Railway Vehicle Sensor Calibration Using Trackside Markers
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Solution Overview
Problem
Existing methods for calibrating environmental sensors on rail vehicles, such as video cameras, are cumbersome and inaccurate due to the need for precise manual measurements and the complexity of designing multiple calibration patterns for varying focal lengths and installation positions, especially when sensors are mounted above the vehicle body.
Innovation Solution
A method involving a calibration marker placed on the track with a defined lateral position relative to the track center, allowing sensors to record image data sets while traveling, which are then optimized to determine the sensor's coordinate transformation using a mathematical minimization problem, eliminating the need for manual measurements and complex pattern design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual measurement is used to determine coordinate transformation, then the calibration can be performed, but the accuracy is insufficient and the process is cumbersome
Solution Approach 1:
The patent replaces manual mechanical measurement with an automated image-based calibration system. The environment sensor captures images of a calibration marker, and computational algorithms automatically determine the coordinate transformation, eliminating the need for manual measurement while achieving high accuracy.
Solution Approach 2:
The calibration system performs self-calibration by automatically processing images of the calibration marker to determine the coordinate transformation. The system uses the captured images and known marker geometry to compute calibration parameters without requiring external manual intervention or complex measurement procedures.
2Measurement precision
If multiple calibration patterns are designed for different focal lengths and installation positions, then the calibration can be optimized for each sensor configuration, but the device complexity and development effort increase significantly
Solution Approach 1:
The patent employs a single universal calibration marker that can be used for calibrating environmental sensors with various focal lengths and installation positions. The marker's design and positioning allow it to serve multiple calibration purposes across different sensor configurations, eliminating the need to develop separate calibration patterns for each scenario.
Solution Approach 2:
The patent achieves adaptability to different sensor configurations by changing the position and orientation of the calibration marker relative to the sensor during calibration. By adjusting the marker's location and the sensor's viewing geometry, the same marker can provide accurate calibration data for various focal lengths and mounting positions without requiring physical modifications to the marker itself.
3Ease of operation
If the calibration marker is positioned high to accommodate sensors mounted above the vehicle body, then the sensor can capture the marker, but the calibration becomes more complex and less accurate
Solution Approach 1:
The patent addresses the challenge of high-mounted sensors by utilizing three-dimensional spatial positioning of the calibration marker. The marker is positioned at known locations in 3D space, and the system uses the sensor's capture of the marker from elevated positions to compute accurate calibration parameters, effectively transitioning from a two-dimensional ground-level calibration to a three-dimensional calibration approach that accommodates various sensor mounting heights.
Data Source
Figure 1~2
AI summary
The invention relates to a method for calibrating an environmental sensor (8), in particular a video camera, arranged on a rail vehicle (1). The environmental sensor (8) is designed to acquire image data sets (c), each representing a section of the environment within its field of view. In the area of a track with a straight track section (2), a calibration marker (6) is arranged in a defined lateral position relative to the center point (5) of the track section (2). During a calibration run of the rail vehicle (1) on the track section (2), the environmental sensor (8) acquires a sequence of image data sets (c) containing the calibration marker (6). From the acquired image data sets (c), a sequence of positions of the environmental sensor (8) relative to the calibration marker (6) is determined.The relative position of the environmental sensor (8) to the track center (5) is determined by solving an optimization problem subject to the constraint that the determined sequence of positions of the environmental sensor (8) relative to the calibration mark (6) lies on a straight line (g). This provides a flexible extrinsic calibration method with which several environmental sensors (8) arranged on a rail vehicle (1) can also be calibrated in different configurations.