Automatic Estimation of Tree Position and Stem Diameter Using a Moving Terrestrial Laser Scanner

Abstract

Airborne laser scanning is now widely used for forest inventories. An essential part of inventory is a collection of field reference data including measurements of tree stem diameter at breast height (DBH). Traditionally this is acquired through manual measurements. The recent development of terrestrial laser scanning (TLS) systems in terms of capacity and weight have made these systems attractive tools for extracting DBH. Multiple TLS scans are often merged into a single point cloud before the information extraction. This technique requires good position and orientation accuracy for each scan location. In this study, we propose a novel method that can operate under a relatively coarse positioning and orientation solution. The method divides the laser measurements into limited time intervals determined by the laser scan rotation. Tree positions and DBH are then automatically extracted from each laser scan rotation. To improve tree identification, the estimated center points are subsequently processed by an iterative closest point algorithm. In a small reference data set from a single field plot consisting of 18 trees, it was found that 14 were automatically identified by this method. The estimated DBH had a mean differences of 0.9 cm and a root mean squared error of 1.5 cm. The proposed method enables fast and efficient data acquisition and a 250 m 2 field plot was measured within 30 s.

Comparing Three Different Ground Based Laser Scanning Methods for Tree Stem Detection

“…A BPLS was developed as an extension of the scanner presented in Oveland et al [8]. The BPLS was an in-house-build.…”

“…Oveland et al [8] have developed and described a MLS-based system for acquisition of single tree positions and diameters at forest field plots. This system used data from an airborne laser scanning to determine the ground level.…”

“…This can be utilized, and in combination with information about the orientations and movements, it can be used to retain the current position in areas with poorer GNSS conditions. Use of IMU in combination with GNSS in forests was applied, e.g., by Kaartinen et al [26], Forsman et al [17] and Oveland et al [8], to handle information about the orientations and movements. In the current study, tightly coupled GNSS-IMU post processing software called TerraPos [27] was used to obtain the position throughout the data collections.…”

“…Rather than scanning from fixed positions, such systems will continuously record data while the instrument is carried through the forest field plot. The instrument can be carried by a human [8,15,16], or mounted on a vehicle [17,18].…”

“…TLS produces three-dimensional data in the form of dense point clouds, and by processing and analyzing these point clouds several biophysical characteristics related to the forest and the trees can be extracted. Methods have been developed for automatic identification of tree stems and extraction of stem diameters [6][7][8][9][10][11]. Others have developed methods for more detailed reconstruction of the tree stem and branch structure [12].…”