Corneal Sphere Tracking for HMD Eye Models
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Solution Overview
Problem
Conventional eye tracking systems for head-mounted displays, particularly in virtual reality applications, lack the necessary accuracy due to limitations in the optical path quality, which affects the precision of gaze determination and user interaction.
Innovation Solution
An eye tracking system that utilizes at least two illumination sources and an optical sensor to model each eye by determining the radius and origin of a corneal sphere, allowing for accurate determination of the user's gaze direction, vergence angle, and accommodation depth, with a calibration process that includes identifying the pupillary axis and angular offset between the pupillary axis and the true line of sight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional tracking systems are used, then the system structure is simple, but the measurement precision of eye tracking is insufficient
Solution Approach 1:
The eye is segmented into multiple spherical components (cornea sphere, crystalline lens sphere, retina sphere) with distinct optical properties. This segmentation allows each component to be modeled and tracked independently, improving measurement precision while maintaining manageable system complexity through modular analysis
Solution Approach 2:
Corneal reflections serve as intermediary markers that mediate between the illumination sources and the optical sensor. These reflections provide precise geometric references for determining gaze direction and eye orientation, significantly enhancing tracking accuracy without requiring direct observation of internal eye structures
Solution Approach 3:
The system transitions from 2D image plane coordinates to 3D eye model coordinates by incorporating depth information through the spherical eye model and corneal reflection geometry. This dimensional transformation enables accurate determination of gaze direction and vergence angle in three-dimensional space
2Measurement precision
If multiple illumination sources and optical sensors are added to improve tracking accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The optical sensor serves multiple functions: capturing corneal reflections from multiple illumination sources, detecting pupil position, and tracking iris features. This multi-functionality allows a single sensor to gather comprehensive eye tracking data, improving measurement precision without proportionally increasing device complexity
Solution Approach 2:
The system performs preliminary calibration to determine user-specific parameters (sphere radii, centers, refractive indices) before actual eye tracking. This preliminary action creates a personalized eye model that enhances subsequent tracking accuracy while reducing the need for complex real-time computations during normal operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves enhanced accuracy in eye tracking, enabling precise gaze direction determination and user interaction, with a one-time single point calibration that stores user-specific data for future use, improving overall VR experience.
Implementation Method 1
the optical sensor can capture images of the illumination sources using reflections from the cornea of the eye
Data Source
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AI summary
A head mounted display (HMD) comprises an eye tracking system configured to enable eye tracking using light. The eye tracking system comprises two or more illumination sources positioned relative to one another and an optical detector for each eye. The optical detector is configured to capture images of the illumination sources using reflections from the eye. The system gathers data as the user views various objects in the HMD. The system determines a shape of the eye by determining one or more of a pupil shape, a foveal offset, and a corneal radius in three-dimensional space. The shape of the eye is used determine a three-dimensional position of the user's eye as well as a gaze direction.