Log end face image and stem tapering indicate maximum bow height on Norway spruce bottom logs
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ORIGINAL PAPER
Log end face image and stem tapering indicate maximum bow height on Norway spruce bottom logs Antti Raatevaara1,2 · Heikki Korpunen3 · Harri Mäkinen4 · Jori Uusitalo1 Received: 3 May 2020 / Revised: 28 July 2020 / Accepted: 6 August 2020 © The Author(s) 2020
Abstract In cut-to-length logging, the harvester operator adjusts the bucking in accordance with visible defects on processed stems. Some of the defects, such as a sweep on the bottom of the stem, decrease the yield and quality of sawn products and are difficult for the operator to notice. Detecting the defects with improved sensors would support the operator in his qualitative decision-making and increase value recovery of logging. Predicting the maximum bow height of the bottom log in Norway spruce (Picea abies (L.) Karst.) with log end face image and stem taper was investigated with two modelling approaches. A total of 101 stems were selected from five clear-cut stands in southern Finland. The stems were crosscut and taper measured, and the butt ends of the bottom logs were photographed. The stem diameter, out-of-roundness, and pith eccentricity were measured from the images while the max. bow height was measured by a 3D log scanner at a sawmill. The bottom logs with an eccentric pith had higher max. bow height. In addition, a highly conical bottom part of the stem was more common on the bottom logs with a large max. bow height. Applying both log end face image and stem taper measurements gave the best model fit and detection accuracy (76%) for bottom logs with a large max. bow height. The results indicate that the log end face image and stem taper measurements can be utilised to aid harvester operator in deciding an optimised length for logs according to the bow height. Keywords Norway spruce · Bow height · Sweep · Log end face · Pith eccentricity · Stem taper
Introduction
Communicated by Martina Meincken. * Antti Raatevaara [email protected] Heikki Korpunen [email protected] Harri Mäkinen [email protected] Jori Uusitalo [email protected] 1
Department of Forest Sciences, University of Helsinki, Latokartanonkaari 7, 00014 Helsinki, Finland
2
Natural Resources Institute Finland, Latokartanonkaari 9, 00790 Helsinki, Finland
3
Natural Resources Institute Finland, Korkeakoulunkatu 7, 33720 Tampere, Finland
4
Natural Resources Institute Finland, Tietotie 2, 02150 Espoo, Finland
Bucking of tree stems bounds the forest resources to meet the quality criteria of end users. It is performed in cut-tolength harvesters based on price and demand matrices, which define the desired log dimensions and their values, while defects are observed by the operator. However, it is difficult for the operator to notice defects related to stem form, such as sweep. There is a great demand for sensors that would measure properties of the processed stems and improve operator support in making qualitative assessments on the fly. Increased information from the properties of raw material could be used to further enhance
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