## 3 Results
### Systematic Evaluation of the Identified Literature
#### 3.4.3 Virtual Model Creation  
A total of 14.29% of the identified papers were assigned to the cluster \"virtual model creation\". As highlighted in the discussion on DT definitions, the VM is an essential part of a DT. To speed up the creation of this model, several frameworks and approaches can be found within the analyzed papers. [PERSON] et al. conducted a literature review of 41 articles to identify the different activities involved in in-house logistics processes. These can be differentiated between distribution facilities and production facilities. The activities receiving, storing, order-picking, cross-docking, and shipping are identified within distribution facilities. For production facilities, the distribution facility is described as a sub-model of the system. The activities were divided into receiving, storing, order picking, line feeding, and line-side presentation. Real entities were matched with predefined simulation objects to create a simulation model. Human pickers were matched with workers, cobot pickers and transporters were matched with vehicles, storage and product locations with combiners, products as well as bins and orders with entities. To evaluate this framework, two offline simulation models were created and validated [30]. [PERSON] et al. present several generic building blocks for creating the VM of a DT for discrete manufacturing systems based on DES. It is differentiated between elements and relationships: man, machine, material, method, and environment are described as elements, and the production relationship describes the hierarchical structure whereby the logistics relationship covers the network structure of the system. To verify the concept, it was implemented in a production system for aerospace components. The VM within the DT is mainly used for real-time production monitoring and production schedule verification. It is mentioned that no formal verification and validation of the VM has been performed [32]. Another approach was taken by [PERSON] et al. to create a partially automated simulation model. First, spatial parameters such as position and geometries are obtained from 3D scanning methods, e.g., photogrammetry or LIDAR scans. The scans are then matched with additional information about the objects from a reference database of computer-aided design models. Further, company-specific information must be added to the simulation model, which is obtained through surveys. Defined parameter groups are enhanced with specific data from material flow planning, investment planning, and capacity planning. Computer-Aided Design (CAD) data and data from the scanning process are transferred via XML directly into the DES environment used. This approach is intended to speed up the generation time of a simulation model. The work focuses on the generation of a virtual offline model, but other dimensions and requirements of a Digital Twin are not addressed [21]. It is shown that the virtual representation of humans plays an important role for DTs of logistics systems. Digital human simulations represent workplaces and humans, as well as interactions between them. Most digital human models include a set of predefined functionalities and capabilities so that humans can be modeled like technical equipment. To mirror humans more accurately in VMs, [PERSON] et al. suggest a different approach. Here, human motions are captured using low-cost optical, force, and torque sensors. Modeling parameters, motions, and constraints of a specific human can be captured and integrated into the simulation. A case study for pick and place processes in a warehouse is presented, where motions and physical characteristics of three operators were recorded. After the record, the simulation designs a desired workspace and assembly steps in terms of ergonomics and cycle motion times [44].