Search

Cornea radius estimation is a key technique for 3D gaze estimation in the single-camera 3D gaze tracking system. Traditional methods with one-camera-one-light-source systems or one-camera-two-light-source systems cannot achieve 3D gaze estimation. The 3D line-of-sight can be estimated only when the cornea radius is pre-calibrated by the user. A cornea radius calibration method based on the iris radius is proposed in this paper for 3D gaze estimation in remote one-camera-two-light-source systems. We first calibrate the iris radius based on the binocular strategy, estimate the spatial iris center using the calibrated iris radius, and then calibrate the cornea radius by a set of non-linear equations under the constraint of equivalent distances from the cornea center to the iris edge points. The calibrated cornea radius is verified by binocular optimization constraints. Simulations and physical experiments validate the effectiveness of the proposed method. The iris-based cornea radius calibration approach is novel; it can be used to obtain the cornea radius and 3D gaze using remote one-camera-one-light-source or one-camera-multi-light-source systems.

Eye movements play a very significant role in human–computer interaction (HCI) as they are natural and fast, and contain important cues for human cognitive state and visual attention. Over the last two decades, many techniques have been proposed to accurately estimate the gaze. Among these, video-based remote eye trackers have attracted much interest, since they enable nonintrusive gaze estimation. To achieve high estimation accuracies for remote systems, user calibration is inevitable in order to compensate for the estimation bias caused by person-specific eye parameters. Although several explicit and implicit user calibration methods have been proposed to ease the calibration burden, the procedure is still cumbersome and needs further improvement. In this paper, we present a comprehensive analysis of regression-based user calibration techniques. We propose a novel weighted least squares regression-based user calibration method together with a real-time cross-ratio based gaze estimation framework. The proposed system enables to obtain high estimation accuracy with minimum user effort, which leads to user-friendly HCI applications. Experimental results conducted on both simulations and user experiments show that our framework achieves a significant performance improvement over the state-of-the-art user calibration methods when only a few points are available for the calibration.

A novel flow measurement principle is presented enabling non-intrusive volume flow measurements of liquids in the ml/min range. It is based on an opto-acoustical time-of-flight principle, where the time interval is recorded in which a thermal label travels a known distance through a flow channel. Big advantages are the insensitivity to temperature drift and the fact that user calibration is unnecessary. The paper presents a set of physics-based criteria that define the working range of the measurement principle. A prototype of a flow meter was developed and evaluated in a test rig with flows of water, isopropyl alcohol (IPA) and mixtures of both liquids. Pure water and IPA flows of 0.1 to 2 ml min-1 were measured and found to coincide with the reference flows within 4%. The root-mean-square (RMS) value of the fluctuations did not exceed 3%. For flows of 2 ml min-1 the limited power of the laser source caused deviations of 7% with 5% fluctuations. Finally, flow measurements were done in water-IPA mixtures with concentrations between 10% and 90%-w/w at a flow rate of 15 g h-1 (≈0.3 ml min-1). The ratio of measured and reference flow appeared to be 4% to 5% below the theoretical value, but it was hardly a function of mixture composition. Hence, liquid independence of the measurement principle was proven. © 2010 IOP Publishing Ltd.