Vehicle Camera Extrinsic Calibration Using a Ground Reference Plate
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Solution Overview
Problem
Current methods for calibrating external parameters of image acquisition devices in automatic driving vehicles lack accuracy and require specialized setups or have limited adaptability, especially when calibrating cameras with downward fields of view.
Innovation Solution
A method and apparatus that utilize a calibration plate on the ground within the camera's field of view, determining conversion matrices from image pixel coordinates to calibration plate coordinates and from calibration plate coordinates to vehicle body coordinates, allowing for precise calibration of external parameters without the need for specialized sites or high-precision sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a prearranged checkerboard calibration board is used to calibrate external parameters, then calibration can be performed in small field of view and close-range scenes, but the calibration board must be within the field of view and cannot be blocked, and it is difficult to convert external parameters to body coordinate system
Solution Approach 1:
The patent introduces a calibration board with specific coordinate markings as an intermediary object that can be placed on the ground. This calibration board serves as a mediator between the camera and the vehicle body coordinate system, enabling parameter conversion through the establishment of a calibration board coordinate system that links image coordinates to real-world coordinates.
Solution Approach 2:
The patent transitions from traditional 2D checkerboard calibration to a 3D spatial calibration approach by placing the calibration board on the ground plane and using its known geometric dimensions to establish coordinate transformations across multiple dimensions, enabling conversion to the vehicle body coordinate system.
2Measurement precision
If a special calibration site is established for high precision calibration, then calibration accuracy is improved, but special site support is required
Solution Approach 1:
The calibration board is designed to be self-contained with printed coordinate markings and known geometric dimensions. It can be independently placed on any flat ground surface without requiring specialized calibration infrastructure, making the calibration system self-sufficient and portable.
Solution Approach 2:
The calibration board is implemented as a simple, inexpensive printed plate that can be easily manufactured and replaced. It uses standard printing techniques rather than precision mechanical structures, reducing cost and complexity while maintaining calibration accuracy.
3Adaptability or versatility
If dynamic calibration method combined with motion estimation is used, then calibration can be performed without special site, but calibration accuracy is low and relies on other sensors
Solution Approach 1:
The patent replaces dynamic motion estimation methods with a static geometric calibration approach. Instead of relying on sensor fusion and motion tracking, it uses the known geometric dimensions of the calibration board and perspective projection geometry to directly calculate external parameters, eliminating dependence on additional sensors.
Solution Approach 2:
The patent changes the calibration parameters from dynamic sensor measurements to static geometric relationships. By using the fixed, known dimensions of the calibration board and the camera's projection model, it transforms the calibration problem into a geometric parameter estimation task that can be solved through image processing and mathematical computation.
4Ease of operation
If conventional calibration methods are used for downward field of view cameras, then calibration can be performed, but shielding issues occur and multiple cameras cannot be calibrated simultaneously
Solution Approach 1:
The calibration process is designed to be performed once for the entire vehicle system. The calibration board remains stationary on the ground while multiple cameras capture images simultaneously or sequentially, eliminating the need to move the calibration board between cameras and ensuring consistent reference frame for all cameras.
Data Source
AI summary
The present application discloses a method and an apparatus for calibrating external parameters of an image acquisition device, a device and a storage medium, and relates to the technical field of vehicle positioning. The specific implementation solution is as follows: acquiring an image captured by the image acquisition device; determining a plurality of marking points on a calibration plate in the image; determining a first conversion matrix based on coordinates of each of the marking points in the image pixel coordinate system and the calibration plate coordinate system; determining a second conversion matrix based on coordinates of at least one wheel grounding point of the vehicle in the calibration plate coordinate system and the vehicle body coordinate system; and determining external parameters of the image acquisition device by using the first conversion matrix and the second conversion matrix.