A Taxonomy and Analysis of Camera Calibration Methods for Traffic Monitoring Applications

Abstract

Abstract-Many vision-based automatic traffic monitoring systems require a calibrated camera for computing speeds and length-based classifications of tracked vehicles. A number of techniques, both manual and automatic, have been proposed for performing such calibration, but no study has yet focused upon evaluating the relative strengths of these different alternatives. We present a taxonomy for roadside camera calibration that not only encompasses the existing methods (VVW, VWH, and VWL) but also includes several novel ones as well (VVH, VVL, VLH, VVD, VWD, and VHD). We also introduce an overconstrained approach that takes into account all the available measurements, resulting in reduced error as well as overcoming the inherent ambiguity in the single-vanishing-point solutions. This important but oft-neglected ambiguity has not received the attention that it deserves; we analyze it and propose several ways of overcoming it. Our analysis includes the relative tradeoffs between twovanishing-point solutions, single-vanishing-point solutions, and solutions that require the distance to the road to be known. The various methods are compared using simulations and experiments with real images, showing that methods that use a known length generally outperform the others in terms of error, and that the overconstrained method reduces errors even further.

Computer vision in roadway transportation systems: a survey

“…Additionally, such a system requires (1) an accurate camera calibration strategy that produces a geometric mapping for translating image pixel positions to real-world coordinates, [176][177][178][179][180][181][182][183][184] (2) an understanding of the impact of vehicle height on speed accuracy, 179,184,185 and (3) an accurate reference measurement system. 186 The geometric mapping is typically performed using a projective matrix transformation.…”

Precise Vehicle Speed Measurement Based on a Hierarchical Homographic Transform Estimation for Law Enforcement Applications

“…So far, vision-based measurement using driver assistance and traffic surveillance cameras have been well studied [2], [10], unlike the field of law enforcement cameras.…”

Automatic Single-View Calibration and Rectification from Parallel Planar Curves

“…Single-view methods typically rely upon prior knowledge of the features lying on these planar surfaces, such as straight lines or orthogonal structure (e.g., [1,2]). However these methods fail when orthogonal structure is not dominant in the image or when there are no straight lines from which to extract vanishing points.…”

“…Traffic surveillance is one of the main applications for automatic camera rectification [3,2]. Some methods [4,5] use vehicle trajectories in the image to estimate the ground plane orientation, however these have the disadvantage that recalibration after a PTZ shift may take considerable time if traffic is sparse.…”

“…Some methods [4,5] use vehicle trajectories in the image to estimate the ground plane orientation, however these have the disadvantage that recalibration after a PTZ shift may take considerable time if traffic is sparse. The majority of static methods assume that straight lines or rectangular patterns or textures are available for vanishing point estimation [2,6].…”