Study On Single Tree Structure Parameters Extraction Based On Close-range Photogrammetry

Single tree structure parameters reflect the growth trend and health status of the forest,which is of great significance to the management of the forest.The traditional measurement method of single tree structure parameters is time-consuming and laborious,so the close-range photogrammetry technology is introduced in this study,the purpose is to more easily and quickly extract the single tree structure parameters and restore the single tree structure morphology,so as to provide technical support for forest resources survey and tree three-dimensional model construction.In this study,the camera was first checked,and then the single tree structure parameters were extracted using the spatial forward intersection method.The SFM algorithm was used to convert the single tree photos into point cloud data,and the single tree structure parameters were extracted from the converted point cloud data.At the same time,the results of single tree structure parameters extraction based on three dimensional terrestrial laser scanning and close-range photogrammetry were compared and analyzed.Finally,based on the Visual Studio 2017 platform,single tree structure parameters extraction software based on close-range photogrammetry was designed and developed.The study results are as follows:(1)In this study,the instrument is Nikon d3400,and the values of camera calibration elements x0,y0,f,K1,K2,P1 and P2 are 11.94mm,7.74mm,18.30mm,3.54e-04,-5.83e-07,1.33e-07 and 0.by using the space resection method;and the values of calibration elements are 11.93mm,7.75mm,18.28mm,3.43E-04,-5.93e-07,2.11e-07 and 4.91e-07 by using Zhang Zhengyou Camera Calibration method.(2)The DBH,tree height,and crown width of the single tree were extracted through space forward intersection method,and the extracted values were compared with the measured data.The results show that the close-range photogrammetry method extracts the structural parameters of the single tree compared with the measured data.The average errors of DBH,tree height,and crown width were 2.1cm,0.37m,and 0.73m,respectively.The accuracy meets the needs of forest resource surveys.Correlation coefficients of DBH,tree height,and crown width of the measured values and the calculated values of photogrammetry were 0.93,0.98,and 0.91,respectively,and the correlations were high.(3)According to the written SFM algorithm program,the commonly used feature point matching algorithm was analyzed and the single tree dense point cloud was generated.Finally,the structural parameters of the single tree point cloud data were extracted.The research results show that:SIFT algorithm,SURF algorithm,and ORB algorithm performed feature point matching on the photos of trees after camera calibration.The correct number of feature points was 23,145,and 25,and the corresponding time was 18.56s,16.04 s and 1.58s,respectively.According to the point cloud data,the single tree structure parameters were extracted.The average errors of DBH,tree height and crown width were 1.79cm,0.77m and 0.79m,respectively.The correlation coefficients with measured data were 0.96,0.94,and 0.97,respectively.(4)The single tree point cloud obtained by 3D terrestrial laser scanning was of high quality,and the average errors of the DBH,tree height,and crown width parameters extracted by the 3D laser scanning method were 0.9cm,0.34m,and 0.2m,respectively.The advantages of close-range photogrammetry were that the data acquisition method is more convenient and flexible,the instrument cost is lower,and it is more conducive to multi-source data fusion.According to the close-range photogrammetry measurement,the average errors of the parameters such as breast diameter,tree height,and crown width were 1.4cm,1.07m,and 0.54m,respectively.(5)Based on the Visual Studio 2017 platform,single tree structure parameters extraction software based on close-range photogrammetry was designed and developed.This software can implement the camera calibration function and the function of measuring the three-dimensional spatial coordinates of the target point,which facilitates the investigation of trees in forest plots.