# Digital 3D Technologies for Humanities Research and Education: An Overview
## 3 Definitions
### 3D Modelling Technologies as a Research Object  
3.3.1. Modelling  
**Model theory**: Modelling means creating \"the (simplified) replica of an original system\", which must be \"sufficiently similar to the original system with respect to the purpose of its realization\" ([138], pp. 131; see also [139], footnote 16; [140]). In the 3D/4D modelling in humanities, this model is created \"post factum\"--after the original ([141], p. 335). Unlike architectural drafts, these models are created subsequently to the original. An established explanatory scheme of models is the general model theory. In this context, a model represents a simplified or reduced version of an original. An element of pragmatism denominates the subjective and purpose-oriented nature of a model [138]:  
* Feature of reproduction: models represent the originals that come from the world of imagination, from expressions, as well as from physical objects and symbols.
* Feature of reduction: models usually do not include all features of the original but only those considered relevant by the creator or user.
* Feature of pragmatism: models function as a surrogate of the original subjects within a certain time span, for a certain purpose (transactions).  
**Computer-based 3D modelling**: Computer-based, i.e., digital, 3D technologies have become increasingly important for sustaining conservation, research, and broad accessibility of cultural heritage as knowledge carriers, research tools, learning materials, and means of representation over the last three decades (c.f. [142; 143; 144]). Theoretical foundations and epistemological recommendations of 3D modelling of cultural heritage have been studied for a long time, e.g., within various EU projects [6; 145]; on a national level in Germany by the task group for 3D reconstruction of the DHd association [146], the Digital Art History workgroup [147], and the DFG Network for 3D reconstruction of architectural history [148], and by a large number of publications (most recently: [149; 150; 151]). An overarching consensus is that 3D modelling represents or translates either a material cultural object or an intangible cultural phenomenon into a spatial, temporal, and semantic virtual model. Main differences refer to the kind of object of assessment in terms of material and immaterial objects (e.g., usages or digital data). Furthermore, there is an essential difference between the reconstruction of objects that are no longer existent or that have never been realized (e.g., the current status of unrealized plans) and the digitization of objects that are still existent [152].  
3.3.2. Digital vs. Virtual  
There is a basic consensus that digital 3D models are created using computers and thus differ from physical reconstructions of artifacts or even paper-based reconstructions such as architectural drawings (c.f. [153]). In this context, the terms \"digital\" and \"virtual\" reconstruction are largely used interchangeably, although the underlying concepts of the digital as \"data in the form of especially binary digits\" [154] are quite different from the virtual as \"existing or occurring on computers or on the Internet\" [155]. While the digital thus describes a materiality, the concept of the virtual is based on a reference to reality in terms of content. Empirically, in the German-speaking world, the term virtual reconstruction is used more frequently, with 61.000 results compared to 13.000 results for \"digital reconstruction\" at Google search [156], while \"digital reconstruction\" predominates in English with 484.000 vs. 181.000 results. In accordance with the practice described, both terms will also be used synonymously in this article (c.f. [157]).