# Presenting a Human Pupil Orbit Model (HPOM) for Eye-Gaze Tracking
## 1 Introduction  
Eye tracking technology detects the direction of a user's gaze in real time. This technology is used in various fields, such as for analysing user emotions and behaviour by, for example, analysing how long a subject's gaze remains looking in a specific direction or how the gaze may follow a certain path of movement [1, 2]. In addition, this technology can be applied to daily life, such as configuring a smart home environment to combine a human interface device with Internet of Things technology to control various devices such as personal computers or smart televisions [3, 4]. Further, various studies are being conducted by applying eye tracking technology in the medical field. A representative example is the video-oculography developed by [PERSON] for the purpose of research on small eye movements and visual exploration of objects and scenes [5]. This technology has been differentiated into various fields and, in recent years, research has been conducted to predict eye movement diseases [6]. In addition, it has been applied to diagnostic equipment such as fundus cameras and magnetic resonance imaging [7, 8]. Recently, with the development of the metaverse technologies such as virtual reality, augmented reality, and extended reality, research has been conducted for convergence with reality in various fields [9]. In particular, research is being combined to project physical activity in the real world onto the metaverse such as motion-tracking and eye-tracking technologies [10, 11, 12, 13]. There are two main types of eye-gaze tracking technologies. One uses electrodes and the other uses cameras. The electrode method uses biosignal processing by attaching sensors around the eyes and acquiring an electronic signal representing eye movements [14]. The other method uses a camera by either recording a close-up of the subject's eyes or by photographing the whole front of their face then analysing these images. One method that is able to track the gaze from close to the eye, uses a smart lens from which laser light is emitted, and another method uses the position of any glint created in the eye by a near-infrared light source attached to glasses the user wears [15; 16]. Using cameras that record the entire front of the face has been studied as a method of tracking gaze, which is achieved by analysing the shape of the pupil or iris using certain image processing technique from the recorded images [17; 18; 19]. Furthermore, research has been conducted into a method of tracking the gaze using the glint that reflects due to a light source directed at the iris [20; 21; 22; 23; 24]. As such, the eye-tracking research area has been a subject of continuous research to find a method to improve accuracy. The problem has previously been tackled using various sensors, structures, and phenomena. However, these studies are all limited in that the eye's ocular rotational centre point (ORCP) cannot be found. For this reason, various methods considering ORCP have been proposed, and studies that directly estimating 3D pose of the eyeball in the camera scene using the facial-model and the eyeball-model have been mainly conducted [25; 26; 27; 28]. Recently, an improved method of fitting an eye model by analysing the shape of the pupil in 3D space has been proposed [29]. This approach was taken with a view to applying it to a head-mounted eye tracker system where the distance between the camera and the eye was very close due to the head-mounted design. In this paper, we propose a novel pre-processing method for eye-gaze tracking based on recording the front of the face that works regardless of the distance the camera is placed from the eye. This innovative process occurs in between acquiring the pupil shape and making the final eye gaze direction determination. The proposed method acquires a set of points locating the pupil in three-dimensional coordinate space. We named the model for acquiring these set of points the Human Pupil Orbit Model (HPOM).