# Detection of Pest Feeding Traces on Industrial Wood Surfaces with 3D Imaging
## 1 Introduction
One study [42] indicates an increase  
Figure 1: Examples of pest-caused holes on the wood surface analysed using a metrological glass scale with a millimetre grid. in production efficiency of 23% for jack pine and 15% for white spruce. The return on investment is estimated to be around eight years for medium sawmills [43]. Operator safety is also an essential consideration for a system based on the CT method [44]. To date, applications of laser triangulation imaging in the timber industry have been limited to imaging the outside of the log before sawing [45]. [PERSON] et al. [46] compare the methods presented in terms of system cost and capability. The laser triangulation method (LTM) cannot image the interior of the material. It is also possible to propose a hybrid system combining 2D and 3D analysis capabilities [47]. According to an analysis of the literature, each method has certain drawbacks. The plane images obtained using visible light are susceptible to changes in intensity due to changes in the wood colour, its moisture content, and differences in surface treatment. Thermographic imaging suffers from low resolution and long exposure times. Furthermore, computed tomography and ultrasound imaging have significantly higher costs and require safety-critical working conditions. The research described in this paper aims to prepare an automated system for detecting pest-feeding traces visible on the surface of wood in the form of wormholes for use in industrial conditions. It was assumed that the system should be able to detect wormholes on material transported at speeds of up to 1.5 m/s and that the inspection system should detect holes with a minimum diameter of 1 mm randomly distributed on the surface of the wood. However, the latter proved to be a redundant assumption because, during the preliminary research, holes with a minimum diameter of approximately 1.8 mm were detected on the wood surface (Figure 1). Nevertheless, this approach allows for the imaging of wormholes that are not closed during the wood surface treatment. It was also assumed that the imaging method and its parameters would be selected so that the system would not be sensitive to changes in the colour and moisture content of the wood. On the surface of wood with a high moisture content, the image of the wormholes should be similar to that of the regular material. A similar phenomenon occurs with wood that is darker in colour or wormholes that form close to the annual rings. Due to the industrial purpose of the system, it was assumed that the image acquisition and analysis should be at most 1 s. During this time, all wormholes visible on the wood surface should be identified and highlighted. Quality assessment requires selecting the imaging method, resolution, and frequency [48]. These parameters should ensure that an image is produced that shows the wormholes as the material moves. The hole should be visible so that its diameter can be determined. Algorithms should then be proposed to identify the holes and their locations and to classify the material according to accepted quality criteria applicable to the production plant. A triangulation method using line laser illumination was chosen for imaging the wood surface in this study. The technique produces a 3D image of the surface of the object. The scanning is carried out optically and is contactless so that the object remains intact after its evaluation. The technology is widely used in the woodworking industry and other industries. [PERSON] [49] proposed a method for the acquisition and analysis of 3D morphologies of coarse aggregates based on laser scanning. Other work [50] indicates the possibility of flatness deviation measurements of the aluminium body. The time needed for full-image analysis is up to 1000 ms. Another study proposed a configuration with two lasers of different wavelengths [51]. The authors evaluated the method in the case of printed elements and mushrooms. [PERSON] [52] developed a rail-track inspection system based on the LTM.