Stacked Retargeting: Combining Redirected Walking and Hand Redirection to Expand Haptic Retargeting's Coverage

Title of the Paper

Stacked Retargeting: Combining Redirected Walking and Hand Redirection to Expand Haptic Retargeting’s Coverage

Paper Information

• Subject Area: Virtual Reality (VR) and Haptics
• Keywords: Virtual Reality, Haptic Retargeting, Hand Redirection, Redirected Walking, Interaction Coverage, Passive Haptic Proxy, Spatial Interaction

Research Background and Problem

• Research Problem:

  • Problem Context: Current haptic retargeting is primarily limited to static hand redirection, allowing a single physical proxy (e.g., a cup) to be mapped to multiple virtual objects only within a limited physical space.
  • Limitations:
    • Haptic retargeting requires proxies to be mapped to virtual objects that are very close in proximity, necessitating a large number of physical proxies to cover the entire interaction space.
    • Using hand redirection or walking redirection alone has limitations in matching multiple virtual objects to a single physical proxy.
  • Challenges in Existing Technologies:
    • The range within which significant spatial misalignment is imperceptible to users is limited; exceeding this threshold leads to a notable decline in user experience.
    • Spatial and directional constraints restrict the usability of haptic devices.

• Research Motivation:

  • To more efficiently utilize a limited number of physical objects and expand their coverage as haptic proxies in virtual environments.
  • To overcome the limitations of single redirection techniques by combining redirected walking and hand redirection.

Solution

• Proposed Solution:

  • Introduce "Stacked Retargeting," which combines hand redirection and redirected walking to increase the coverage of a single physical proxy as haptic feedback for multiple virtual objects.
  • Provide a phased implementation approach:
    1. Determine whether hand redirection alone can achieve the mapping.
    2. Identify the optimal interaction position the user needs to reach for haptic coverage.
    3. Guide the user to the target position via walking paths.
    4. Adjust the offset between the user's physical and virtual positions.

• Technologies and Methods:

  1. Implement five redirected walking path strategies to extend the alignment range between virtual objects and physical proxies:
     • Turn and Arc: Initial turning followed by an arced walking path.
     • Walk-while-turn: Simultaneous turning during walking.
     • L-Shaped Path: Segmental alignment through an L-shaped path.
     • Turn-walk-turn: Turning at both the starting and ending points.
     • Zigzag: A zigzag path to adjust the user's trajectory over a larger range.
  2. Provide algorithms and pseudocode for quickly calculating alignment between virtual objects and physical proxies.
  3. Combine redirected walking and hand redirection to expand the user's interaction range.

Research Outcomes

• Specific Outcomes:

  • Validated that the stacked retargeting method significantly expands the haptic coverage of proxy objects.
  • Proposed and evaluated five redirected walking strategies, each with varying impacts on walking time, perceived naturalness, and user experience.
  • Experimental results indicate that segmented paths (e.g., L-Shaped Path and Zigzag) have less impact on user experience compared to continuous paths (e.g., Walk-while-turn).

• Advantages Over Existing Solutions:

  • Stacked retargeting overcomes the limitation of single hand redirection being confined to static scenarios, enabling physical proxies to serve as haptic feedback for multiple virtual objects across a broader space.
  • The combination of redirected walking and hand redirection addresses the shortcomings of each technique when used independently.

• Experiments and Evaluation Results:

  • User Subjective Experience:
    • Among all solutions, compound path strategies based on head turning provided the best user experience.
    • Continuous synchronous redirection (Walk-while-turn) had the lowest user acceptance, with more pronounced issues of perceived misalignment.
  • Walking Dynamics:
    • Compound paths like Zigzag and Turn-walk-turn required longer paths and more time but were perceived as more natural by users.
    • Direct paths, while shorter, resulted in greater perceived misalignment and lower user satisfaction compared to compound paths.

• Limitations and Future Directions:

  • Limitations:
    • Requires a relatively large physical space to support complex paths.
    • Needs more flexible adaptation algorithms to handle user deviations from predefined paths.
    • Further optimization is required to support more complex interaction surface shapes.
  • Potential Future Directions:
    • Explore dynamic path updates and early integration of hand redirection.
    • Extend the technology to more complex interaction scenarios, such as non-tabletop surfaces, walls, and corridors.
    • Combine with other redirection techniques, such as "change blindness jumps" or drone-based haptic devices, to further enhance VR haptic effects.