Evaluation of Manual Log Measurement Errors and Its Implications on Harvester Log Measurement Accuracy
Authors
Martin Strandgard
University of Melbourne
Abstract
Previous studies of harvester measurement accuracy assumed traditional manual log measurements were accurate and represented true log dimensions, which relies heavily on the assumption that logs are regular in shape. The objective of this study was to quantify the level of variability in manual log measurements and consider its impact on harvester calibration and accuracy assessments. Log length was measured along the top and each side and small-end diameter with callipers, a diameter tape, and a steel ruler in two radiata pine stands near Mt. Gam-bier in Southern Australia. Observed variability in manual log measurements was sufficient to affect harvester accuracy studies and calibration. Length variability on different sides of a log occurs mainly from non-square log ends. Differences due to observer were minor.Diameter measurement variability occurs mainly from the effect of stem eccentricity on each instrument, which is dependent on its number of stem contact points. Callipers have fewer contact points than a diameter tape and hence more variability. This variability was evident in comparisons between observers and instruments.
Harvester accuracy studies need to minimize manual measurement variability to identify harvester measurement errors. Length should be measured on the same side measured by the harvester. Diameter should be measured with a diameter tape in preference to callipers as they have greater stem contact and less variability.
Harvester calibration needs to minimize manual and harvester measurement variability to identify harvester measurement bias with the least number of logs to minimize the time required for these activities. In addition to the above suggestions relating to harvester accuracy study measurements, logs selected for calibration must be the most uniform in shape available to highlight harvester measurement biases.
