## 2 Materials and Methods
### Technical Diagnostics in Hard-to-Reach Places  
Hard-to-reach places within the industrial environment are not clearly defined. Hard-to-reach places can be considered as areas where it is not possible to perform the required activities and to use conventional technologies used in a typical environment, and the definition of \"hard to reach\" can be approached from several perspectives. In each industry sector, hard-to-reach places may be different and industry-specific. In terms of the environment in which the technology is used, hard-to-reach places can be divided into the following:  
1. Inaccessible environments;
2. Underwater environments;
3. Inaccessible environments in architecture and inspection of buildings and structures;
4. Underground environments;
5. Hard-to-reach environments with dimensionally restricted access openings;
6. Environments with limited working space and tight environments;
7. Confined working environments;
8. Areas with small objects and angled surfaces;
9. Environments with access that is legally restricted;
10. Hazardous environments. Hard-to-reach places can also include environments with harmful influences, hazardous environments, and environments in excessively low and high temperatures. In industrial and manufacturing environments, in particular, environments with dimensionally restricted access openings, environments with limited working space, and enclosed working environments can be considered as hard-to-reach places. Technical diagnostics is an engineering discipline dealing with methods and means of detecting technical conditions. The aim of technical diagnostics is to detect hidden faults, fault areas, and their extent and causes. It seeks to increase reliability, reduce operating costs, and ensure safe operation. Diagnostics is a set of processes carried out in a well-defined sequence in order to evaluate the technical condition of the object under examination. For objects examined by technical diagnostics, it must be possible to identify the functional and fault conditions. In the context of technical documentation, three activities can be applied to the object of technical condition investigation: to diagnose the current state of the technical condition (diagnosis), to predict the future state of the technical condition (prognosis), and to determine the history of the condition (genesis) [15]. Technical diagnostics in the current state of the art can be divided into the following:  
1. Vibrodiagnostics--diagnostics based on vibration testing;
2. Thermodiagnostics--diagnostics based on temperature testing;
3. Acoustic or noise diagnostics;
4. Boroscopic, endoscopic, and videoscopic diagnostics--inspection of the interior of machinery and equipment;
5. Pressure diagnostics;
6. Diagnostics of shape deformations;
7. Water level diagnostics;
8. Fluid flow diagnostics;
9. Heat and energy diagnostics;
10. Concentration diagnostics;
11. Gas emission diagnostics;
12. Defectoscopy diagnostics--defectoscopy;
13. Tribodiagnostics--investigation of oil lubricity and wear of machine parts;
14. Diagnostics based on modal analysis of dynamic behaviour;
15. Electrical diagnostics--electrodiagnostics;
16. Multiparametric diagnostics using several diagnostic methods [15]. Due to the fact that the field of digitizing physical objects within reverse engineering is based on the acquisition of coordinate points of the surface areas of these objects, only diagnostic techniques related to the investigation of the shape areas of the surface of physical objects can be considered relevant when applying reverse engineering techniques to hard-to-reach places. For this reason, boroscopic, endoscopic, and videoscopic diagnostics, shape deformation diagnostics, defectoscopic diagnostics, and multiparametric diagnostics can be considered among the relevant diagnostic techniques in the field of hard-to-reach places. These diagnostic techniques belong to the field of non-destructive testing (NDT) [16].