# Mixed Reality: A Reconsideration Based on Mixed Objects and Geospatial Modalities
## 1 Introduction  
Mixed Reality (MR) is closely associated, if not synonymous, with digital applications in which visual representations are based on the overlaying of virtual objects on the real world [1]. As such, MR is considered a highly demanding experience in terms of the size of the content involved, the processing capacity of the equipment involved as well as telecommunication media and relevant infrastructure capabilities required. For example, the digital representation of an area along with virtual reconstructions and sophisticated visualizations involves heavy-sized multimedia content. For this content to be transmitted from the content provider to the content consumer and be executed, there is a need for high-speed networks and devices with high-process capabilities. However, several technological advancements have emerged and are being applied, promising to satisfy the above demands. Focusing on these, first and foremost one should definitely mention the boosting of wireless data transmission with the fifth-generation technology standard, 5G, which introduces data transmission capabilities with speeds up to 1 Gbps [2]. Practically this means that a rich Digital Surface/Terrain Model (DSM/DTM) will potentially be downloaded on a mobile device in a few seconds. Secondly, but equally ranked, is the ever-increasing processing capacity, combined with the continuous cost reduction of affordable mobile smart devices [3]. Last but not least, the penetration of cloud services into organizations [4] is a quite convenient setting, releasing them from the obligation ofdeveloping and maintaining demanding hardware and software infrastructure for their services to be provided. Finally, one can imagine how easy it has become today for an authority or a content provider to share high-resolution digital content without the need for telecommunication infrastructure on-site and/or special equipment for visitors, just a mobile phone with normal capabilities. All this technological progress unlocks potential synergies of MR and other disciplines involved in digital content development, such as geoinformatics, which, among others, provides a set of tools and technologies for digitizing real-world objects including surfaces, borderlines, and areas, as well as spatial entities of the natural and anthropogenic environment such as trees, buildings, etc. Although these two disciplines have no previous and clearly defined established synergies as such, we can mention some critical paradigms that prove how strongly they are connected. Firstly, the DSM/DTM, as well as the digital aspect of the spatial entities of the physical environment in an MR experience, can be developed via topographic surveying and mapping methods such as LiDAR and Photogrammetry. In addition, the spatial reference of a Virtual/Augmented Reality (VR/AR) world may be achieved by Georeference procedures [5], while many other functionalities related to Geographical Information Systems (GIS), are applicable in the digital content, such as the association of spatial features with descriptive attributes. Furthermore, by employing Javascript geospatial libraries it is possible to develop virtual Geospatial Worlds. A Geospatial World practically includes the development of a 3D terrain upon which sophisticated visualizations and animation and motion effects on spatial objects take place [6]. As said above, a heavy-sized digital content can be easily transmitted by a provider and received on a smart device; therefore, a Geospatial World containing DTM/DSM and other georeferenced 3D models can exist on an end-user device and can be overlaid with the real world captured by the camera. In the present study, we make an attempt to reconsider the concept of MR focusing on the interaction between virtual and real objects, stressing that this is the key issue that differentiates MR from VR and AR.