# Digital 3D Technologies for Humanities Research and Education: An Overview
## 3 Definitions
### 3D Modelling Technologies as a Research Object
#### 3.3.3 Reconstruction vs. Digitalization  
**3D digitization or reality-based modelling**: 3D Digitization or reality-based modelling [84,158] stands for \"the process of converting something to digital form\". [159]. Digitization describes the technological transfer of a real object to a digital asset. For this purpose, various data acquisition technologies are used (c.f. [157,160,161]). For tangible objects, a main distinction is between light-dependent and light-independent methods [162]. Light-dependent systems emit light to retrieve information about the 3D surface. This comprises active approaches where coded light is projected onto a surface (e.g., white-light scanners using structured light to determine the surface shape and laser scanning sending laser beams at a varying angle to determine 3D surface points using the time-of-flight principle [81,163]) and passive methods using imagery as videos or photos [164] without specifically coded light [162,165]. The outcome is a dense 3D point cloud, which is then processed into a meshed surface [166]. Methods not using visible light comprise a large variety of tomographic methods such as CT scanning to model the internal structures or volume of the object [163]. A taxonomy of the quality of 3D digitization of tangible heritage was recently developed within the EU VIGIE study [79]. According to this study, the main attributes describing a digitized object are geometry, composition (as material information), and production (as the model acquisition process) (c.f. [167]). **3D reconstruction or virtual-based modelling**: Whereas digitization refers to the technological conversion of an object into a digital representation, a digital reconstruction or virtual-based modelling process [84] requires the human interpretation of data to create a hypothesis of a past object (c.f. [152,168,169,170]). The model is then mostly created on the computer using manually controlled computer graphic modelling software originating from construction and engineering in the case of computer-aided design (CAD), or from design and creative industries by computer-generated imaging and graphics software (CGI). Since those processes are highly labor-intensive, approaches to reduce the required work include generative or parametric modelling (predefining objects by rulesets with changeable parameters) or semiautomated modelling (e.g., from historical imagery) [152,169]. **3D meshing and texturing**: Both, 3D digitization and reconstruction lead to 3D models representing surfaces and/or volumes of a tangible heritage object. Since modelling approaches of volumetric models vary significantly depending on the methods used [171], the 3D surface representation can be based on points (point clouds), triangular meshes (vertices, edges, faces), curves and shapes (generative approaches as NURBS), geometric solids (constructive solid geometry, CSG), and boundary representations (B-reps) (cited according to [163]). Besides the geometry features of a 3D model, its radiometric parameters and materiality representation are relevant [85]. For surfaces, a main distinction is between synthetically generated _procedural textures and reality-based textures_. Related to the latter category, another distinction is between the acquisition of material properties [172] and digital visualization [173]. **Simulation:** Simulation refers to a \"procedure for reproducing a system with its dynamic processes in a model that can be experimented with in order to arrive at findings that can be transferred to reality\" (translated from [174], p. 1; a definition from humanities: [175], see also [176]). Law and Kelton [177] distinguish three types of simulation depending on the models used:  
* Static vs. dynamic: A static simulation provides a replica of a system at a specific point in time. A dynamic simulation represents a system whose states, attributes, processes, etc. are time-dependently variable [178]. * Discrete (countable) vs. continuously (measurable) values.