A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> We present an eye tracking algorithm which is robust against variations in scale, orientation and changes of eye appearances, such as eye blinking. The locations of the eye regions in the different frames are found using template matching. The method is kept invariant for rotations and scale by exploiting temporal information and by using a codebook of eye templates the method is robust against changes in eye region appearances. The entries of the codebook are generated automatically during the tracking of the eye regions and eventually represent a distinct set of eye appearances. Classification into different eye gestures, like blinking or different gaze directions, seems possible using these automatically learned patterns. <s> BIB001 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> A first proof of concept was developed for a head-mounted video camera system that is continuously aligned with the user's orientation of gaze. Eye movements are tracked by video-oculography and used as signals to drive servo motors that rotate the camera. Thus, the sensorimotor output of a biological system for the control of eye movements - evolved over millions of years s used to move an artificial eye. All the capabilities of multi-sensory processing for eye, head, and surround motions are detected by the vestibular, visual, and somatosensory systems and used to drive a technical camera system. A camera guided in this way mimics the natural exploration of a visual scene and acquires video sequences from the perspective of a mobile user, while the vestibulo-ocular reflex naturally stabilizes the "gaze-in-space" of the camera during head movements and locomotion. Various applications in health care, industry, and research are conceivable. <s> BIB002 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Eye tracking has long held the promise of being a useful methodology for human computer interaction. However, a number of barriers have stood in the way of the integration of eye tracking into everyday applications, including the intrusiveness, robustness, availability, and price of eye-tracking systems. To lower these barriers, we have developed the openEyes system. The system consists of an open-hardware design for a digital eye tracker that can be built from low-cost off-the-shelf components, and a set of open-source software tools for digital image capture, manipulation, and analysis in eye-tracking applications. We expect that the availability of this system will facilitate the development of eye-tracking applications and the eventual integration of eye tracking into the next generation of everyday human computer interfaces. We discuss the methods and technical challenges of low-cost eye tracking as well as the design decisions that produced our current system. <s> BIB003 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> This paper presents a new high-speed head- mounted binocular eye position measurement system using infrared lighting and image processing technology. Current eye tracking systems either run on-line at a lower speed, do the processing off-line, or use dedicated hardware to reach high on-line processing rates. The eye position measurement system we developed only uses a general-purpose computing system and off-the-shelf imaging devices. The binocular system can provide on-line horizontal and vertical measurement at a speed of 150 Hz on a desktop system with a 3 GHz Pentium processor. We report a novel dual-mode software system and a two-step processing algorithm to increase the processing rate. A symmetric mass center algorithm is designed to provide more accurate measurements when the pupil area is partially occluded. Using synthetic eye images, we show that our algorithm performs consistently better than some of the widely used algorithms in industry. <s> BIB004 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Gaze tracking technology is a convenient interfacing method for mobile devices. Most previous studies used a large-sized desktop or head-mounted display. In this study, we propose a novel gaze tracking method using an active appearance model (AAM) and multiple support vector regression (SVR) on a mobile device. Our research has four main contributions. First, in calculating the gaze position, the amount of facial rotation and translation based on four feature values is computed using facial feature points detected by AAM. Second, the amount of eye rotation based on two feature values is computed for measuring eye gaze position. Third, to compensate for the fitting error of an AAM in facial rotation, we use the adaptive discrete Kalman filter (DKF), which applies a different velocity of state transition matrix to the facial feature points. Fourth, we obtain gaze position on a mobile device based on multiple SVR by separating the rotation and translation of face and eye rotation. Experimental results show that the root mean square (rms) gaze error is 36.94 pixels on the 4.5-in. screen of a mobile device with a screen resolution of 800×600 pixels. <s> BIB005 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> In this work, we present an interactive optical see-through HMD (head-mounted device) which makes use of a user's gaze information for the interaction in the AR (augmented reality) environment. In particular, we propose a method to employ a user's half-blink information for more efficient interaction. As the interaction is achieved by using a user's eye gaze and half-blink information, the proposed system can provide more efficient computing environment. In addition, the proposed system can be quite helpful to those who have difficulties in using conventional interaction methods which use hands or feet. The experimental results present the robustness and efficiency of the proposed system. <s> BIB006 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> In driver assistance system, human eye gaze direction is an important feature described some driver's situation such as distraction and fatigue. This paper proposes a method to track driver's gaze direction by using deformable template matching. The method is divided into three steps: first, identifying the face area. Second, localizing the eye area. Finally, combining the eye region model and sight algorithm to determine the driver's gaze direction. Experimental results show that this method can effectively identify human's eye and track gaze motion in a real-time running basis. <s> BIB007 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Gaze tracking is to detect the position a user is looking at. Most research on gaze estimation has focused on calculating the X, Y gaze position on a 2D plane. However, as the importance of stereoscopic displays and 3D applications has increased greatly, research into 3D gaze estimation of not only the X, Y gaze position, but also the Z gaze position has gained attention for the development of next-generation interfaces. In this paper, we propose a new method for estimating the 3D gaze position based on the illuminative reflections (Purkinje images) on the surface of the cornea and lens by considering the 3D optical structure of the human eye model. This research is novel in the following four ways compared with previous work. First, we theoretically analyze the generated models of Purkinje images based on the 3D human eye model for 3D gaze estimation. Second, the relative positions of the first and fourth Purkinje images to the pupil center, inter-distance between these two Purkinje images, and pupil size are used as the features for calculating the Z gaze position. The pupil size is used on the basis of the fact that pupil accommodation happens according to the gaze positions in the Z direction. Third, with these features as inputs, the final Z gaze position is calculated using a multi-layered perceptron (MLP). Fourth, the X, Y gaze position on the 2D plane is calculated by the position of the pupil center based on a geometric transform considering the calculated Z gaze position. Experimental results showed that the average errors of the 3D gaze estimation were about 0.961 (0.48 cm) on the X-axis, 1.601 (0.77 cm) on the Y-axis, and 4.59 cm along the Z-axis in 3D space. & 2011 Elsevier Ltd. All rights reserved. <s> BIB008 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Abstract For an effective and efficient visual recognition system, the region-of-interest extraction of users is one of most important image processing duties. Generally, the position of the pupil in an eyeball is directly related to the user's interest in an input visual image. However, when using a monocular eye tracking system, it is not easy to discern an accurate position of the region-of-interest of the user in a three-dimensional space. In this paper, an eye tracking system based on binocular gaze detection is presented. The proposed system is designed as a wearable device with three mini-cameras and two hot-mirrors for users to see through. The two eye monitoring system acquires the pupil images of both eyes through the hot-mirrors illuminated by infrared LEDs; the front-view camera acquires the image visible to the user. The experiment results show that the proposed system improves upon the region-of-interest localization error of the users in both the horizontal and vertical directions for the front-view images acquired by the user. Through the proposed system, it became possible to accurately extract the user's region-of-interest, and so can be used to improve the image processing speed through focused information processing for the region-of-interest and narrow the selective information acquisition needed for users. <s> BIB009 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Eye movements are highly correlated with motor intentions and are often retained by patients with serious motor deficiencies. Despite this, eye tracking is not widely used as control interface for movement in impaired patients due to poor signal interpretation and lack of control flexibility. We propose that tracking the gaze position in 3D rather than 2D provides a considerably richer signal for human machine interfaces by allowing direct interaction with the environment rather than via computer displays. We demonstrate here that by using mass-produced video-game hardware, it is possible to produce an ultra-low-cost binocular eye-tracker with comparable performance to commercial systems, yet 800 times cheaper. Our head-mounted system has 30 USD material costs and operates at over 120 Hz sampling rate with a 0.5‐1 degree of visual angle resolution. We perform 2D and 3D gaze estimation, controlling a real-time volumetric cursor essential for driving complex user interfaces. Our approach yields an information throughput of 43 bits s −1 , more than ten times that of invasive and semi-invasive brain‐machine interfaces (BMIs) that are vastly more expensive. Unlike many BMIs our system yields effective real-time closed loop control of devices (10 ms latency), after just ten minutes of training, which we demonstrate through a novel BMI benchmark—the control of the video arcade game ‘Pong’. (Some figures may appear in colour only in the online journal) <s> BIB010 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> We present a new system that assists people's reading activity by combining a wearable eye tracker, a see-through head mounted display, and an image based document retrieval engine. An image based document retrieval engine is used for identification of the reading document, whereas an eye tracker is used to detect which part of the document the reader is currently reading. The reader can refer to the glossary of the latest viewed key word by looking at the see-through head mounted display. This novel document reading assist application, which is the integration of a document retrieval system into an everyday reading scenario for the first time, enriches people's reading life. In this paper, we i) investigate the performance of the state-of-the-art image based document retrieval method using a wearable camera, ii) propose a method for identification of the word the reader is attendant, and iii) conduct pilot studies for evaluation of the system in this reading context. The results show the potential of a document retrieval system in combination with a gaze based user-oriented system. <s> BIB011 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Unlike conventional portable eye-tracking methods that estimate the position of the mounted camera using 2-D image coordinates, the techniques that are proposed here present richer information about person's gaze when moving over a wide area. They also include visualizing scanpaths when the user with a head-mounted device makes natural head movements. We employ a Visual SLAM technique to estimate the head pose and extract environmental information. When the person's head moves, the proposed method obtains a 3-D point-of-regard. Furthermore, scanpaths can be appropriately overlaid on image sequences to support quantitative analysis. Additionally, a 3-D environment is employed to detect objects of focus and to visualize an attention map. <s> BIB012 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> In this work, a new head mounted eye tracking system is presented. Based on computer vision techniques, the system integrates eye images and head movement, in real time, performing a robust gaze point tracking. Nystagmus movements due to vestibulo-ocular reflex are monitored and integrated. The system proposed here is a strongly improved version of a previous platform called HATCAM, which was robust against changes of illumination conditions. The new version, called HAT-Move, is equipped with accurate inertial motion unit to detect the head movement enabling eye gaze even in dynamical conditions. HAT-Move performance is investigated in a group of healthy subjects in both static and dynamic conditions, i.e. when head is kept still or free to move. Evaluation was performed in terms of amplitude of the angular error between the real coordinates of the fixed points and those computed by the system in two experimental setups, specifically, in laboratory settings and in a 3D virtual reality (VR) scenario. The achieved results showed that HAT-Move is able to achieve eye gaze angular error of about 1 degree along both horizontal and vertical directions <s> BIB013 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> In this paper, we present an innovative approach to design a gazecontrolled Multimedia User Interface for modern, immersive headsets. The wide-spread availability of consumer grade Virtual Reality Head Mounted Displays such as the Oculus RiftTM transformed VR to a commodity available for everyday use. However, Virtual Environments require new paradigms of User Interfaces, since standard 2D interfaces are designed to be viewed from a static vantage point only, e.g. the computer screen. Additionally, traditional input methods such as the keyboard and mouse are hard to manipulate when the user wears a Head Mounted Display. We present a 3D Multimedia User Interface based on eye-tracking and develop six applications which cover commonly operated actions of everyday computing such as mail composing and multimedia viewing. We perform a user study to evaluate our system by acquiring both quantitative and qualitative data. The study indicated that users make less type errors while operating the eye-controlled interface compared to using the standard keyboard during immersive viewing. Subjects stated that they enjoyed the eye-tracking 3D interface more than the keyboard/mouse combination. <s> BIB014 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> In the last few years, the advancement of head mounted display technology and optics has opened up many new possibilities for the field of Augmented Reality. However, many commercial and prototype systems often have a single display modality, fixed field of view, or inflexible form factor. In this paper, we introduce Modular Augmented Reality (ModulAR), a hardware and software framework designed to improve flexibility and hands-free control of video see-through augmented reality displays and augmentative functionality. To accomplish this goal, we introduce the use of integrated eye tracking for on-demand control of vision augmentations such as optical zoom or field of view expansion. Physical modification of the device's configuration can be accomplished on the fly using interchangeable camera-lens modules that provide different types of vision enhancements. We implement and test functionality for several primary configurations using telescopic and fisheye camera-lens systems, though many other customizations are possible. We also implement a number of eye-based interactions in order to engage and control the vision augmentations in real time, and explore different methods for merging streams of augmented vision into the user's normal field of view. In a series of experiments, we conduct an in depth analysis of visual acuity and head and eye movement during search and recognition tasks. Results show that methods with larger field of view that utilize binary on/off and gradual zoom mechanisms outperform snapshot and sub-windowed methods and that type of eye engagement has little effect on performance. <s> BIB015 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Properly calibrating an optical see-through head-mounted display (OST-HMD) and maintaining a consistent calibration over time can be a very challenging task. Automated methods need an accurate model of both the OST-HMD screen and the user's constantly changing eye-position to correctly project virtual information. While some automated methods exist, they often have restrictions, including fixed eye-cameras that cannot be adjusted for different users.To address this problem, we have developed a method that automatically determines the position of an adjustable eye-tracking camera and its unconstrained position relative to the display. Unlike methods that require a fixed pose between the HMD and eye camera, our framework allows for automatic calibration even after adjustments of the camera to a particular individual's eye and even after the HMD moves on the user's face. Using two sets of IR-LEDs rigidly attached to the camera and OST-HMD frame, we can calculate the correct projection for different eye positions in real time and changes in HMD position within several frames. To verify the accuracy of our method, we conducted two experiments with a commercial HMD by calibrating a number of different eye and camera positions. Ground truth was measured through markers on both the camera and HMD screens, and we achieve a viewing accuracy of 1.66 degrees for the eyes of 5 different experiment participants. <s> BIB016 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Eye tracking technology in a head-mounted display has undergone rapid advancement in recent years, making it possible for researchers to explore new interaction techniques using natural eye movements. This paper explores three novel eye-gaze-based interaction techniques: (1) Duo-Reticles, eye-gaze selection based on eye-gaze and inertial reticles, (2) Radial Pursuit, cluttered-object selection that takes advantage of smooth pursuit, and (3) Nod and Roll, head-gesture-based interaction based on the vestibulo-ocular reflex. In an initial user study, we compare each technique against a baseline condition in a scenario that demonstrates its strengths and weaknesses. <s> BIB017 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> We introduce FaceVR, a novel method for gaze-aware facial reenactment in the Virtual Reality (VR) context. The key component of FaceVR is a robust algorithm to perform real-time facial motion capture of an actor who is wearing a head-mounted display (HMD), as well as a new data-driven approach for eye tracking from monocular videos. In addition to these face reconstruction components, FaceVR incorporates photo-realistic re-rendering in real time, thus allowing artificial modifications of face and eye appearances. For instance, we can alter facial expressions, change gaze directions, or remove the VR goggles in realistic re-renderings. In a live setup with a source and a target actor, we apply these newly-introduced algorithmic components. We assume that the source actor is wearing a VR device, and we capture his facial expressions and eye movement in real-time. For the target video, we mimic a similar tracking process; however, we use the source input to drive the animations of the target video, thus enabling gaze-aware facial reenactment. To render the modified target video on a stereo display, we augment our capture and reconstruction process with stereo data. In the end, FaceVR produces compelling results for a variety of applications, such as gaze-aware facial reenactment, reenactment in virtual reality, removal of VR goggles, and re-targeting of somebody's gaze direction in a video conferencing call. <s> BIB018 </s> A Review and Analysis of Eye-Gaze Estimation Systems, Algorithms and Performance Evaluation Methods in Consumer Platforms <s> C. Head-mounted setups <s> Gaze detection in Virtual Reality systems is mostly performed using eye-tracking devices. The coordinates of the sight, as well as other data regarding the eyes, are used as input values for the applications. While this trend is becoming more and more popular in the interaction design of immersive systems, most visors do not come with an embedded eye-tracker, especially those that are low cost and maybe based on mobile phones. We suggest implementing an innovative gaze estimation system into virtual environments as a source of information regarding users intentions. We propose a solution based on a combination of the features of the images and the movement of the head as an input of a Deep Convolutional Neural Network capable of inferring the 2D gaze coordinates in the imaging plane. <s> BIB019
Head mounted gaze trackers are portable platforms with applications ranging from computer input, interactions in virtual environments, gaming controls, augmented reality and neuro/psychological research. The general setup includes two cameras; one (eye camera) pointed at the wearer's eye, to detect the pupil; and the other (scene camera) capturing the wearer's point of view, with sometimes additional components like NIR light sources and hot mirrors. Head-mounted gaze trackers have been implemented as attachment-free, mobile, low-cost, lightweight devices with simple hardware and software. Also they are known to provide high accuracy gaze information in unconstrained settings. 3D gaze estimation with head-mounted trackers have been reported in several papers including BIB013 , BIB008 - BIB012 . Algorithms for high accuracy and 3D eye tracking proposed by Park BIB008 are based on 3D human eye model and Purkinje images. Pupil size and Purkinje images are fed as inputs to a multi-layer perceptron to estimate the depth location of gaze followed by 2D gaze coordinates. Takamatsu BIB012 describes a Visual SLAM technique to estimate the user head pose and determine 3D point of regard of the user. It also includes a 3D environment to detect objects of focus and visualization of a 3D attention map in a real environment. Lanata BIB013 presents a stereo-vision based method that implements a novel binocular system comprising of two mapping functions: linear and quadratic for depth estimation of gaze locations in 3D space. The performance compared to other 3D methods show significant improvement in accuracy. In BIB009 , 3D gaze tracking with multiple calibration planes is implemented with a single eye view camera and four IR markers. The system operates in monocular and binocular mode independently. A low-cost 3D eye tracking solution is provided by BIB010 in which images from two eye cameras are used with intensity thresholding and blob-contour detection to determine pupil center coordinates. The 2D gaze location is then obtained by polynomial mapping and 3D gaze is obtained from the meeting point of the gaze vectors of both eyes. 2D methods and applications with head-mounted eye tracking have been proposed in a several works.  reports an ultra-low cost 2 camera based gaze tracking system that is easy to assemble and aligns scene and eye videos by using synchronized flashing lights. A novel smooth-pursuit-based calibration methodology is proposed that works with pupil detection to track gaze. A new high speed binocular eye localization scheme using simple components was proposed by Kiderman BIB004 using two cameras and two hot mirrors. It shows speed advancement over contemporary slow systems that do offline processing. Other advanced methods are proposed in Schneider & Bartl BIB002 where a head mounted camera system tracks and follows the user's gaze direction for natural exploration of a visual scene by capturing the perspective of the mobile user. Applications of this system include documentation of medical processes, sports etc. In Virtual and Augmented reality (VR and AR respectively) research, gaze tracking and gaze based functions are used to make the user experiences more immersive, natural and user interactions fast and efficient in a VR/AR environment. Applications for Augmented Reality are described in Choi BIB006 where the device uses a scene camera and eye tracker to estimate user gaze and blink-state for interacting with the AR environment. A head mounted system that employs gaze tracking for immersive and realistic gaming experience is proposed by Park BIB005 where cursor aiming in the gaming environment is controlled by gaze tracking. A wearable gaze tracking device for determining effectiveness of text layout and line spacing for analyzing reading behavior is described in Dengel BIB011 . Parkhurst and Babcock BIB003 presents the development of a head mounted system called OpenEyes with open hardware and software tools for gaze tracking. Several types of eye and head gestures, such as saccades, smooth pursuit and nod-roll are studied in BIB017 BIB007 1 camera 85% None BIB001 Image frames 4.5 pixels None display coupled with an eye tracker is used to study which of these gestures result in better user experience in a VR environment. A facial re-enactment method for gaze aware VR system is presented in BIB018 . It does real time facial motion capture of a user wearing an HMD along with monocular eye tracking. The purpose is to achieve real time photo-realistic rendering of face and eye appearances as users change facial expressions and gaze directions. Gaze is estimated from images taken using monocular camera and IR LEDs using a hierarchical classification method. In BIB014 eye tracking is used to develop an immersive 3D user interface for VR and implement several multimedia applications along with usability testing. Eye gaze pattern is extracted along with fixations to implement 3D virtual menu selection and eye based typing for mail composition using a virtual keyboard. A saliency based gaze localization approach using deep learning has been proposed in BIB019 . In this, image features and head movements are inputs to a convolutional neural network to estimate gaze coordinates in a VR system. To make eye tracking in HMD systems flexible with respect to various users, HMD drifts and tracker camera adjustments, BIB016 presents a method for automatic calibration of the eye camera in the HMD. With this, the users need not maintain a fixed head pose and relative movements of HMD and eye camera can be tolerated for reliable eye tracking.  makes use of gaze, dwell time and half blink information for the purpose of hands-free object selection with an optical see through head mounted AR device. The multiple input parameters are used to avoid accidental/unintentional selection of items. Pupil motion is tracked to estimate a user's viewing point, with dwell time and half blink detection successively used for the object selection process. Kalman filtering is used minimize pupil jitter and drifts. The gaze tracking accuracy of the system is reported to improve with more calibration points with the best being 0.39 degrees. An innovative AR application combining eye tracking with a smartwatch for implementing a wearable context aware messaging service is done in  . A head-mounted eye tracker estimates the gaze and together with data from a scene camera it is used to track where the user is looking in the real world. The smartwatch works as a message input and output device in conjunction with the tracking device to embed/display messages with the "augmented objects. An AR application for reading and document retrieval using a headmounted eye tracker along with a see through display is shown in BIB011 . Eye tracking helps to estimate the section of the document the reader is focused into, in real time. Associated information on the specific part of the document is retrieved and displayed on the HMD. A calibration procedure for the HMD is also mentioned. In this, a user is presented with several dots in the HMD and he/she has to click the position of each dot in a calibration window. The homography between the scene image and the HMD is then estimated to map the gaze position on the scene to that on the HMD. The system achieves accuracy sufficient to distinguish between alternate lines in a document. A hardware and software framework for AR displays implementing eye tracking and gaze based interactions can be found in BIB015 . In this, a see through HMD is integrated with stereo eye tracking and configurable optics for various see through configurations. The system is designed to have on demand zoom and FOV expansion in a see through AR system. Eye related parameters like gaze, squint and blinks are tracked for activating different functions such as binary, sub-regional and gradual zoom and capturing snapshots of the AR view.