# Off-Cloud Anchor Sharing Framework for Multi-User and Multi-Platform Mixed Reality Applications
## 6 Key Findings  
The results presented in Section 5 highlight the growing complexity of anchor sharing in large environments, where the significant increase in anchor size directly impacts transmission and loading times. In particular, the serialization, segmentation and transfer of large anchors require more processing and communication overhead, resulting in higher latency during initial synchronization. However, this does not present a long-term issue, as the system proposed in this article was specifically designed with these challenges in mind. Anchors are stored locally on each device after the initial synchronization, meaning that anchor sharing only needs to be performed once per location and user. This approach significantly reduces communications overhead and ensures that spatial alignment remains consistent across sessions, making the system a robust and scalable solution for multi-user, multi-platform MR applications. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**\# Exp** & **Anchor Size (MB)** & **Transmission Time (s)** & **Client Loading Time (s)** \\ \hline
1—Small Anchors & 3.00 & 12.969 (\(\pm\)0.55) & 0.890 (\(\pm\)0.22) \\ \hline
2—Medium Anchors & 6.00 & 25.682 (\(\pm\)0.03) & 1.472 (\(\pm\)0.18) \\ \hline
3—Big Anchors & 10.10 & 43.477 (\(\pm\)0.09) & 2.639 (\(\pm\)0.38) \\ \hline
4—Room-Size Anchors & 20.10 & 85.845 (\(\pm\)0.38) & 5.265 (\(\pm\)0.58) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Second experiment (remote): average values and standard deviation for anchor size and operation times for each experiment scenario. The proposed system was designed with cross-platform compatibility in mind, with the current implementation focusing specifically on Microsoft HoloLens 2 and desktop environments. As such, mobile platforms (i.e., iOS, Android) were not included in the experimental evaluation, as no specific development was conducted for these devices in the present version of the framework. The implementation of the proposed system was centered on the MRTK for HoloLens 2, as this platform remains relatively less explored in comparison to mobile AR devices or mainstream VR frameworks. Supporting cross-platform MR requires non-trivial development efforts due to platform-specific differences, APIs and, especially, spatial mapping capabilities. For example, anchor sharing in ARKit (iOS) and ARCore (Android) mobile devices differ significantly from those used with the MRTK, requiring a new implementation or adaptation of key components such as anchor compatibility. Although the use of Unity ARFoundation provides a common layer that supports various plugins (i.e., OpenXR for HoloLens, ARKit for iOS and ARCore for Android devices), according to Unity official documentation [39], core features such as anchors are supported across such platforms, which suggests the proposed framework could be adapted to modern MR headset devices. Cross-platform transmission and synchronization of the exported serialized anchor data would remain using the same modules of the proposed framework. However, the compatibility of the anchor data structure among these platforms (e.g., whether an anchor exported from HoloLens 2 can be imported directly on Apple Vision Pro) remains uncertain and would require further investigation, as no specific documentation regarding such suitability was found at the time of writing this paper. In such cases, platform-specific anchor conversion mechanisms or alternative synchronization methods may be needed. Thus, cross-platform compatibility could be feasibly integrated into the proposed framework through the use of fiducial markers (e.g., ArUco codes or QR-based visual markers). These markers could serve as a common reference system, enabling spatial alignment and synchronization across heterogeneous devices. This approach would allow mobile devices and other modern MR headsets such as Apple Vision Pro to participate in the shared experience in a more immersive way.