Yonggang Ha

A compact optical see-through head-worn display with occlusion support

We are proposing an optical see-through head-worn display that is capable of mutual occlusions. Mutual occlusion is an attribute of an augmented reality display where real objects can occlude virtual objects and virtual objects can occlude real objects. For a user to achieve the perception of indifference between the real and the virtual images superimposed on the real environment, mutual occlusion is a strongly desired attribute for certain applications. This paper presents a breakthrough in display hardware from a mobility (i.e. compactness), resolution, and a switching speed based criteria. Specifically, we focus on the research that is related to virtual objects being able to occlude real objects. The core of the system is a spatial light modulator (SLM) and polarization-based optics which allow us to block or pass certain parts of a scene which is viewed through the head-worn display. An objective lens images the scene onto the SLM and the modulated image is mapped back to the original scene via an eyepiece. We are combining computer generated imagery with the modulated version of the scene to form the final image a user would see.

Development of head-mounted projection displays for distributed, collaborative, augmented reality applications

Distributed systems technologies supporting 3D visualization and social collaboration will be increasing in frequency and type over time. An emerging type of head-mounted display referred to as the head-mounted projection display (HMPD) was recently developed that only requires ultralight optics (i.e., less than 8 g per eye) that enables immersive multiuser, mobile augmented reality 3D visualization, as well as remote 3D collaborations. In this paper a review of the development of lightweight HMPD technology is provided, together with insight into what makes this technology timely and so unique. Two novel emerging HMPD-based technologies are then described: a teleportal HMPD (T-HMPD) enabling face-to-face communication and visualization of shared 3D virtual objects, and a mobile HMPD (M-HMPD) designed for outdoor wearable visualization and communication. Finally, the use of HMPD in medical visualization and training, as well as in infospaces, two applications developed in the ODA and MIND labs respectively, are discussed.

Enabling a continuum of virtual environment experiences

We define a virtual environment as a set of surroundings that appear to a user through computer-generated sensory stimuli. The level of immersion-or sense of being in another world-that a user experiences within a VE relates to how much stimuli the computer delivers to the user. Thus, one can classify VEs along a virtuality continuum, which ranges from the real world to an entirely computer-generated environment. We present a technology that allows seamless transitions between levels of immersion in VEs. Milgram and Kishino (1994) first proposed the concept of a virtuality continuum in the context of visual displays. The concept of a virtuality continuum extends to multimodal VEs, which combine multiple sensory stimuli, including 3D sound and haptic capability, leading to a multidimensional virtuality continuum. Emerging applications will benefit from multiple levels of immersion, requiring innovative multimodal technologies and the ability to traverse the multidimensional virtuality continuum.

A mobile head-worn projection display.

A recent advancement was achieved in the integration and miniaturization of a binocular head-worn projection display (HWPD) conceived for fully mobile users. The devised display, referred to as Mobile HWPD (M-HWPD), offers see-through capability through custom-designed, light-weight projection optics and an integrated commercial-off-the-shelf (COTS) retro-reflective screen to display full color stereoscopic rendered images augmenting the real world. Moreover, the light-weight optical device (i.e., approximately 8g per eye) has the ability to project clear images at three different locations within near- or far-field observation depths without loss of image quality. In this paper, we first demonstrate the miniaturization of the optics, the optical performance, and the integration of these components with the retro-reflective screen to produce an M-HWPD prototype. We then show results that demonstrate the feasibility of superimposing computer-generated images on a real outdoor scene with the M-HWPD.

Optical assessment of head-mounted displays in visual space.

The optics of head-mounted displays (HMDs) is designed from the pupil of the eye to the miniature display, and the optics is thus commonly solely assessed in the plane of the miniature display. Such assessment does not provide information that usefully interfaces with task-based performance metrics. We present a comprehensive framework for the assessment of the optics of HMDs in visual space, which applies to nonrotationally symmetric systems as well. Four key measures of visual performance are presented, and macro files were implemented to validate the framework. We illustrate the methods using an Erfle eyepiece.

Design of a wearable wide-angle projection color display

In this paper, we investigate the design and fabrication of ultra-light weight projection lenses for color wearable displays. Driven by field of view requirements from 40 degree to 90 degrees, we employed the combination of plastic, glass, and diffractive optics to yield less than 10g optics per eye. The approach centers on the use of projection optics instead of eyepiece optics to yield most compact and high image quality designs. The implementation of the fabricated 52 degrees lens in a teleportal head-mounted display and remote collaborative environment is demonstrated. We also present the design results for a 70 degrees design.

Teleportal Augmented Reality System: Integrating Virtual Objects, Remote Collaborators, and Physical Reality for Distributed Networked Manufacturing

Components and potential manufacturing applications of the teleportal augmented reality (AR) system are described. This teleportal system is designed to support applications such as distributed 3D design and work-team collaboration. The optomechanical design of an emerging type of AR head-mounted display (HMD), referred to as the Teleportal Head-Mounted Projection Display (T-HMPD) is detailed. A feature of HMPDs is the invariance of the optics size and weight across a significant increase in field of view (FOV). Results are shown for 52° and 70° FOVs projection optics. Research on associated technologies and methods that provide the basis for an integrated distributed manufacturing AR system is introduced, which includes calibration and registration of virtual and physical objects, the creation of AR tool spaces around the body of a mobile user, a face-to-face collaboration tool, and finally an integration of the teleportal AR technologies within the Artificial Reality Centre (ARC) Work Room.

Projection-based head-mounted displays for wearable computers

The projection based head-mounted display (HMD) constitutes a new paradigm in the field of wearable computers. Expanding on our previous projection based HMD, we developed a wearable computer consisting of a pair of miniature projection lenses combined with a beam splitter and miniature displays. Such wearable computer utilizes a novel conceptual design encompassing the integration of phase conjugate material (PCM) packaged inside the HMD. Some of the applications benefiting from this innovative wearable HMD are for government agencies and consumers requiring mobility with a large field-of-view (FOV), and an ultra-light weight headset. The key contribution of this paper is the compact design and mechanical assembly of the mobile HMD.

Albertian errors in head-mounted displays: I. Choice of eye-point location for a near- or far-field task visualization.

A theoretical investigation of rendered depth and angular errors, or Albertian errors, linked to natural eye movements in binocular head-mounted displays (HMDs) is presented for three possible eye-point locations: the center of the entrance pupil, the nodal point, and the center of rotation of the eye. A numerical quantification was conducted for both the pupil and the center of rotation of the eye under the assumption that the user will operate solely in either the near field under an associated instrumentation setting or the far field under a different setting. Under these conditions, the eyes are taken to gaze in the plane of the stereoscopic images. Across conditions, results show that the center of the entrance pupil minimizes rendered angular errors, while the center of rotation minimizes rendered position errors. Significantly, this investigation quantifies that under proper setting of the HMD and correct choice of the eye points, rendered depth and angular errors can be brought to be either negligible or within specification of even the most stringent applications in performance of tasks in either the near field or the far field.

Embedded Training Display Technology for the Army's Future Combat Vehicles

Abstract : This paper describes an innovative solution for a low cost, compact, lightweight (i.e. <500g), see-through, deployable head-mounted projection display (HMPD) system for embedded training simulation of out-the window (OTW) scenes for Future Combat System ground vehicles. A unique capability is that virtual images are visible only when the user is looking at strategically located screens that simulate windows in the real environment. The display is inherently see-through with the physical surroundings visible through the display optics. This provides users with unencumbered access to the vehicles controls while viewing the simulated OTW scene. In this paper we shall detail the underlying principle of the display, its optical design and assessment, and show an early integration of the optics in a HMPD prototype for demonstration.