-measuring device that integrates plot setting, DBH measurement, and tree position measurement based on the Ultra Wide Band(UWB) positioning principle, sensor technology, image processing technology, trigonometric functions and tree surveying theories. The main hardwares component of the equipment included CCD (Charge Coupled Device) image acquisition module, antenna, three-axis gyroscope module, three-axis accelerometer module and console module, the auxiliary components included fixed cloud platform and lithium battery. The software was developed by a modular structure compiled in android windows development environment based on the C++ language. According to the matching characteristics of the photogrammetric image feature points, the "surround shooting" sample plot observation method was proposed. The pix4D commercial software was used to established the three-dimensional point cloud model of the trees, and the LiDAR360 software was used to denoise the reconstructed 3D point cloud, extract the DBH and the position of the trees. In order to verify the accuracy of stand parameter extraction, the device was tested in four plots, that was Salix matsudana Koidz, Pinus tabuliformis Carr, Quercus mongolica and Koelreuteria Paniculat respectively. The results showed that the designed photographic dendrometer could be used to obtain the image of the trees and coordinate information in image quickly, the deviation and RMSE (Root Mean Squared Error) of the DBH were -0.04-0.42 cm and 0.26-0.51 cm, and that of the position were -0.16-0.27 m and 0.23-0.34 m, respectively, the measuring precision conformed to the requirements of forestry investigation. The study can provide a reference for the forest survey.