# A Digitally Enhanced Ethnography for Craft Action and Process Understanding
## 2 Related Work
### Digitization of Endurants
#### 2.1.2 Three-Dimensional Digitization  
The 3D digitization of endurants regards structures of a wide variance of spatial scales, in indoor and outdoor environments. The choice of the 3D scanning modality depends on the size, material, and environment type. In some cases, researchers may employ multiple scanning modalities, each operational on a specific scale. For example, rooms and outdoor areas require combining terrestrial laser scanning and aerial photogrammetry. For smaller artifacts, photogrammetric reconstruction and active illumination sensors are simple and widely accessible. Comprehensive reviews of 3D digitization technologies can be found in [17; 28; 29; 30; 31].  
The field of 3D digitization encompasses a variety of techniques and modalities, each with its own set of distinct characteristics. Three-dimensional digitization, or 3D scanning, has attracted a growing interest in documenting structured scenes. Several 3D scanning modalities have been developed, distinguished by whether they require contact with the scanned surfaces and objects. Non-contact scanning modalities are more widely employed, as they use light as the operating principle of the sensor. They can be further classified according to the sensor type, that is, into passive or active illumination systems. Active sensors emit their electromagnetic energy for surface detection, while passive sensors utilize ambient light.  
The most adopted and robust principles for the digitization of tangible CH are time-of-flight or laser scanning, e.g., [32]; structured light, e.g., [33]; and photogrammetry, e.g., [34]. A range of products employs these principles in variations, including digitization over time [35]. In photogrammetry, terrestrial and aerial photogrammetry often differ, with the latter using the Global Positioning System (GPS) coordinates of a drone sensor to assist reconstruction. Combinations of these principles are found in off-the-shelf devices, such as handheld scanners that combine trinocular photogrammetry with active illumination.  
The available technologies vary based on resolution, accuracy, range, sampling rate, cost, operating conditions, skill requirements, the purpose of documentation, the material of the scanned object, weight, and ease of transport. Photogrammetric techniques provide more photorealistic texture than time-of-flight modalities but are less accurate. When accuracy is paramount, close access to the scanned object is required. If this is impossible or impractical, aerial scans can be used. In this case, though, time-of-flight techniques provide less accurate results if the sensor is airborne and thus not static. Hence, sensor sampling rate and scan duration are relevant, as a time-of-flight scans last much longer than the acquisition of photogrammetry images.  
However, not all types of materials can be digitized using these methods. Artifacts made from challenging materials exist and require specific treatment. Challenging materials exhibit specular, shiny, transparent, and translucent properties because conventional 3D reconstruction methods operate only for approximately Lambertian (matte) surfaces. Some examples are glass artifacts and shiny metals. Their digitization requires novel techniques. We have developed two techniques for transparent [36] and shiny materials. The digitization of objects and workspaces follows the guidelines established in [37].  
When it is difficult to perform digitization using scanning methods, modeling is possible, which refers to the computer-aided design of 3D tool models. Also, sometimes, models of tools are already available. A combination of methods is usually recommended depending on the digitization target, composition, and environment, and purpose for which the acquired digital media will be used.