Virtual Point Calculation for Ophthalmic Lens Measurement
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Solution Overview
Problem
Existing methods for measuring the center of rotation of the eye for corrective lens customization are prone to errors due to precise alignment requirements with the camera's optical axis, leading to inaccurate data and suboptimal glasses manufacturing.
Innovation Solution
A method using a virtual remarkable point (PRV) is introduced, where the subject's gaze is directed at a fixing point, and images are taken from different angles, allowing for geometric modeling and calculation of the PRV's position, even when the gaze axis is not aligned with the camera's optical center, using a mirror to simulate distant vision and reduce measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the subject's gaze is aligned with the camera's optical center, then the measurement of the center of rotation is accurate, but the operation becomes complex and time-consuming due to precise alignment requirements
Solution Approach 1:
The patent introduces a mirror as an intermediary device between the subject and the camera. The mirror reflects the camera's optical center to create a virtual image, which the subject gazes at instead of directly at the camera. This intermediary allows the subject's gaze to be naturally aligned with the optical axis without requiring complex manual alignment procedures, thus resolving the contradiction between measurement accuracy and ease of operation
Solution Approach 2:
The patent creates a virtual copy of the camera's optical center through the mirror reflection. The virtual image of the optical center serves as a gaze target that is optically equivalent to the actual optical center, allowing measurements to be taken without direct alignment while maintaining measurement accuracy. This copying approach simplifies the operational complexity
2Measurement precision
If multiple images are captured from different angles to calculate parallax, then the measurement precision improves, but the measurement time increases
Solution Approach 1:
The patent performs preliminary actions by having the subject wear a headrest with fixed reference markers before image capture. The headrest pre-establishes a known geometric relationship and spatial reference system, allowing the software to automatically calculate the center of rotation from standard images without requiring complex real-time adjustments or multiple angled captures, thus reducing measurement time while maintaining precision
Solution Approach 2:
The patent changes the measurement approach from capturing multiple images at different angles to capturing standard images and using software-based parallax calculation with pre-defined geometric models. This parameter change in the measurement methodology reduces the number of physical image captures needed while maintaining measurement accuracy through computational methods
3Ease of operation
If the subject does not precisely fixate the camera's optical center, then the ease of operation improves, but the measurement precision deteriorates due to gaze misalignment errors
Solution Approach 1:
The mirror serves as an intermediary that creates a virtual image of the optical center at a distance that is comfortable for the subject's gaze. This allows the subject to naturally fixate on the virtual image without strain while ensuring that the line of sight passes through the actual optical center, thus maintaining measurement precision while improving ease of operation
Solution Approach 2:
The patent introduces a temporal dimension by capturing a sequence of images and using software to analyze gaze direction over time. This allows the system to calculate the center of rotation even if individual frames show slight misalignment, as the software can process multiple frames to compensate for minor gaze variations, thus maintaining precision while allowing easier 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
This approach provides more accurate measurements of the eye's center of rotation and Frankfurt Plan, reducing errors in corrective lens customization and simplifying the measurement process, making it more user-friendly and efficient.
Implementation Method 1
using a mirror to simulate distant vision and reduce measurement errors
Data Source
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AI summary
The invention relates to a method for measuring the position of a virtual characteristic point (PRV) associated with the face of a person wearing corrective lenses, said method comprising: a step consisting in acquiring at least two images of the wearer's face using an image acquisition means; a step consisting in estimating the position of the face in relation to the image acquisition means; and a step consisting in determining, on the images, the co-ordinates (Xpref, Ypref) of reference points associated with the face. Moreover, given that the virtual characteristic point is visible on at most one image and that the position of the virtual characteristic point is connected to the co-ordinates of the reference point(s) by a predetermined geometric relationship, the measurement method also comprises a step consisting in calculating at least one of the co-ordinates (XPRV, YPRV, ZPRV) of the virtual characteristic point (PRV) on the basis of the reference point(s), using the geometric relationship.