Curved colour markers improve camera roll angle measurement on cylinders
Curvature as a Baseline: Monocular Pose Measurement of Cylindrical Objects with Dual Colour Stripe Markers
Computer Vision and Pattern Recognition
Summary
Measuring the exact position and rotation of thin cylindrical objects using one camera is hard because they have little flat space for markers. The authors show that by putting special two-colour stripes around the curved surface of a cylinder, the camera can better figure out how much the cylinder is rotated around its own axis. Using the natural curve of the object as part of the marker design greatly reduces errors in measurement compared to flat markers. Their math and simulations explain why curved markers work better and help guide how to design them.
What this means in practice
- •For robotics engineers: Measure rotation of cylindrical parts precisely with one camera using curved colour stripe markers to improve robotic grasping and manipulation.
- •For quality control teams: Inspect thin cylindrical products for correct orientation efficiently by using dual-colour curved markers to reduce measurement errors with a single camera setup.
Authors
Jaesung Hong, Dong Won Lee
Abstract
Thin cylindrical objects offer little space for planar markers. We propose a dual-colour-stripe marker that uses the known curvature of an object to improve pose measurement with a single camera. The boundary between two colours provides a long centre line, while dots and printed edges supply features at different depths. We analyse how this depth separation improves the estimation of rotation about the cylinder axis, or roll. For a camera-facing marker at 15 cm, the Cramér-Rao lower bound on roll standard deviation is 2.00°for a flat marker, 0.38°for a single curved marker and 0.21°for a wrap-around marker. Monte Carlo roll RMS errors are within about 10% of the corresponding standard-deviation bounds. A first-order relation connects the sagitta of the curved marker to the roll sensitivity provided by a stereo baseline. The analytical and simulation results explain how curvature improves monocular measurement and provide a basis for designing marker geometry.