Camera Movement Correction Using Reference Markers
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Solution Overview
Problem
Existing systems for determining whether a ball has crossed a goal line in ball sports are unreliable due to issues with sensor placement on the ball or goal posts, which can alter the ball's weight and balance, and struggle to differentiate between the ball and other objects, and are prone to movement and misalignment.
Innovation Solution
A camera-based system that uses reference markers to correct for camera movement and determine the position of a ball within a scene, employing multiple cameras positioned around the goal line to capture images and apply corrective transforms to ensure accurate detection of the ball's position and trajectory, even when obscured.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor is fitted inside the ball to detect position, then the ball position can be tracked accurately, but the ball's weight and balance are altered
Solution Approach 1:
The detection system is segmented into multiple independent camera units positioned around the goal line, each capturing images from different angles. This eliminates the need for a single sensor inside the ball, thereby avoiding weight and balance alterations while maintaining tracking accuracy through multi-perspective observation.
Solution Approach 2:
A reference marker is introduced as an intermediary element attached to the ball, which is detected by external cameras rather than using internal sensors. This intermediary approach allows position tracking without inserting weight-altering components into the ball itself.
2Device complexity
If sensors are placed on goal posts to detect ball crossing, then goal line detection is simplified, but the system cannot differentiate between the ball and other objects
Solution Approach 1:
The detection function is segmented across multiple camera units positioned at different locations and angles around the goal line. Each camera captures images of the entire scene including the ball, reference marker, and surrounding objects. This multi-perspective segmentation enables reliable ball identification through spatial and temporal analysis rather than simple presence detection.
Solution Approach 2:
The reference marker attached to the ball has distinct visual characteristics (color, pattern, or reflectivity) that differentiate it from other objects in the scene. The camera system detects these unique visual features to reliably identify the ball's position and crossing events, avoiding confusion with players or other objects.
3Ease of manufacture
If goal posts are used as sensor mounting points, then installation is simplified, but the goal posts experience movement and misalignment during matches
Solution Approach 1:
The system incorporates dynamic correction by continuously monitoring the positions of reference markers (including those on goal posts) and calculating corrective transforms. This allows the system to adapt to movements and misalignments in real-time, maintaining measurement precision despite physical changes in the goal post positions during matches.
Solution Approach 2:
The system uses feedback from detected reference marker positions to continuously correct for camera movement and goal post displacement. By comparing expected versus actual reference marker positions, the system generates corrective transforms that maintain accurate ball position detection despite environmental changes.
Data Source
AI summary
A camera movement correction apparatus for use in a system which detects the position of a sporting projectile within a scene, the apparatus comprising: an interface operable to receive a first and second image of the scene captured by a camera; a reference marker determiner operable to determine the position of a reference marker within the first and second image of the scene, the reference marker being static within the scene; a difference determination device operable to determine the difference between the position of the reference marker in the first and second image of the scene; and a corrective transformer operable to apply a corrective transform to the second image on the basis of said determined difference.