# A Method of Free-Space Point-of-Regard Estimation Based on 3D Eye Model and Stereo Vision
## 5 Conclusions  
In this paper, a simplified 3D eye model is used to realize 3D point-of-regard (PoR) estimation in free space, and the method is proven by experiments. We also analyze the application potential of this method in the head-mounted gaze tracking device, and propose a corresponding structure of a novel gaze tracking system.  
The proposed gaze tracking system is constituted by three pairs of stereo cameras. In Sections 3.1 and 3.2, we describe the features of the semi-transparent mirror and the layout of the cameras. The system structure proposed in this paper has the ability to obtain clearer images. Camera calibration and system coordinate system determination are simpler than the previous methods. Clear images also make the extraction of pupil and inner eye corner more accurate from the image.  
In Section 3.3, we focus on describing the 3D PoR estimation model and personal calibration process carried out by the system. The personal calibration process of the system is based on the geometric model adopted by the system. We take full account of reducing the complexity of personal utilization, and reduce the number of personal eyeball parameters to be calibrated to two types. This makes the proposed method not only ensure certain accuracy, but also reduce the user's operation steps as much as possible. Moreover, the validity of calibration process is verified by experiments.  
We evaluated the whole method by free observation experiments. Experimental results show that this method can be applied to real scenes and has sufficient accuracy under indoor environment. This method has the potential to be applied to wearable devices. The purpose of further improving its  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Unit: cm** & **0.8 m** & **1.5 m** & **2 m** & **2.5 m** & **3 m** & **4 m** \\ \hline Error on X & 0.4 \(\pm\) 0.4 & 0.6 \(\pm\) 0.4 & 0.7 \(\pm\) 0.6 & 0.9 \(\pm\) 0.6 & 0.9 \(\pm\) 0.5 & 1.3 \(\pm\) 0.9 \\ Error on Y & 0.4 \(\pm\) 0.3 & 0.6 \(\pm\) 0.5 & 0.7 \(\pm\) 0.4 & 0.8 \(\pm\) 0.6 & 1.0 \(\pm\) 0.6 & 1.3 \(\pm\) 1.1 \\ Error on Z & 3.3 \(\pm\) 2.7 & 4.2 \(\pm\) 3.1 & 5.3 \(\pm\) 4.0 & 7.6 \(\pm\) 6.1 & 8.8 \(\pm\) 6.3 & 10.7 \(\pm\) 8.5 \\ Overall & 3.4 \(\pm\) 2.7 & 4.3 \(\pm\) 3.1 & 5.4 \(\pm\) 4.1 & 7.8 \(\pm\) 6.1 & 8.9 \(\pm\) 6.4 & 10.8 \(\pm\) 8.5 \\ Overall in [32] & 2.1 \(\pm\) 0.3 & / & 3.6 \(\pm\) 0.3 & / & 5.7 \(\pm\) 0.5 & / \\ \hline \end{tabular}
\end{table}
Table 1: Average errors in centimeters at different distances of our method and the comparison with the method in [32].  
accuracy is to enable such device to be applied to the spots of industry to assist workers in controlling automated equipment in workshops.  
All authors were involved in the research of this article. [PERSON] proposed the algorithms, design the experiments, analyzed the experimental data, and wrote this paper; [PERSON] designed the gaze tracking device and guided the research group; and [PERSON] and [PERSON] carried out the calibration experiments. All authors reviewed and approved the manuscript.  
This research was funded by National Natural Science Foundation of China, grant number 51575388.  
The authors declare no conflict of interest.