Practical calibration procedures for augmented reality

Extended-Reality Technologies: An Overview of Emerging Applications in Medical Education and Clinical Care.

Recupera algunos de los elementos menos estudiados y reconocidos en el ensayo latinoamericano: su profunda vocación de reflexión, diálogo y mediación intelectual; su plasticidad y apertura a la búsqueda del sentido; su vínculo con la sociabilidad, la conversación y la generación de un espacio simbólico de encuentro; su capa cidad de establecer una nueva retroalimentación entre lectura y escritura.

Inherent to the field of computer-aided surgery (CAS) is the necessity to handle sophisticated equipment in the operating room; an undesired side-effect of this development is the fact that the surgeon’s attention is drawn from the operating field since surgical progress is partially monitored on the computer’s screen. The overlay of computer-generated graphics over a real-world scene, also referred to as augmented reality (AR), provides a possibility to solve this problem. The considerable technical problems associated with this approach such as viewing of the scenery within a common focal range on the head-mounted display (HMD) or latency in display on the HMD have, however, kept AR from widespread usage in CAS. In this paper, the concept of the Varioscope AR, a lightweight head-mounted operating microscope used as a HMD, is introduced. The registration of the patient to the preoperative image data as well as preoperative planning take place on VISIT, a surgical navigation system developed at our hospital. Tracking of the HMD and stereoscopic visualisation take place on a separate POSIX.4 compliant realtime operating system running on PC hardware. While being in a very early stage of laboratory testing, we were able to overcome the technical problems described above; our work resulted in an AR visualisation system with an update rate of 6 Hz and a latency below 130 ms. First tests with 2D/3D registration have shown a match between 3D world coordinates and 2D HMD display coordinates in the range of 1.7 pixels. It integrates seamlessly into a surgical navigation system and provides a common focus for both virtual and real world objects. On the basis of our current results, we conclude that the Varioscope AR with the realtime visualisation unit is a major step towards the introduction of AR into clinical routine.

Augmented Reality (AR) is the process of integrating virtual elements in reality, often by mixing computer graphics into a live video stream of a real scene. It requires registration of the target object with respect to the cameras. To this end, some approaches rely on dedicated hardware, such as magnetic trackers or infra-red cameras, but they are too expensive and cumbersome to reach a large public. Others are based on specifically designed markers which usually look like bar-codes. However, they alter the look of objects to be augmented, thereby hindering their use in application for which visual design matters. Recent advances in Computer Vision have made it possible to track and detect objects by relying on natural features. However, no such method is commonly used in the AR community, because the maturity of available packages is not sufficient yet. As far as deformable surfaces are concerned, the choice is even more limited, mainly because initialization is so difficult. Our main contribution is therefore a new AR framework that can properly augment deforming surfaces in real-time. Its target platform is a standard PC and a single webcam. It does not require any complex calibration procedure, making it perfectly suitable for novice end-users. To satisfy to the most demanding application designers, our framework does not require any scene engineering, renders virtual objects illuminated by real light, and let real elements occlude virtual ones. To meet this challenge, we developed several innovative techniques. Our approach to real-time registration of a deforming surface is based on wide-baseline feature matching. However, traditional outlier elimination techniques such as RANSAC are unable to handle the non-rigid surface's large number of degrees of freedom. We therefore proposed a new robust estimation scheme that allows both 2–D and 3–D non-rigid surface registration. Another issue of critical importance in AR to achieve realism is illumination handling, for which existing techniques often require setup procedures or devices such as reflective spheres. By contrast, our framework includes methods to estimate illumination for rendering purposes without sacrificing ease of use. Finally, several existing approaches to handling occlusions in AR rely on multiple cameras or can only deal with occluding objects modeled beforehand. Our requires only one camera and models occluding objects at runtime. We incorporated these components in a consistent and flexible framework. We used it to augment many different objects such as a deforming T-shirt or a sheet of paper, under challenging conditions, in real-time, and with correct handling of illumination and occlusions. We also used our non-rigid surface registration technique to measure the shape of deformed sails. We validated the ease of deployment of our framework by distributing a software package and letting an artist use it to create two AR applications.

Augmented reality based applications have been experimented with in various contexts. Typically, the interaction is supported by handled devices, which, in specific scenarios, may hinder the interaction and spoil the experience of use, as the user is forced to hold the device and to keep her eyes on it at all times. The recent launch on the market of light-weight, unobtrusive head-mounted displays may change this circumstance. Nevertheless, investigations are needed to understand if such head-worn devices effectively outperform handheld devices in terms of comfort and pleasant experience of use. Here we present two experiments aimed at assessing the comfort of wearing a head-worn, see-through AR viewer in both a controlled and a natural setting. Besides the comfort of wearing the device, aspects related to the user experience were also investigated in the field evaluation. Our findings suggest that the head-mounted display examined is comfortable to wear regardless of the context of use. Interestingly in the field trails, participants did not express concern for the impression they would have made on other people and the experience of use was overall pleasant. Possible issues related to visual fatigue emerged.

One of the main problems of monoscopic video see-through augmented reality (AR) is the lack of reliable depth information. This makes it difficult to correctly represent complex spatial interactions between real and virtual objects, e.g., when rendering shadows. The most obvious graphical artifact is the incorrect display of the occlusion of virtual models by real objects. Since the graphical models are rendered opaquely over the camera image, they always appear to occlude all objects in the real environment, regardless of the actual spatial relationship. In this paper, we propose to utilize a new type of hardware in order to solve some of the basic challenges of AR rendering. We introduce a depth-of-flight range sensor into AR, which produces a 2D map of the distances to real objects in the environment. The distance map is registered with high resolution color images delivered by a digital video camera. When displaying the virtual models in AR, the distance map is used in order to decide whether the camera image or the virtual object is visible at any position. This way, the occlusion of virtual models by real objects can be correctly represented. Preliminary results obtained with our approach show that a useful occlusion handling based on time-of-flight range data is possible.

Since the recent slowdown in the smartphone market, studies for wearable devices are briskly being carried out to find new markets, such as virtual reality devices. In this paper, a head-mounted display (HMD) which provides expanded virtual images before human eyes by enlarging images of a small display was designed, and the tolerance analysis method for a focus-adjustable HMD based on afocal optical systems was studied. There are two types of HMDs: a see-through type that allows the user to view the surroundings, and a see-close type where the user can only view the display screen; the former is used in this study. While designing the system, we allowed a lens within the system to be shifted to adjust its focus from +1 to −4 D (diopters).The yield of the designed systems was calculated by taking the worst-case scenario of a uniform distribution into account. Additionally, a longitudinal aberration was used rather than MTF for the tolerance analysis with respect to system performance. The sensitivity of the designed system was calculated by assigning a certain tolerance, and the focus lens shift was calculated to adjust the image surface variations resulting from the tolerance. The smaller the tolerance, the more expensive the unit price of the products. Very small tolerances may even be impossible to fabricate. Considering this, the appropriate tolerance was assigned; the maximum shift of the focus lens in which the image surface can be adjusted was obtained to find the changes in aberration and a good yield.

In this article, we present a client/server augmented reality (AR) system for viewing complex assembly models on mobile phones. Complex model information is located on a PC which takes care of all of the heavy AR tracking and rendering computation. A camera phone is used as a client to show this information, augmented on still images as animated view. The mobile phone interface also supports correct masking of the assembly pieces as they come together, as well as a graphics only viewing mode intended for better understanding of the assembly process. In addition to describing the mobile augmented assembly system we present results from two pilot user studies evaluating elements of the user interface. INTRODUCTION In order to remain competitive, today’s industry is employing a growing number of product variations with shorter and shorter life cycles, requiring efficient ways to handle the production planning and processing. Assembly line workers face more and more complex tasks and an increasing memory load is posed by the new production needs. Experienced workers may be able to handle several product variants at the same time, but new workers require training and guidance to handle the work tasks. Related activities such as maintenance and repair also require a lot of know-how of complex products. Guidance in assembly tasks is commonly provided by using printed blueprints or other documents. However, these are mainly two dimensional images or text while the real assembly task is three dimensional, making the relationship between parts hard to understand. Computer based technologies have been developed such as electronic guides, multimedia training material and interactive documents. However, these typically require the user to turn away from the assembly task to study a computer screen separate from the workspace. In our research we explore how augmented reality (AR) technology can be used to provide more intuitive guides to assist with assembly, repair and training tasks. With AR technology, synthetic objects can be merged with the user’s view of the real world so that the user can perform the assembly task without needing to look at a separate screen. The virtual objects appear in the correct position so that AR enables the creation of realistic looking 3D animated assembly “manuals”. Other researchers have developed prototype AR systems for supporting assembly tasks. These are typically based on head mounted displays (HMDs) connected to desktop or wearable computers. However, wearable computers are relatively expensive, they have a short battery life, and taking them into a harsh industrial environment is not always possible. Head mounted displays can also be bulky, they involve safety issues, and many workers are reluctant to wear them. To overcome these disadvantages, we are interested in developing a reliable mobile phone based AR assembly system. Today’s mobile phones have fast processors, significant memory, 3D graphics support, and high resolution displays. They contain various accessories that can be used for developing mobile AR applications such as good quality cameras, connectivity by Bluetooth, WLAN and GPRS, and various SAM.700.003.1155

Computer visualization can effectively deliver instructions to a user whose task requires understanding of a real world scene. Consider the example of surgical telementoring, where a general surgeon performs an emergency surgery under the guidance of a remote mentor. The mentor guidance includes annotations of the operating field, which conventionally are displayed to the surgeon on a nearby monitor. However, this conventional visualization of mentor guidance requires the surgeon to look back and forth between the monitor and the operating field, which can lead to cognitive load, delays, or even medical errors. Another example is 3D acquisition of a real-world scene, where an operator must acquire multiple images of the scene from specific viewpoints to ensure appropriate scene coverage and thus achieve quality 3D reconstruction. The conventional approach is for the operator to plan the acquisition locations using conventional visualization tools, and then to try to execute the plan from memory, or with the help of a static map. Such approaches lead to incomplete coverage during acquisition, resulting in an inaccurate reconstruction of the 3D scene which can only be addressed at the high and sometimes prohibitive cost of repeating acquisition.Augmented reality (AR) promises to overcome the limitations of conventional out-of-context visualization of real world scenes by delivering visual guidance directly into the user's field of view, guidance that remains in-context throughout the completion of the task. In this thesis, we propose and validate several AR visual interfaces that provide effective visual guidance for task completion in the context of surgical telementoring and 3D scene acquisition.A first AR interface provides a mentee surgeon with visual guidance from a remote mentor using a simulated transparent display. A computer tablet suspended above the patient captures the operating field with its on-board video camera, the live video is sent to the mentor who annotates it, and the annotations are sent back to the mentee where they are displayed on the tablet, integrating the mentor-created annotations directly into the mentee's view of the operating field. We show through user studies that surgical task performance improves when using the AR surgical telementoring interface compared to when using the conventional visualization of the annotated operating field on a nearby monitor. A second AR surgical telementoring interface provides the mentee surgeon with visual guidance through an AR head-mounted display (AR HMD). We validate this approach in user studies with medical professionals in the context of practice cricothyrotomy and lower-limb fasciotomy procedures, and show improved performance over conventional surgical guidance. A comparison between our simulated transparent display and our AR HMD surgical telementoring interfaces reveals that the HMD has the advantages of reduced workspace encumbrance and of correct depth perception of annotations, whereas the transparent display has the advantage of reduced surgeon head and neck encumbrance and of annotation visualization quality. A third AR interface provides operator guidance for effective image-based modeling and rendering of real-world scenes. During the modeling phase, the AR interface builds and dynamically updates a map of the scene that is displayed to the user through an AR HMD, which leads to the efficient acquisition of a five-degree-of-freedom image-based model of large, complex indoor environments. During rendering, the interface guides the user towards the highest-density parts of the image-based model which result in the highest output image quality. We show through a study that first-time users of our interface can acquire a quality image-based model of a 13m $\times$ 10m indoor environment in 7 minutes.A fourth AR interface provides operator guidance for effective capture of a 3D scene in the context of photogrammetric reconstruction. The interface relies on an AR HMD with a tracked hand-held camera rig to construct a sufficient set of six-degrees-of-freedom camera acquisition poses and then to steer the user to align the camera with the prescribed poses quickly and accurately. We show through a study that first-time users of our interface are significantly more likely to achieve complete 3D reconstructions compared to conventional freehand acquisition. We then investigated the design space of AR HMD interfaces for mid-air pose alignment with an added ergonomics concern, which resulted in five candidate interfaces that sample this design space. A user study identified the aspects of the AR interface design that influence the ergonomics during extended use, informing AR HMD interface design for the important task of mid-air pose alignment.

Purpose Evacuation drills should be more realistic and interactive. Focusing on situational and audio-visual realities and scenario-based interactivity, the authors have developed a game-based evacuation drill (GBED) system that presents augmented reality (AR) materials on tablet computers. The paper's current research purpose is to improve visual reality (AR materials) in our GBED system. Design/methodology/approach The author's approach is to develop a new GBED system that superimposes digital objects [e.g. three-dimensional computer graphics (3DCG) elements] onto real-time vision using a marker-based AR library, a binocular opaque head-mounted display (HMD) and other current easily available technologies. Findings The findings from a trial experiment are that the new GBED system can improve visual reality and is appropriate for disaster education. However, a few problems remain for practical use. Research limitations/implications When using the GBED system, participants (i.e. HMD wearers) can suffer from 3D sickness and have difficulty in moving. These are important safety problems in HMD-based systems. Social implications The combination of AR and HMDs for GBEDs (i.e. integrating virtual and real worlds) will raise questions about its merits (pros and cons). Originality/value The originality of the research is the combination of AR and an HMD to a GBED, which has previously been realized primarily as simulation games in virtual worlds. The authors believe that our research has the potential to expand disaster education.

Computer-aided surgery (CAS), the intraoperative application of biomedical visualization techniques, appears to be one of the most promising fields of application for augmented reality (AR), the display of additional computer-generated graphics over a real-world scene. Typically a device such as a head-mounted display (HMD) is used for AR. However, considerable technical problems connected with AR have limited the intraoperative application of HMDs up to now. One of the difficulties in using HMDs is the requirement for a common optical focal plane for both the realworld scene and the computer-generated image, and acceptance of the HMD by the user in a surgical environment. In order to increase the clinical acceptance of AR, we have adapted the Varioscope (Life Optics, Vienna), a miniature, cost-effective head-mounted operating binocular, for AR. In this paper, we present the basic design of the modified HMD, and the method and results of an extensive laboratory study for photogrammetric calibration of the Varioscope's computer displays to a real-world scene. In a series of 16 calibrations with varying zoom factors and object distances, mean calibration error was found to be 1.24 +/- 0.38 pixels or 0.12 +/- 0.05 mm for a 640 x 480 display. Maximum error accounted for 3.33 +/- 1.04 pixels or 0.33 +/- 0.12 mm. The location of a position measurement probe of an optical tracking system was transformed to the display with an error of less than 1 mm in the real world in 56% of all cases. For the remaining cases, error was below 2 mm. We conclude that the accuracy achieved in our experiments is sufficient for a wide range of CAS applications.

Medical simulations bridge theory and practice in immersive settings. During this unique form of education, learners experience challenging medical scenarios without risking patient harm. The effectiveness of simulations stem from their ability to induce autonomic stress responses, which potentiate memory formation. Educators have adopted virtual reality (VR) and augmented reality (AR) to supplement traditional, mannequin-based simulations. In this Pro-Con commentary article, we discuss the competitive advantages and limitations of VR and AR simulation for medical training. VR uses computer-generated images (CGI) within head-mounted displays (HMDs) to enhance learning. Gamification of medical procedures in VR improves acquisition of complex skills, positioning VR simulation as a pivotal training tool. Participant embodiment while in VR develops non-technical skills such as improved communication and enhanced empathy. The placement of participants within CGI worlds that would otherwise be difficult or impossible to recreate situate VR as the ideal next step in simulation evolution. VR is superior to AR given its lower hardware costs, expansive software libraries, and complete immersion in CGI compared to limited holographic fields of view within AR. By displaying holograms within the participant's natural world, AR is primed to replace screen and VR technologies as the premier learning adjunct. The integration of real-world instruments with AR holograms provides innumerable methods for teaching procedural skills. In addition, AR enhances pre- and intra-operative planning by overlaying holographic, radiographic patient images over their own bodies. Because AR has the unique feature of maintaining direct eye contact between participants, scenarios that improve communication skills are easily created with holograms in the real world, eliminating the need for an entirely CGI VR environment. Immersive simulation efforts should skip the costs of creating VR scenarios and redirect efforts to developing AR simulation software. Although both VR and AR have limitations related to cost and ergonomics, immersive technologies are relatively more affordable and versatile than traditional mannequins and physical simulation centers. As adjuncts to enhance traditional simulation curricula, we advocate for continued research to demonstrate the validity and utility of these immersive technologies.

Two main concepts of Head Mounted Displays (HMD) for augmented reality (AR) visualization exist, the optical and video-see through type. Several research groups have pursued both approaches for utilizing HMDs for computer aided surgery. While the hardware requirements for a video see through HMD to achieve acceptable time delay and frame rate seem to be enormous the clinical acceptance of such a device is doubtful from a practical point of view. Starting from previous work in displaying additional computer-generated graphics in operating microscopes, we have adapted a miniature head mounted operating microscope for AR by integrating two very small computer displays. To calibrate the projection parameters of this so called Varioscope AR we have used Tsai's Algorithm for camera calibration. Connection to a surgical navigation system was performed by defining an open interface to the control unit of the Varioscope AR. The control unit consists of a standard PC with a dual head graphics adapter to render and display the desired augmentation of the scene. We connected this control unit to a computer aided surgery (CAS) system by the TCP/IP interface. In this paper we present the control unit for the HMD and its software design. We tested two different optical tracking systems, the Flashpoint (Image Guided Technologies, Boulder, CO), which provided about 10 frames per second, and the Polaris (Northern Digital, Ontario, Canada) which provided at least 30 frames per second, both with a time delay of one frame.

1 IntroductionNowadays, the institutes already use in the process of the advantages of mobile technology, such as portability (the students have easy access at any time to information), the use of digital assets (audio and video files) and huge amount of textual information. This study proposes a new system approach for improving the process by Mobile Augmented Reality. The features of this technology stimulate the environment and consider that the student's motivation is the most important factor in learning.The existing literature [1] highlights two different approaches for augmented reality (AR). Firstly, the authors consider that AR is a system which has the following characteristics: Combines real and virtual; Interactive in real time; Registered in 3-D. Secondly [1] considers Augmented Reality part of Virtual Continuum. This context is composed of two elements: Real Environment - which contains all representations from real life and Virtual Environment - which combines different elements from virtual life. ARs are considered closer to reality than virtual environment because this type of systems are supposed to extend the real objects with virtual elements.According to [2] Augmented Reality is a technology that extends the real world elements with 2D or 3D computer generated objects and lets the users interact with them. Also, the authors present three types of devices which can be used to view the result of AR technology: a Head Mounted Display (HMD), a mobile device - with at least one back camera and a desktop or a laptop computer.Similarly, [2] considers mobile technology as an alternative teaching resource because the users have easy access in real time to information. Also, mobile devices in the process two main problems of traditional are solved: the location and time. Likewise, [1] considers that mobile is a type of eLearning without restrictions of time and space and this technology improves the quality of classical environments, but does not replace them.Other researches, such as [3] and [4] highlight the benefits of a Mobile Augmented Reality system based on tracking objects. In [3] is proposed a mobile augmented reality system based on visual recognition. According to the authors the visual recognition consists into tracking objects identified in real world with the camera of the mobile device and augmenting the scene with virtual objects created by MAR technology. Similarly, [4] presents a Mobile Augmented Reality system bases on 3D registration technology. According to the authors the 3D registration represents the tracking of the position and pose of the mobile device in the real time and real life and finally use these information to insert in the real world the virtual scene created by MAR. The 3D registration technology is based on two type of approaches: markers and natural features. Recently, the 3D registration for MAR uses GPS and sensors from mobile devices to provide different information about position and pose of the camera and combine them with computer vision to improve the speed and accuracy of the system.Other studies, such as [5] propose a makerbased Mobile Augmented Reality solution. The application is used by a Vocational Educational and Training (VET) program for supporting the maintenance process of a car. The authors define VET as education programs that are designed for learners to acquire the knowledge, skills and competencies specific to a particular occupation, trade or class of occupations or trades(p. 49-50). Moreover, in [5] is presented an AR application used by VET students for basic mathematics skills, which is based on videogames.More studies, such as [6] present a Mobile Augmented Reality solution for French language which is based on gamification didactic method. The author, Bernadette Perry, describes gamification as using gamebased mechanics, aesthetics and game thinking to engage people, motivate action, and promote learning (p. …

This chapter introduces design and principles of head mounted displays (HMDs), as well as their state-of-the-art examples, for augmented reality (AR). Section 2 introduces a brief history of head mounted displays, human vision system, and application examples of see-through HMDs. Section 3 describes designs and principles of HMDs, such as typical configurations of optics, typical display elements, and major categories of HMDs. Section 4 gives typical characteristics of HMDs, such as resolution, field of view, and distortion. Section 5 describes human perceptual and health issues such as depth perception and safety. Finally, Section 6 gives conclusions with future challenges and prospects. For researchers, learners and HMD developers, this chapter is a good start point to learn basics, state of the art technologies, and future research directions of HMDs. For system developers and end-users, this chapter will give a good insight to HMDs to choose a suitable HMD for their purposes.