Accuracy and Suitability of Photogrammetry and Lidar-Based Methods To Estimate The Log Volume

Estimation of log volume is still carried out in several countries using analogue instruments and traditional methods. During the purchasing phase, the accuracy of the log volume measurement process plays a key role, as the cost of purchasing this raw material represents between 60% and 85% of the final production cost. Miscalculations in volume estimation can lead to dramatic losses for the purchasing companies or forest owners. In several European countries, logs destined for sawmills because of their high quality, long lengths and high midpoint diameters are transported to landings or forest roads sides to be measured by the staff of the involved stakeholders. At this point, the volume of each log is estimated based on the diameters and length measured, using analogue tools and formulas traditionally used in each region, such as the Huber or Smalian formulas. Recent studies have demonstrated the high accuracy of lidar-based methods for estimating the volume of logs as their volume was measured using a xylometer which is deemed as the most accurate method for that purpose. In addition, these developed lidar-based methods bring further advantages that lead to the optimisation of the measurement process, such as transparency increase, lower time consumption and comfort for the staff responsible for carrying out the measurements in the forest. The aim of this study is to compare the accuracy and suitability of selected recently developed methods for estimating the volume of logs in the forest. Lidar and photogrammetry-based methods were selected for this study, being collected the data using 1) UAVs, 2) iPhone with ViDoc RTK device, 3) GeoSLAM ZEB HORIZON and 4) GoPro Hero11 camera supported in a Zhiyun Crane M3 gimbal. For this study, 87 oak logs (Quercus robur L.) were prepared and measured in the forest district located in Chorin (Brandenburg, Germany). Their length ranged from 3.34m to 11.82m and their midpoint diameter from 47cm to 94cm. The accuracy of the selected methods will be evaluated based on the volume estimated using traditional methods. Specifically, Root-Mean-Square Error and Mean Bias Error will be calculated to compare the results provided by each method and evaluate the accuracy. The suitability of each method will be assessed based on the time required to estimate the volume of each log and the reliability of the obtained results.