## 2 Materials and Methods
### Reverse Engineering Techniques and Technologies
Reverse engineering offers a multitude of applicable techniques and technologies in the field of surface digitization of physical objects, but not all of them are applicable in the field of hard-to-reach diagnostics. 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 [6]. Employing appropriate safety procedures and regulations is paramount when undertaking tasks in such confined spaces to mitigate the risk of injury or damage to the technology. When selecting and comparing specific techniques and technologies, it is imperative to consider the requirements for digitization techniques and equipment. The basic requirements for digitizing equipment include the following:  
* portability--they should be lightweight and easily portable and be able to operate in confined spaces or harsh environments;
* accuracy--the range of distances between the values obtained and the actual values;
* range--the functional range of distances between the device and the object to be digitized;
* requirements for the physical properties of the digitized objects--size, surface characteristics, shape constancy and complexity of the object, etc. ;
* repeatability--determines the extent of changes on the acquired data within several measurements of the same object by the same device and without changing the parameters;
* dynamic accuracy--the range of the number of measurements per unit time within which the specified accuracy can be achieved;
* calibration--making a comparison of the data obtained from a device relative to known values;
* volume, size, wattage and power parameters--the material and physical parameters of the equipment;
* safety--the extent to which there is a risk of harm, injury or death when working with the digitizing device;
* usability--the ability of the device to capture and measure multiple surface aspects of physical objects;
* cost--the sum of the purchase price and the operating costs over the required time horizon for the use of the device;
* output data--the method of display and representation of the acquired and retrieved data and the output format of the recorded data;
* ergonomics--design criteria for the physical and ergonomic demands of working with the device;
* robustness and durability--the ability of the equipment to withstand external influences and forces applied when working with the equipment;
* the nature, manner and extent of changes made and caused by the digitizing device to the digitized object as part of the digitization process [16]. The application of reverse engineering in the field of diagnostics of hard-to-reach places can be considered as an application of 3D digitizing technology without the use of external references and changes in the relative position of the technology and the object. Given that the real world can be conceptualized as a 3D framework defined in space, it is imperative to capture and measure real physical objects. This necessitatesthe acquisition of information regarding the distance, or depth, of the scanning device relative to the object. To address the requirements for precise measurement of features within the surface of objects and the necessity to reconstruct surface areas of objects in hard-to-reach locations, specific dedicated devices must be defined. Since the beginning of the 21 st century, these imaging and digitizing devices have been the focus of research by scientific teams worldwide. Research on 3D endoscopic devices has been particularly oriented towards medical applications in diagnostics and as an assistive technology in surgical operations. The digitization techniques employed in hard-to-reach areas can be categorized as follows:  
1. Digitization using photogrammetry: * A technique based on camera movement (Shape from Motion, SfM); * Digitization using video (Shape from Video, SfV). 2.