眼動儀是一種藉由追蹤使用者眼球運動並推估使用者凝視點的裝置，主要的用途在於心理學上的研究和做為身障者的輔具。一般的眼動儀在進行完校正步驟後，若是使用者頭部有移動，預估出的凝視點誤差將會增加，除了使用一些裝置固定頭部外，為了追求使用時的自由度和方便性，如何在頭部能夠移動的情況下進行正確的凝視點預估是眼動儀研究中相當重要的一部分，一般將這個問題稱為頭動補償。
在眼動儀的相關研究中，主要可以分為以二維映射函數預估凝視點、以光點相對位置預估凝視點及以三維眼球模型預估視軸三個大類，而根據不同的眼動儀架構有不同的頭動補償方法，也具有不同的優點和缺點。
本論文針對頭動補償的問題提出一個頭動補償機制，並將此機制實作，建立一套具有頭動補償模式的眼動儀系統，主要硬體為一個具有兩台攝影機的頭戴式眼動儀，除了具有頭動補償的模式外，也具備基本的無頭動補償模式和實景模式。
在頭動補償的機制部分，主要的方法是以實景攝影機偵測四張貼在螢幕上的圓形圖卡，計算螢幕的深度和三維位置；在校正時計算二維映射函數和校正平面，使用時利用映射函數和校正平面建立視軸，利用視軸和螢幕平面的資訊計算凝視點，結合三維座標和二維映射函數的概念進行頭動補償，減少因為頭部位移造成的誤差，從實驗結果來看，和文獻[35]相比，本論文系統中的頭動補償模式在使用者頭部移動下可以更減少0.5至1度的誤差。

關鍵字：眼動儀，頭動補償

Eye tracker is a device for measuring eye movements and estimating POG (Point of gaze). It is currently used in psychology field and also can be the assistive devices for disabled people. After calibration, if user’s head moves when using eye tracker, the error of POG will enlarge. An easy way to solving this problem is using some device to hold user’s head, but for pursue the freedom and comfort, how to estimate correct POG when head moving is one of important topics in eye tracker field. The topic is called head movement compensation.
There are three major methods of estimating POG in the related research. First, estimating POG by using 2D mapping function, second, estimating POG according to the relative position between light points reflect on eye ball and pupil center, third, building the 3D eye ball module to estimate visual axis and optical axis. There are many different ways of head movement compensation for each method of estimating POG, and they also have different advantages and disadvantages.
In this work, this paper presents an approach of head movement compensation and implement it. Build an eye tracker system has the ability of head movement compensation. In this system, the hardware this system using is a head mounted eye tracker has two cameras. Beside mode of head movement compensation, this system also has the basic modes like mode of no head movement and mode of real scene.
In the section of the approach of head movement compensation, this system uses scene camera to detect circular patterns pasted on monitor and estimate monitor’s depth and 3D position. When calibrating, get the information of mapping function and calibration plane, when using eye tracker, estimate visual axis by them and calculate POG, reduces the error caused by head movement. Compare with [35], The experiment result shows this approach can reduce 0.5~1゜degree error when user has large head movement.

Keywords:eye tracker, head movement compensation.

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