# 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. - **Patent:** US 10444502 - **Original title:** Method and apparatus for multiple user self-relative tracking for augmented reality systems using magnetic tracking - **Owner:** Sixense Enterprises - **Granted:** 2019 - **Status:** Active - **Times cited:** 0 - **Field:** consumer_electronics, software, telecommunications, gaming, ai_ml ## What it does 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 does NOT 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. ## 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 ## 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. ## Frequently asked questions ### What does How Two People's Body Movements Are Tracked in Augmented Reality cover? 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. ### Who owns patent US 10444502? Sixense Enterprises owns this patent, granted in 2019. ### When does this patent expire? This patent is expected to expire on July 31, 2039, when the invention enters the public domain. ### What problem does this patent solve? 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. ### What does this patent NOT cover? Tracking systems that rely solely on a fixed base station to determine the position of body parts, rather than relative to the HMD. **Full plain-English explainer:** https://patentbrief.org/patent/us/10444502/method-and-apparatus-for-multiple-user-self-relative-tracking-for-augmented-real **Original patent:** https://patents.google.com/patent/US10444502 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Disney's Compact AR Display Uses Special Mirrors](https://patentbrief.org/patent/us/12386177/compact-augmented-reality-virtual-reality-display) — Disney's patent describes a compact augmented reality display that uses a clever arrangement of three special wavelength-splitting mirrors to efficiently show digital images layered over the real world. - [How Devices Detect Touch Using Heat Signatures](https://patentbrief.org/patent/us/20210117042/method-and-device-for-detecting-a-touch-between-a-first-object-and-a-second-obje) — This patent describes a system that uses a thermal camera to detect when two objects, like a finger and a screen, touch by looking for a specific temperature change at their contact point. - [How Eye Tracking Systems Adapt When They Can't See Eye Glints](https://patentbrief.org/patent/us/10878237/systems-and-methods-for-performing-eye-gaze-tracking) — This patent describes an eye-tracking system that intelligently switches between two methods: one using bright reflections on the eye when available, and another using head position and facial features when those reflections are absent. - [How Snap's AR Tech Measures Distance for Virtual Button Presses](https://patentbrief.org/patent/us/12008152/vision-pro-persona) — A method for mobile devices to calculate exactly when a user's finger or controller touches a virtual object in augmented reality by measuring precise distances from the camera. - [How AR Glasses Make Virtual Objects Look Solid](https://patentbrief.org/patent/us/10573086/opacity-filter-for-display-device) — This patent describes how augmented reality glasses can make virtual objects appear more distinct by selectively blocking real-world light behind them using a special pixelated filter.