## 1 Introduction  
Nowadays, more than an amusement platform, augmented reality (AR)/virtual reality (VR) can be utilized in a wide range of applications such as archeology, geography, and space tours where real-world access is not available, and to train employees where actual live training is greatly unsafe, for example, on-board offshore oil rigs, medical surgery training and diagnosis, and neuroscience [1]. In Industry 4.0, cyber-physical systems (CPS) monitor physical processes, create a virtual replica of the physical world (Digital-Twin concept), and make autonomous decisions [2]. CPSs interact and collaborate in real-time with one another and humans across the value chain throughout the Internet of Things [2]. [PERSON] et al. [3] introduced the concept of Operator 4.0 in the context of human cyber-physical systems (H-CPS) as systems designed to improve human abilities, human physical sensing, and cognitive capabilities through different technologies, since Industry 4.0 without human beings would be unthinkable. [PERSON] et al. [4] elucidated that visual computing is a crucial technology to smooth human-machine interactions on various levels of smart production, where AR/VR are the main parts of visual computing technologies to empower the operator in Industry 4.0 [2]. The integration of the human operator in Industry 4.0 nevertheless poses challenges in research, technology, and politics [3]. For example, [PERSON] et al. [5] explained that, to train operators and support them to perform tasks, the improvement of AR/VR experiences is crucial, where difficult interactions, misalignment of real/virtual models and better integration in real-world operator workspaces are the challenges of AR/VR. It is believed that, for any 3D-application, a VR framework should create a sensible dimension of authenticity that users can have confidence and be prepared to partake in [6]. VR innovations are, as yet, failing to give the realism that the real world can, because VR authenticity still experiences particular limitations [7], for instance, creating proper space visualizations of the environment and how selection and manipulation of objects in VR works are, thus far, the challenging problems [8]. [PERSON] et al. [9] argued that precise space visualization is critical in VR, which can enhance interaction performance and provide a virtual scene with satisfactory perceptual fidelity. [PERSON] et al. [10] also confirmed that the use of VR in industrial applications has been hindered because of visual discomfort and incorrect geometry perception. Accordingly, it is becoming increasingly difficult to overlook the investigation of visual space accuracy in VR. To explore the accuracy of visual space, two frames of reference are usually employed. According to a definition provided by [PERSON] and [PERSON] [11], the egocentric frame of reference utilizes the subject as a focal point of reference, while an exocentric frame of reference indicates the relative separation among objects and their corresponding orientations. So far, a considerable amount of studies in the VR literature has reported accuracy considering egocentric environments, in either extrapersonal or peripersonal space. For example, egocentric distance estimations are relatively accurate [12], underestimated [13; 14; 15; 16], and sometimes overestimated [6; 17; 16]. Thus far, in the exocentric space, comparatively limited numbers of studies have been reported, although researchers argued that numerous applications in a virtual environment indeed require the knowledge of exocentric distance. For example, [PERSON] and [PERSON] [6] pointed out and argued that performances in manipulation, navigation, and avatar control tasks are significantly influenced by exocentric distance judgments in peripersonal space. Similarly, [PERSON] and [PERSON] [18] urged that exocentric distance information is very important for numerous applications in virtual conditions.