## 3 Method and Materials  
### Structured-Light 3D Scanning  
Structured light scanners are active devices because they emit light beams from their own source. Scanners of this type project an appropriate pattern of light (a series of fringes with different and, in addition, time-varying widths, a dot matrix or other shape) onto the digitised object. Thanks to this, it is possible to accurately capture the geometric shape of the analysed surface. A light beam with a defined pattern is produced by built-in LCD projectors or other sources. In existing structures, white light is most often used, but also blue or green. These devices also have two or more cameras, as well as detectors that analyse and calculate the distance of surface points in the field of view. Thus the transferred object to the digital world has real dimensions. It should be emphasised, however, that scanners of this type are very sensitive to lighting conditions. All shadows on the real object are mapped onto the generated digital 3D model. For this reason, using them outside can be quite problematic. These scanners typically do not (or even not at all) capture data from black, shiny or transparent surfaces. In such situations the solution used is a matted surface by covering them with a special spray with powder before scanning, which is not allowed when digitising historic artefacts due to their protection. Scanners of this design are characterised by high speed of data acquisition and accuracy of measurements up to several micrometers. These scanners work at short distances (usually 15-40 cm) and, importantly, some structures (e.g., by Artec) can be hand-held, which significantly increases the efficiency of work when using them. There are also known solutions that always have to be mounted on tripods (e.g., RangeVision Neo devices).  
Currently, there are many 3D SLS design solutions on the market. Spider and Eva model scanners (Artec, Luksemburg, Luksemburg) are frequently used devices in museum conditions. The fact that these models belong to one manufacturer means that they have common software and the same configuration process. Their main advantage is the comfort of use, because they are light and small, and thus allow a full range of motion during scanning. The advantages also include precise texture and colour reproduction as well as high resolution of the obtained point clouds. This allows for precise examination of objects of various sizes and varied surfaces. The Artec Eva model is better suited for scanning simple geometries, while the Artec Spider model for objects with a complex structure and intricate patterns. It is important that they do not require the use of positioning markers while working, which makes them ideal for scanning museum artefacts. There is also no need to calibrate them before each scanning process, which significantly simplifies and speeds up the work. The specifications of both scanners are presented in Table 1.  
These scanners are an effective solution for safe and non-contact digitisation of museum collections. The light with which the measurements are made is neutral for them, so they can also be used to scan very delicate, old and valuable objects. Of course, there are other solutions for devices of this class. Study [40] presents data of the devices compared and parameters of the 3D models obtained.