A model for the position and ring eccentricity in transverse sections of Norway spruce logs

The objective of this work was to model the pith position and the ring ecce ntricity within the cross-sections when the external shape of the logs is m easured with an optical Multipoint scanner (or '3D optical scanner'). This work was carried out on 285 sampled discs originating from 36 trees. At a f irst stage, it was found that the external share measurements were sufficie nt for an estimation of the disc eccentricity (distance between the pith an d the disc geometric center) but not for locating precisely the pith within the cross-sections. At a second stage, we have shown that the ring eccentr icity was increasing with the ring age counted from the pith. A model was p roposed to describe these variations. The comparison between the measured r ing eccentricity and the model-predicted one was satisfactory (r(2) = 0.677 , when the disc eccentricity is estimated by the model) and excellent (r(2) = 0.923), when the disc eccentricity is measured and integrated as input i n the model. This result motivates further studies concerning the automatic detection of the pith position by image analysis.