How Two People's Body Movements Are Tracked in Augmented Reality

This patent describes a system for two users to accurately track their body parts, like a limb, relative to their own head-mounted display using magnetic fields, then display these virtual limbs in a shared augmented reality.

What it covers

This system allows two users wearing head-mounted displays (HMDs) to see their own and each other's virtual limbs in an augmented reality (AR) environment. Each HMD has its own tracking system to know its absolute position in the real world (Claim 1). For each user, a magnetic tracking system is used, with one magnetic coil attached to their HMD and another to a limb, like an arm or leg (Claim 1). A processor then figures out the limb's position relative to the HMD using the magnetic data. It combines this with the HMD's absolute position to know the limb's exact location in the real world. Finally, the system displays a virtual version of each user's limb on both HMDs, making it appear in the correct place within the shared AR experience (Claim 1). For example, two friends could be playing an AR game together, and each would see their own and the other's virtual arms moving correctly as they interact with virtual objects.

What it doesn't cover

• —Tracking systems that rely solely on a fixed base station to determine the position of body parts, rather than relative to the HMD.
• —Systems that use optical cameras, inertial sensors, or other non-magnetic methods for tracking body parts.
• —Single-user augmented reality experiences; this patent specifically claims a system for "two head-mounted displays" and "multiple user self-relative tracking."
• —Virtual reality (VR) systems that replace the entire real world with a virtual one, as it focuses on displaying "augmented reality."
• —Tracking of entire body skeletons or facial expressions, as the claims specifically refer to tracking a "limb."

The clever bit

The core innovation is tracking a user's body parts, like a limb, relative to their own head-mounted display using magnetic fields, rather than relative to a fixed point in the room. This "self-relative" approach minimizes magnetic field distortions, allowing for a much more accurate representation of the user's virtual body in augmented reality.

Why it matters

Accurate body tracking is crucial for creating believable and immersive augmented reality experiences, especially for interactions between multiple users. By tracking limbs relative to the HMD, this system aims to reduce errors caused by magnetic field distortions, which are common when tracking from a distant base station. This improved accuracy helps make virtual avatars feel more connected to the user's actual movements, enhancing shared AR applications in gaming, training, and collaborative work.

Real-world examples

• 1.High-end augmented reality headsets with full-body tracking accessories
• 2.Collaborative AR applications for design or training
• 3.VR/AR gaming systems that track hands or feet for interaction
• 4.Professional simulation environments using magnetic trackers