Camera Offset Calibration via Pan-Tilt Angle Correction
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Solution Overview
Problem
Pan-tilt camera systems face challenges in precision positioning, especially when using wide angle lenses not mounted on the camera head but rather fixedly attached to a support structure, leading to misalignments and reduced image sensor utilization.
Innovation Solution
A method for calibrating the camera system by centering the projected image view on the image sensor through tilting the camera head and adjusting its position based on calculated angles from the overview image coordinates, using trigonometric equations to approximate pan and tilt angles, and employing edge detection and Hough Transform for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the lens is fixedly attached to a support structure instead of being mounted on the camera head, then the device complexity is reduced, but the manufacturing precision and positioning precision deteriorate due to mounting misalignments
Solution Approach 1:
The patent performs calibration before actual operation by capturing an overview image and calculating correction values for pan and tilt angles. This preliminary calibration establishes a transfer function that compensates for the misalignment between the lens optical axis and camera head optical axis, ensuring precise positioning despite the simplified fixed attachment structure.
Solution Approach 2:
The patent changes the parameters of the transfer function from ideal geometric relationships to empirically determined values. By capturing images at multiple known pan-tilt positions and calculating actual versus expected image coordinates, the system derives corrected transformation parameters that account for the physical misalignment, thereby maintaining positioning precision without complex mechanical mounting.
2Ease of manufacture
If the lens is fixedly attached to a support structure, then the ease of manufacture is improved, but the positioning precision worsens due to misalignments in the field
Solution Approach 1:
The calibration process is performed in advance during installation or setup. The system captures an overview image at a known position, calculates the actual image coordinates, and determines correction values that will be applied during operation. This preliminary action eliminates the need for precise mechanical alignment during manufacturing while ensuring measurement precision during use.
Solution Approach 2:
The system uses feedback from the captured overview image to determine the actual positioning of the camera head relative to the lens optical axis. By comparing expected versus actual image coordinates, the system generates correction values that are fed back into the transfer function, continuously compensating for manufacturing tolerances and ensuring precise positioning.
3Device complexity
If standard geometric transformation is used to calculate pan and tilt angles from image coordinates, then the device complexity is reduced, but the positioning precision deteriorates due to misalignment errors
Solution Approach 1:
Instead of directly using standard geometric transformation during operation, the system performs a preliminary calibration by capturing images at multiple known pan-tilt positions. This preliminary action establishes an empirical transfer function that accounts for misalignments, which is then used during actual operation to achieve higher precision without increasing computational complexity.
Solution Approach 2:
The patent transforms the parameters from ideal geometric relationships to empirically determined transformation values. By capturing overview images at multiple positions and calculating the difference between expected and actual image coordinates, the system derives corrected pan and tilt angle parameters that compensate for misalignment errors while maintaining simple calculation methods.
Data Source
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AI summary
The present invention relates to a method for calibrating offset between a selected position in an overview image and a centre position in a detailed image. The overview image being captured by an overview camera and the detailed view being captured by a detailed view camera, these two cameras being different cameras. The method comprising: capturing overview image by overview camera; displaying captured overview image including an overlay pattern (1300) presenting indicators (1302a - 1302d) of at least three suggested selection areas; adjusting orientation of overlaid indicators of selection areas; selecting a point in a selection area at a feature in the overview image; transforming coordinates representing the point into a pan angle and a tilt angle; panning and tilting the detailed view camera in accordance with the pan angle and the tilt angle; capturing detailed image using the detailed view camera after the camera has been panned and tilted in accordance with the pan angle and the tilt angle; adjusting the pan angle and the tilt angle so that the feature at the selected point in the overview image is substantially in the centre of the image captured by the detailed view camera; storing information indicating the difference between the transformed pan and tilt angles and the adjusted pan and tilt angles as an offset value; repeating the steps of selecting a point, transforming coordinates, panning and tilting capturing detailed image, and storing offset value for the other selection areas.