Development and Validation of a Photo-Based Measurement System to Calculate the Debarking Percentages of Processed Logs

Abstract

Within a research project investigating the applicability and performance of modified harvesting heads used during the debarking of coniferous tree species, the actual debarking percentage of processed logs needed to be evaluated. Therefore, a computer-based photo-optical measurement system (Stemsurf) designed to assess the debarking percentage recorded in the field was developed, tested under laboratory conditions, and applied in live field operations. In total, 1720 processed logs of coniferous species from modified harvesting heads were recorded and analyzed within Stemsurf. With a single log image as the input, the overall debarking percentage was calculated by further estimating the un-displayed part of the log surface by defining polygons representing the differently debarked areas of the log surface. To assess the precision and bias of the developed measurement system, 480 images were captured under laboratory conditions on an artificial log with defined surface polygons. Within the laboratory test, the standard deviation of average debarking percentages remained within a 4% variation. A positive bias of 6.7% was caused by distortion and perspective effects. This resulted in an average underestimation of 1.1% for the summer debarking percentages gathered from field operations. The software generally performed as anticipated through field and lab testing and offered a suitable alternative of assessing stem debarking percentage, a task that should increase in importance as more operations are targeting debarked products.

In-stand debarking with the use of modified harvesting heads: a potential solution for key challenges in European forestry

“…The measurement system was based on a photo-optical evaluation system that used one picture of every stem and estimated the rest of the stem surface. Tests showed that the average debarking percentage is very precise over a larger sample size (n > 20) (Heppelmann et al 2019b). However, the downside was that the individual values have only limited significance, since in the photo-optical analysis only a maximum of 50% of the total surface was displayed and actually measured.…”

“…Logs varied between 2.4 and 5.4 m in length, and diameters ranged from 8.0 to 54.7 cm. Following these measurements, a single picture per log (broadside) was taken with a reflex camera mounted on a tripod set at a height of 1.50 m above ground (Heppelmann et al 2019b). The camera was moved after every picture and relocated to the next log.…”

“…Once in the office, debarking percentage was evaluated with a computer software solution that was developed within the scope of the project (Stemsurf). With the digital pictures of logs as input, the software used polygons to define debarked areas and calculated the total debarking percentage for the log using the additional measured physical values (diameter and length) (Heppelmann et al 2019b). The polygons were delineated manually and defined either as wood, bark, inner bark, covered, or not measurable.…”

“…Due to distortion, pixels located toward both extremities and the upper and lower sides of the stem were also subjected to a factor as the pixel described more surface than a pixel located in the middle of the log. Therefore, the curvature and distortion were also taken into account by considering this effect within the Stemsurf algorithm (Heppelmann et al 2019b). The debarking percentage was calculated as (Eq.…”

Efficiency of Harvester with the Debarking Head at Logging in Spruce Stands Affected by Bark Beetle Outbreak

“…The modification of feed rollers is represented by the replacement of spikes or horizontal roller ribs with spiralized ribs [22,24]. Thanks to this improvement, the stem rotates around its longitudinal axis while being processed, thus helping the debarking knives remove bark more perfectly from the entire stem surface [25]. Furthermore, if these modified feed rollers have an added wider and less aggressive length measuring wheel, we can describe another category whose representative is John Deere with the H480C head [23].…”