Do Users Behave Similarly in VR? Investigation of the Influence on the System Design

Abstract

With the overarching goal of developing user-centric Virtual Reality (VR) systems, a new wave of studies focused on understanding how users interact in VR environments has recently emerged. Despite the intense efforts, however, current literature still does not provide the right framework to fully interpret and predict users trajectories while navigating in VR scenes. This work advances the state-of-the-art on both the study of users’ behaviour in VR and the user-centric system design. In more details, we complement current datasets by presenting the first publicly available dataset that provides navigation trajectories acquired for heterogeneous omnidirectional videos and different viewing platforms, namely, head-mounted display, tablet and laptop. We then present an exhaustive analysis on the collected data, to better understand navigation in VR across users, content, and for the first time across viewing platforms. The novelty lies in the user-affinity metric, proposed in this work to investigate users’ similarities when navigating within the content. The analysis reveals useful insights on the effect of device and content on the navigation, which could be precious considerations from the system design perspective. As a case study of the importance of studying users’ behaviour when designing VR systems, we finally propose an user-centric server optimisation. We formulate an integer linear program that seeks the best-stored set of omnidirectional content that minimises encoding and storage cost while maximises the user’s experience. This is posed while taking into account network dynamics, type of video content, but also user population interactivity. Experimental results prove that our solution outperforms commonly company recommendations in terms of experienced quality but also in terms of total cost, achieving a saving up to 70%. More importantly, we highlight a strong correlation between the storage cost and the user-affinity metric, showing the impact of the latter in the system architecture design.

Users dataset across VR devices

Our work contributes to the overall open problem of optimally designing a VR system, with the following main contributions:

  1. A new public dataset of 15 ODVs with associate navigation trajectories collected in a task- free experiments using three different devices such as HMD, tablet, and laptop.
  2. An exhaustive analysis of the aforementioned collected data, showing that users navigate differently based on the device, and introducing a novel affinity metric able to quantify user navigation similarities.
  3. A case study of VR systems optimised from the server perspective, with a two-fold novelty: (i) the proposed problem formulation; (ii) the translation of the users’ behaviour analysis into gain for a system provider.


Authors

Silvia Rossi |Cagri Ozcinar | Aljosa Smolic | Laura Toni

Dataset and code

The open source codes and dataset presented in this paper are avilable in the repository here.

Citation

Please cite our paper in your publications if it helps your research:

@article{rossi2020, 
title = {Do users behave similarly in VR? Investigation of the influence on the system design}, 
author = {Silvia Rossi and Cagri Ozcinar and Aljosa Smolic and Laura Toni}, 
year = {2020}, 
booktitle = {Transactions on Multimedia Computing Communications and Applications} }

Acknowledgement

This work has been partially funded by Adobe under Academic Donation scheme. Also, this publication has emanated from research supported in part by a research grant from Science Foundation Ireland (SFI) under the Grant Number 15/RP/2776.