Log Grading Research Articles

A Comparative Literature Review of Machine Learning and Image Processing Techniques Used for Scaling and Grading of Wood Logs

This literature review assesses the efficacy of image-processing techniques and machine-learning models in computer vision for wood log grading and scaling. Four searches were conducted in four scientific databases, yielding a total of 1288 results, which were narrowed down to 33 relevant studies. The studies were categorized according to their goals, including log end grading, log side grading, individual log scaling, log pile scaling, and log segmentation. The studies were compared based on the input used, choice of model, model performance, and level of autonomy. This review found a preference for images over point cloud representations for logs and an increase in camera use over laser scanners. It identified three primary model types: classical image-processing algorithms, deep learning models, and other machine learning models. However, comparing performance across studies proved challenging due to varying goals and metrics. Deep learning models showed better performance in the log pile scaling and log segmentation goal categories. Cameras were found to have become more popular over time compared to laser scanners, possibly due to stereovision cameras taking over for laser scanners for sampling point cloud datasets. Classical image-processing algorithms were consistently used, deep learning models gained prominence in 2018, and other machine learning models were used in studies published between 2010 and 2018.

Log Grading and Knot Identification by Oblique X-Ray Scanning

Abstract The presence and location of knots within cut lumber substantially controls the physical properties and commercial value of the material. Thus, there is great practical interest in developing ways of choosing the cutting pattern for a log in a sawmill to optimize the arrangement of knots in the resulting cut lumber. X-rays can image the interior of a log to detect the arrangement of the knots; however, traditional radiography measurements are two-dimensional in character and cannot provide the needed depth information. Conversely, computed tomography (CT) can provide the required spatial details but is challenging to do in practice because of its complexity and cost. The research here aims to overcome these concerns by employing a novel “oblique” scanning technique that uses radiography to determine knot orientations with both reasonable accuracy and low cost. Image processing and detection algorithms are developed to locate and orientate the knots automatically within the scanned logs. Detection metrics of precision and recall are used to analyze the performance of the detection algorithm. Results indicate that the oblique scanning method is a viable way to detect and orientate knots within logs with both reasonable accuracy and low cost compared to existing methods. In initial tests, an average circumferential angle accuracy within 15 deg was achieved, with the detection algorithm being able to detect between 60% and 80% of the knots present within the log.

Quality traits of plantation Eucalyptus nitens logs impacting volume and value recovery of structural sawn boards

Plantations of Eucalyptus species are planted and grown worldwide for short rotations and with limited silvicultural treatments mostly to produce pulplogs for the pulp and paper industry. These resources could be used as raw material for construction timber, to support the increasing need of renewable resources from the building sector. To use fast-grown Eucalyptus logs as a source of sawn timber log grading standards are needed, which can be developed accounting for log characteristics impacting sawn timber recovery. This study aims to examine the quality of fast-grown Eucalyptus logs and relate relevant log quality traits to sawn timber characteristics. Wood quality and log characteristics of forty-nine fast-grown Eucalyptus logs and the characteristics and structural properties of 268 sawn boards milled from those logs were investigated. Significant differences were found in wood quality characteristics from logs sourced from different positions in the stem. However, sawn boards did not differ in their wood quality traits according to log position, which influenced only the amount and type of knots on the board surface and some structural properties. Moreover, log characteristics including volume, taper, log end splits and stiffness significantly impacted important board recovery traits. The results of this study show that log characteristics such as volume, taper, log end splits and stiffness should be accounted for in log grading standards seeking to grade fast-grown Eucalyptus resources for different product classes.

From Visual Grading and Dynamic Modulus of European Beech (Fagus sylvatica) Logs to Tensile Strength of Boards

The aim of the present paper is to assess the non-destructive indicating properties of Slovenian beech (Fagus sylvatica) logs and correlate them with the mechanical properties of the final product, which is boards. Beech logs were visually graded according to the standard procedure and vibrational frequencies were measured. Logs were further on sawn into boards which were also non-destructively tested in wet and dry conditions. Finally, the boards were experimentally tested in tension. Special focus was directed towards visual parameters of the beech logs and their influence on the overall quality of the output material. The longitudinal natural frequencies of the logs were studied as potential indicating properties. The results showed that a majority of the visual log grading parameters do not result in good quality timber in terms of strength and stiffness properties, and only few are decisive for the final classification. The coefficient of determination of the static MOE vs. dynamic MOE of logs was r2=0.13, whereas vs. the MOE of wet boards was r2=0.49. Using a few visual characteristics in combination with dynamic measurements of logs and of wet boards could help to increase the yield of high quality beech wood.

Curvature of Logs—Development of and Comparison between Different Calculation Approaches

In the field of electronic roundwood measurement, 3D-laser systems are becoming more and more important for the determination of log volume and quality. Especially the outer shape of the logs is of particular importance for the yield and should therefore be described in as much detail as possible. This study focuses on the parameter curvature and compares five different approaches to quantify the sweep of logs based on high-resolution 360°-scans of 269 debarked logs of the species spruce, oak and pine. We observed strong differences between the approaches, including the two variants that are currently approved in German sawmills. Due to our findings, we suggest the introduction of a method that is based on a calculated centerline through the log instead of considering the outer log contour for future German log grading.

Prediction of branch growth using quantile regression and mixed-effects models: An example with planted Larix olgensis Henry trees in Northeast China

Branch is an essential component that supports foliage for photosynthesis, and its size appears as a major determinant for log grading. Forest managers have always been facing a challenge to maximize tree increment and timber quality; hence, linking the dynamic relationship between the branch and tree growth will be beneficial for crucial stand managerial decisions (pruning, thinning, and other silvicultural practices). In this study, branch growth models were developed using 77 destructively sampled Korean larch trees (Larix olgensis Henry) from several plantations in the Northeastern area of China. A modified Mitscherlich function that includes dynamic tree height and branch height was used to predict the growth of the branch’s diameter and length. The jackknifing technique was utilized to evaluate five alternative modeling approaches: (1) fixed-effects model; (2) calibrated mixed-effects model; (3) three-quantile regression method; (4) five-quantile regression method; and (5) nine-quantile regression method. The results showed that the prediction performance of both calibrated mixed-effects and quantile regression approaches outperformed the fixed-effects model, in which the calibrated mixed-effects provided better performance than quantile regression. In addition, three sampling strategies and various number of branches (1 to 8 branches per sample tree) were used for calibrating the mixed-effect and quantile regression model. The three sampling strategies brought relatively similar prediction performance, specifically for the larger sample size. Model performance improved as the sample size increased, but gains in performance decreased gradually. Overall, a combination of Type I sampling strategy and at least five sample branches per tree was recommended as a win–win solution to minimize the required measurement cost without sacrificing the model’s predictive accuracy.

Hardwood Log Grading in the United States—Part III: An Assessment of the Current Status of Log Grading in the Hardwood Industry

Abstract This article documents how the hardwood industry, in the absence of a standardized, industry-wide log grading system, has gone about grading and scaling hardwood logs by surveying mills, primarily in the Appalachian region. In total, 135 surveys were completed by respondents and returned via mail, with only 110 of those surveys considered usable for further analysis, after a thorough review of the individual surveys. Survey responses were grouped around annual production level, with three defined levels; ≤2.5 million board feet (MMBF), >2.5 and ≤8.0 MMBF, and >8.0 MMBF. Responding mills used some variation of a log grading system based on the number of clear faces on the log and the small end diameter of the log. The most common log rule used by mills in this study was the Doyle log rule, with over 75 percent using Doyle for scaling logs. Nearly 90 percent of all mills sampled graded logs without rolling the log to examine all four sides/faces. Half of all the sawmills surveyed pay the same price per thousand board feet (MBF) for butt logs and uppers. When asked if they would support the development of a standard log grading system, about two-thirds of the respondents (66%) indicated they would indeed support a standardized system for Appalachian hardwoods. These findings can help guide the development of a set of log grading standards for buyers and sellers in the Appalachian region and other parts of the world where hardwood lumber is produced.

Hardwood Log Grading in the United States—Part II: United States Forest Service Log Grades and the Hardwood Industry

Abstract The major effort to develop hardwood log grades was undertaken by the US Department of Agriculture Forest Service (USDAFS) during the 1940s through the 1960s. While the USDAFS officially adopted the grading system for their own use in 1952, it has never taken hold in the hardwood lumber industry. This article discusses the variety of reasons that have most likely contributed to this failure of adoption of the USDAFS system by the industry, ranging from ease of use, to individual log grades covering wide ranges of log characteristics/quality, and to overlapping grades for a given set of log attributes, among others. Finally, the authors suggest developing a hardwood log grading system that embraces the de facto industry system of scaling diameter and clear faces.

Hardwood Log Grading in the United States—Part 1: A Historical Perspective

Abstract The ability to efficiently and consistently characterize the quality of hardwood sawlogs is an indispensable part of operating a hardwood sawmill. And it is equally important for buyers and sellers of hardwood logs to negotiate prices on a uniform basis of both scale and grade. While scaling of logs is relatively straightforward, assuming buyer and seller agree on a specific log rule to use (e.g., Doyle, Scriber, International), grading logs for the purposes of evaluating quality is more complex. Hardwood log grading is an essential component of any hardwood sawmill's operation and effectively sets the stage for profit or loss. Various efforts have been made to develop a standardized log grading system by both the forest products industry and the US Department of Agriculture Forest Service (USDAFS) since the beginning of the 20th century. However, even after over a century of effort, there is still no broadly accepted standard for grading hardwood logs. The purpose of this article is to document the historical evolution of hardwood log grading systems. Understanding the development of hardwood log grading systems over time can help to produce a better log grading standard in the future.

Near Infrared Spectroscopy as a Tool for In-Field Determination of Log/Biomass Quality Index in Mountain Forests

Current in-field methods for grading logs are based on visual rating scales, which are subjective, operator-dependent and time-consuming. Various wood defects such as knots, resin pockets, rot and compression wood, amongst others, affect the quality and potential usage of a log. Early detection of these defects and an adequate wood quality classification help to optimise resource use along the whole production chain. Therefore, the specific target for the development of an efficient in-field grading approach was defined within the project Integrated processing and controL systems fOr sustainable forest Production in mountain areas – SLOPE. The grading is conducted by means of automatic measurements of selected wood properties with diverse sensors, including near infrared (NIR) spectrometers. A series of studies was conducted on wooden discs using laboratory equipment and a portable NIR spectrometer. In-field measurements of standing trees and harvested logs were also performed using a portable instrument. Principal components analysis models for identification of log defects were developed using the spectra collected with both instruments. Such models will serve for the automated determination of quality indexes to be used for log grading. It is foreseen that the NIR-based quality indexes will be integrated with the expert system under development within the SLOPE project and combined with quality information derived from other sensors. The overall goal is to provide a reliable technology for automatic log quality grading in the forest industry.

Processing sawn wood from thinned, unpruned 17-year-old Eucalyptus dunnii in southern China

SummarySixty logs of 17-year-old thinned, unpruned plantation-grown Eucalyptus dunnii representing 10 trees from each of 2 provenances were obtained from a field-trial in central Guangxi Province, China, and processed in a nearby sawmill to produce dried appearance-grade sawn wood suitable for manufacture of short-length flooring. This study’s objectives included determining: interrelationships between log end-splitting and growth stress measured on standing trees and important wood behaviour during processing; relationships between log external features and sawn product recovery; the potential for improvement in processing and/or product quality with the application of a steam reconditioning treatment; and differences in product value and processing characteristics between two provenances of E. dunnii.Boards were air-dried and kiln-dried in two matched batches and one batch was subsequently given a steam reconditioning treatment. For prediction of processing characteristics, the measured displacement on standing tree stems associated with growth stress release was moderately useful for prediction of log end-splitting but not significant for any other characteristic tested, and log end-splitting was not a significant predictor of recovery or product value. Log diameter measures and sweep were the only significant predictors of recovery. Diameter was sufficiently large in some logs to meet D-grade requirements according to Australian (VicForests) log grading standards. The estimated mill door values of sawn product obtained per log cubic metre for D-grade and residual-grade logs (below VicForests sawlog specifications) were RMB 1045 and RMB 887, respectively (approximately AUD 190 and AUD 161, respectively). Steam reconditioning treatment significantly reduced cupping and increased width and thickness dimensions but the presence of severe non-drying-related defect limited the direct benefit of the treatment. There was no significant difference between provenances in product recovery, product value or log end-split severity.

국산 침엽수 원목의 경급구분 기준에 관한 연구

국산 원목의 유통체계 개선을 위해서는 원목 품질을 신뢰할 수 있는 있는 등급체계가 정착되어야 한다. 원목시장의 현실과 괴리된 원목규격의 개선을 위해 국내에서 생산되는 원목 현황과 원목이 사용되는 시장에 대한 분석이 필요하다. 이를 위해 2010년과 2011년에 국내 5개 지방산림청에서 생산 매각한 천만 본 이상의 원목자료를 수집하여 각 수종별로 경급과 재장을 분석하였다. 이를 바탕으로 원목규격의 경급과 재장구분 기준에 대한 개선방안을 모색하고자 하였다. 본 연구 주요결과를 요약하면 다음과 같다. 국산 침엽수 원목의 경급은 100~160 mm 범위의 소경재가 대부분을 차지하여 현행 원목규격의 재종구분이 현실에 비해 다소 과도하게 설정되었음을 확인할 수 있었다. 원목의 경급분포는 수종별로 서로 상이한 분포특성을 보여 수종별로 차별화된 경급기준의 필요성이 제기되었다. 국내에서 생산되는 원목의 재장이 수종마다 서로 상이하고, 제재용으로 선호되는 재장을 적극적으로 생산하지 못하는 문제점을 반영하여 재장에 관한 기준이 원목규격에 포함될 필요가 있다는 점을 확인하였다. 이러한 결과를 바탕으로 3개 수종군, 6개 재종의 새로운 침엽수 원목 구분체계를 제안하였으며, 각 등급에 적합한 지름 및 재장기준을 제시하였다. Log grading rules are essential tools to ensure the quality of logs in distribution structure. The rules should reflect the long experience and accepted usage practice in the market. A gap between the rules and market should be improved based on analysis of log qualities that produced and market demand. In this study more than ten millions logs which were produced by 5 Regional Forest Services in 2010~2011 period, were analyzed in their qualities including diameters and lengths by species. A proposal was driven to improve the current log grading rules in terms of log diameter classes and length. The followings are the summary of this study. Most of domestic softwood logs are belong to small diameter class of 100~160 mm, which imply the diameter classes of current log grading rules are immoderate. Distributions of log diameter shows distinctive patterns by species, which indicate a necessity of differentiated diameter classes by species in an improved rules. Lengths of logs in productions do not corresponding to the demands and preferences in sawmills. Therefore it is highly recommended to include log length term in an improved log grading system. Based on these findings, 6 log grading systems for 3 species groups of softwood are newly proposed to improve current log grading rules. Limits of log diameter and log length are also proposed for each log grading system.

Estimating forest biomass supply from private forest owners: A case study from Southern Germany

In this article we developed a method to estimate forest biomass availability in a situation with small-scale privately owned forests and applied it to three administrative districts in Southern Germany where the majority of owners is organised in forest owners associations. Based on gross annual increment of regional forest resources we calculated a theoretical potential of above-ground biomass from which we subtracted technical and ecological constraints, e.g. restrictions resulting from conservation needs or nutrient removal. The resulting figure was the bio-technical potential of forest biomass. We then assessed the socio-economic potential of forest biomass by considering recent timber felling rates and log grading of owners. In order to determine market potential we differentiated between self-consumption and marketed timber. We compared the calculated potential and timber utilisation patterns of forest owners, deriving the additional supply potential of forest biomass. Most of the data were obtained by a stratified random interview of 226 private forest owners organised in forest owners associations. Although observed harvest intensity was high there was still a considerable potential for increased use of forest biomass. However, willingness of owners to intensify timber harvesting and to supply fuel wood on the basis of long-term contracts is a restriction to additional mobilisation of wood.

Feasibility of Ultrasonic Log Sorting in Manufacturing Structural Lamination from Japanese Cedar Logs

Because Japanese cedar shows lower mechanical performance, glued-laminated timber (glulam) can be a better way to utilize Japanese cedar for structural purpose. However, low yield of higher grade lami- nation from log makes it difficult to design structural glulam. This study was aimed to increase the yield of higher grade lamination and provide higher efficiency of manufacturing structural lamination by ultra- sonic log sorting technology. Logs were sorted by an existing log grading rule regulated by Korea Forest Research Institute (KFRI). It was found that the KFRI log grading rule contributed to finding better logs in viewpoint of the volumetric yield and it can reduce the number of rejected lumber by visual grading. However, it could not identify better logs to produce higher-grade products. To find an appropriate log-sorting-method for structural products, log diameter and ultrasonic time of flight (TOF) for the log were considered as factors to affect mechanical performance of resulting products. However, it was found that influence of log diameter on mechanical performance of resulting products was very small. The TOF showed a possibility to sort logs by mechanical performance of resulting products even though a co- efficient of correlation was not strong (R = 0.6). In a case study, the log selection based on the ultrasonic TOF of the log increased the yield of the outermost tension lamination (E8 or better grade, KS F 3021) from 2.6% to 12.5% and reduced LTE5 (lower than E5 grade) lamination from 43.6% to 10.3%, compared with the existing KFRI log grading rule.

The impact of a strength grading process on sawmill profitability and product quality

A strength grading process, starting with log grading, was studied with respect to grading yield, impact on quality, and economic efficiency when visual grades according to Nordic grading rules were used for alternate product comparison. Pine (Pinus sylvestris) and spruce (Picea abies) logs and boards were graded with several varieties of commercial grading and strength-grading equipment. The boards were destructively tested, and the European grade-determining properties strength, stiffness, and density were measured. Models for these were made by partial least squares and validated. A method for the derivation of settings for multiple indicating properties, which increased yield in some cases, was proposed and evaluated. Grading to grade combinations of C40, C30, and C18 was done. The impact of visual override based on deformations was also studied. A simplified economic and sensitivity analysis was done. The outcome was that log grading can be used for strength grading with good economic and quality results. Strength pregrading on logs improves sawmill economy, depending on the species and market situation. Drying quality greatly influences the yield through visual override grading on deformations. Market prices of high grades (>C30) must improve in order to stimulate supply, as it is more economical to produce lower grades.

Stress wave sorting of red maple logs for structural quality

Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) of logs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those for which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation techniques to sort red maple logs for the potential quality of lumber obtained from them. Ninety-five red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into cants and lumber. The same procedure was used to obtain stress wave times in the cants and lumber. The lumber specimens were then dried and graded using a transverse vibration technique. The results of this study showed that good relationships existed between stress wave times measured in logs, cants, and the lumber produced from the logs. It was found that log stress wave grades have positive relationships with the lumber grades. Logs with high stress wave grades produced high-grade lumber. These findings indicate that the longitudinal stress wave technique has potential in sorting logs and cants for the production of high MOE products.

Automatic grading of sawlogs: A comparison between X-ray scanning, optical three-dimensional scanning and combinations of both methods

As sawmills become increasingly efficient, the importance of focusing on value recovery becomes obvious. To maximize value recovery, sawmills require the ability to sort logs according to quality. This study compares four different combinations of three-dimensional (3D) and X-ray scanning that can be used to grade logs automatically. The study was based on 135 Scots pine (Pinus sylvestris L.) logs that had been scanned with both a 3D scanner and an X-ray scanner with two X-ray sources. The percentage of boards with correct grade sawn from automatically graded logs varied from 57% when using only 3D scanning to 66% when using a combination of 3D scanning and X-ray scanning in two directions. The highest possible result, with ideal log grading, was 81%. The result also shows that the combination of a 3D scanner and one X-ray direction results in higher accuracy than a scanner based on two X-ray directions.

Modification of log grading and log segregation strategies for low-quality logs from the East Gippsland FMA of Victoria

Summary The potential for segregating higher-quality residual logs at sawmills for the production of sawn timber was investigated in low-quality eucalypt logs from mixed-species forests in the East Gippsland Forest Management Area of Victoria, Australia. Studies were conducted on long-length bush logs that were graded in the forest and were below existing minimum specifications for sawlogs (lower quality than A, B, C or D-grade sawlog). Following cross-cutting to sawlog length at the sawmills, 15% of logs (82 logs) were found to meet existing sawlog grades, probably because internal defect visible on the ends of logs was less severe than on the full-length bush logs. Conventional sawing systems and strategies were applied to assess the timber quality from the remaining 85% of the cross-cut logs (449 logs). Multiple regression analysis was used to develop a grading method that could be applied at the sawmill to produce two new residual log grades (Residual grades 1 and 2). After applying the grading method, Residual grade 1 logs were found to have recoveries similar to those of E-grade logs that are currently milled with higher-quality sawlogs. However, a greater percentage of logs could be selected with the new method. While it was found to be ineffective in low-elevation mixed-species forests where selective logging left a high proportion of large defective trees, the grading method can have broad application across all the other forest types examined. There are four main differences to the existing log criteria: (i) mean end defect rather than worst-end defect is used as an indicator of log quality (ii) mean minimum diameter of logs is 25 cm with no small-end restrictions, (iii) the definition of a clear quarter is different that is, existing rules allow clear quarters to have a defect or combination of defects that have a width no greater than one- third of the surface width of the quarter on which they occur a clear quarter in the new criteria has no visible defect apart from small epicormics and (iv) logs with mean diameter <40 cm and end defect >40% are permitted to have four defective quarters.

Acoustic segregation of Australian-grown Pinus radiata logs for structural board production

Summary The wood quality of sawlogs is highly variable and poorly reflected by log physical dimensions. Current log grading rules for structural timber, based purely on physical appearance, result in a significant loss of value to growers and processors. Growers and processors both require tools that are able to rapidly sort logs to yield timber of a uniform quality. Ninety-two radiata pine (Pinus radiata) logs harvested from Green Hills State Forest, NSW, were measured at the Hyne and Son sawmill at Tumbarumba, NSW. Two non-destructive longitudinal stress wave acoustic devices, a FAKOPP single-pass transit-time tool and a Wood Spec resonance tool, were used to characterise the logs. The sampled logs were sorted into three sound speed classes: slow (<3.5 km s−1), medium (3.5–3.7 km s−1) and fast (>3.7 km s−1). The relationship between measurements of acoustic velocity in logs and the stiffness of the boards milled from the tested logs was established. The boards recovered from logs sorted into the fast sound class had a mean stiffness of 10.5 GPa. The boards recovered from the logs segregated in the medium and slow sound classes had mean stiffnesses of 9.3 GPa and 8.9 GPa, respectively. The acoustic segregation patterns were similar for each of the acoustic tools tested, with the coefficient of variation of repeated measurements with WoodSpec being 2.2% lower than with the FAKOPP, suggesting that the WoodSpec tool was more precise. This study indicates that acoustic measurement of wood stiffness in the field and in the mill may improve value recovery.

Dichotomous Keys for Scaling and Grading Merchantable Quality Sawlogs

Abstract This study documented and field-tested a simplified version of the Westside Grading Guidelines as published in the Official Rules Handbook by the Northwest Log Rules Advisory Group. A four-step dichotomous key was documented and field-tested to determine merchantable vs. nonmerchantable logs. The study also documented and field-tested an individual seven-step dichotomous log grading key for evaluating second-growth Douglas-fir (Pseudotsuga menziesii), Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), and grand fir (Abies grandis) as derived from the Rules For Grading Logs section of the Official Rules Handbook. Results were compared with certified scalers employed by Yamhill Log Scaling &amp; Grading Bureau and Columbia River Log Scaling &amp; Grading Bureau. Eighty-four individuals measured the length, scaling diameter, determined merchantability versus nonmerchantability and assigned log grade for 440 logs. Results showed participants in the study correctly measuring log length 99% of time, scaling diameters were recorded correctly at an 89% rate, and merchantability and log grade at 98 and 97%, respectively. West. J. Appl. For. 18(4):250–258.