Extrinsic Camera Calibration Using Co-Planar Markers
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Solution Overview
Problem
Existing methods for extrinsic calibration of non-globally overlapping camera systems are not robust to outliers and spurious detections of fiducial markers, require a priori knowledge of spatial relationships, and often lack support for multiple reference frames, making them cumbersome and less precise.
Innovation Solution
The method employs co-planar markers, such as those printed on sheets or projected onto surfaces like walls and floors, using the Levenberg-Marquardt algorithm to iteratively adjust camera poses and reference plane positions, ensuring markers are co-planar to a reference plane, thereby simplifying the calibration process and improving precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fiducial marker methods are used for extrinsic calibration, then camera pose can be determined, but the method is not robust to outliers and spurious detections
Solution Approach 1:
The patent introduces a reference plane as an intermediary element that mediates between multiple fiducial markers and the camera system. By requiring markers to be co-planar with the reference plane, the system creates a geometric constraint that serves as a mediator to verify and filter spurious detections. The reference plane acts as a common reference frame that all markers must satisfy, providing a robust mechanism to eliminate outliers while maintaining calibration precision.
2Ease of operation
If multiple fiducial markers with known spatial relationships are used, then calibration can be performed, but a priori knowledge of spatial relationships is required
Solution Approach 1:
The patent segments the calibration system into independent fiducial markers that are placed on a common reference plane. Instead of requiring a single complex marker with predefined spatial relationships, the system uses multiple independent markers whose only requirement is co-planarity. This segmentation allows each marker to be independently detectable and simplifies the overall setup, as users only need to ensure markers lie on the same plane rather than maintaining complex spatial relationships between them.
3Adaptability or versatility
If existing calibration methods are used, then camera poses can be estimated, but support for multiple reference frames is lacking
Solution Approach 1:
The reference plane serves as a universal reference frame that can accommodate multiple fiducial markers and support multiple camera coordinate systems simultaneously. The co-planarity constraint provides a common geometric foundation that works across different reference frames and camera configurations. This universal approach allows the system to handle multiple reference frames without requiring separate calibration procedures for each, enhancing adaptability while maintaining a relatively simple calibration structure.
4Measurement precision
If co-planar markers on a reference plane are used, then extrinsic calibration precision is improved, but the method requires establishing an accurate reference plane
Solution Approach 1:
The system uses the fiducial markers themselves to define and establish the reference plane through their co-planar arrangement. Instead of requiring external equipment or complex procedures to establish the reference plane, the markers' geometric configuration automatically serves to define it. The co-planarity of the markers self-creates the reference plane, eliminating the need for separate reference plane establishment procedures and enabling users to achieve high precision through simple marker placement on any flat surface.
Data Source
AI summary
Examples of the present disclosure relate to a computer-implemented method, an apparatus, and a computer program for extrinsic calibration of one or more cameras with respect to a reference coordinate system, and to various methods, apparatuses, and computer programs for using information on a pose of a reference plane being determined as part of the extrinsic calibration. The computer-implemented method for extrinsic calibration of one or more cameras with respect to a reference coordinate system comprises obtaining one or more images from one or more cameras, with each camera having a field of view, wherein each image shows an observation of at least one marker of a plurality of markers, wherein the plurality of markers are co-planar with respect to a reference plane, estimating, for the one or more cameras, a transformation between a respective camera coordinate system and the reference coordinate system based on an estimated pose of the at least one marker observed in the field of view of the camera relative to the camera coordinate system, estimating a pose of the reference plane with respect to the respective one or more camera coordinate systems based on a pre-defined or estimated pose of the reference plane with respect to the reference coordinate system and based on the estimated transformations between the one or more camera coordinate systems and the reference coordinate system, estimating planar poses of the plurality of markers with respect to the reference plane, and simultaneously adjusting the planar poses of the plurality of markers and the pose of the reference plane with respect to the respective one or more camera coordinate systems by iteratively reducing an error between a reprojection of the plurality of markers into the respective one or more camera coordinate systems and the position of the respective markers in the images.