Assessment and Improvement of Distance Measurement Accuracy for Time-of-Flight Cameras

Abstract

Time-of-flight depth cameras are interesting sensors for contact-less 3-D metrology because they combine mechanical robustness with independence of ambient lighting conditions. Their actual performance depends on many factors and is hard to predict from data sheets. In this study, we investigate the deviations of the distance measurements of a high-end phase-based depth camera. We focus on the impact of: 1) self-warming and external temperature; 2) on range noise as a function of distance and acquisition time; and 3) on distance-dependent biases. We present the dedicated experimental setups comprising a climate chamber, a calibration bench with a reference interferometer, and a laser tracker that provides controlled conditions and ground-truth data. These setups allow investigating the absolute accuracy and mitigating repeatable distance biases by adapting the measurement model based on experimental data. For demonstration, we apply the investigation to two state-of- the-art industrial depth cameras of the same brand and type (Helios Lucid), showing significantly different response to external temperature but similar distance-dependent biases. We adapt the measurement model of one of the cameras for distance-dependent inter-pixel biases and demonstrate that the resulting parameters reduce also the distance biases of the other camera by about 80% to less than 1 mm at ranges of up to 1 m. This indicates the potential for batch error compensation. This article contributes to better understanding distance deviations of depth cameras and to improving the accuracy of such cameras.