Method to estimate the medullar rays angle in pieces of wood based on tree-ring structure: application to planks of Quercus petraea

Estimating wood parameters employing non-destructive methods has been widely studied in recent years. The choice of wood used to build wine ageing barrels (cooperage) is strongly influenced by wood anatomy and specifically by the orientation of medullar rays among other aspects. In this article, a method based on the regularities of the tree-ring structure to estimate the medullar ray angle of the cross section of a piece of wood is proposed. This angle shows the direction of the best linear path to evaluate several tree-ring features and could be employed to automate tasks, such as introducing an analysis path or rotating the image prior to the analysis, which some dendro analysis methods require. A dataset of 26,992 synthetic images and 110 real oak wood images was used to validate the approach. The medullar ray angle of each image considered was measured manually and estimated using the method proposed here, which employs the fast Fourier transform (FFT) to take advantage of the tree-ring structure regularities and find the direction angle of the best linear path to evaluate several tree-ring features. The results obtained demonstrate a mean squared error of 0.29° and 8.19° and a mean absolute error of 0.19° and a 5.91° for the synthetic and oak wood images, respectively. These data suggest the suitability of the proposed method as part of an automated system to inspect and analyse the growth rings in oak wood planks.