Through a human-subject experiment, we investigated the effects of focal distance on depth perception and accommodative response in an optical see-through augmented reality (AR) display. The display was able to provide focus cues and was rigorously calibrated. The near-field distances ranging between 3 diopters and 1 diopter were considered as target distance. In the experiment, it was found that the perceived depth of a virtual object was significantly biased along with the focal distance of virtual image plane of the display. In addition, the experimental results implied that the perceived depth of a virtual object would be potentially more accurate in the condition where the focal distance of virtual image plane was consistent with the target distance than in the conditions where it could deviate from the target distance. Regarding accommodative response, it was found that the response to a virtual object changed along with the focal distance of virtual image plane as well as the target distance. However, the changing rate depending on target distance was less steep in the conditions where the focal distance could be mismatched with the target distance than in the condition where it was consistent with the target distance. In the consistent condition, the changing rate of accommodative responses to virtual objects were similar to that for their physical counterparts.

State-of-the-art optical see-through head-mounted displays (OST-HMD) for augmented reality applications lack the ability to correctly render light blocking behavior between digital and physical objects, known as mutual occlusion capability. In this article, we present a novel optical architecture for enabling a high performance, occlusion-capable optical see-through head-mounted display (OCOST-HMD). The design utilizes a single-layer, double-pass architecture, creating a compact OCOST-HMD that is capable of rendering per-pixel mutual occlusion, correctly pupil-matched viewing perspective between virtual and real scenes, and a wide see-through field of view (FOV). Based on this architecture, we present a design embodiment and a compact prototype implementation. The prototype demonstrates a virtual display with an FOV of 34° by 22°, an angular resolution of 1.06 arc minutes per pixel, and an average image contrast greater than 40 percent at the Nyquist frequency of 53 cycles/mm. Furthermore, the device achieves a see-through FOV of 90° by 50°, within which about 40° diagonally is occlusion-enabled, and has an angular resolution of 1.0 arc minutes (comparable to a 20/20 vision) and a dynamic range greater than 100:1. We conclude the paper with a quantitative comparison of the key optical performance such as modulation transfer function, image contrast, and color rendering accuracy of our OCOST-HMD system with and without occlusion enabled for various lighting environments.

Augmented reality (AR) has been widely used that combines human with the digital world tightly at an unprecedented level, and various types of optical see-through head-mounted displays (OSTHMDs) have been actively developed to meet the requirement of everyday AR use. Correct mutual occlusion between real and virtual objects is often necessary for displaying realistic virtual images for users in the AR application scenarios. Some optical designs have been proposed to realize mutual occlusion by means of an OSTHMD in recent years. However, all of them support a limited field of view (FOV) that is much narrower than that of a natural human. The main limiting factor of the FOV of general OSTHMDs is the limited numerical aperture (NA) of the lenses. To address the problem, we propose an OSTHMD based on the double ellipsoidal mirror structure to avoid a stack of lenses and to achieve a wide FOV close to that of the naked eye with small distortion. A pair of imaging lenses are carefully arranged, then assembled between the two ellipsoidal mirrors with a pinhole mask to improve image quality. An experiment using a monocular prototype shows that a sharp see through view is achieved which remains clear regardless of the focus of the eye-simulating camera. An image undistortion algorithm is also developed to obtain a full-view display, enabling a virtual image to be displayed spanning a super wide FOV of H160°×V74°. Finally, per-pixel mutual occlusion of a wide FOV of H122°×V74° is realized by placing a spatial light modulator (SLM) in front of the entrance pupil.

Depth sensor is an essential element in virtual and augmented reality devices to digitalize users' environment in real time. The current popular technologies include the stereo, structured light, and Time-of-Flight (ToF). The stereo and structured light method require a baseline separation between multiple sensors for depth sensing, and both suffer from a limited measurement range. The ToF depth sensors have the largest depth range but the lowest depth map resolution. To overcome these problems, we propose a co-axial depth map sensor which is potentially more compact and cost-effective than conventional structured light depth cameras. Meanwhile, it can extend the depth range while maintaining a high depth map resolution. Also, it provides a high-resolution 2D image along with the 3D depth map. This depth sensor is constructed with a projection path and an imaging path. Those two paths are combined by a beamsplitter for a co-axial design. In the projection path, a cylindrical lens is inserted to add extra power in one direction which creates an astigmatic pattern. For depth measurement, the astigmatic pattern is projected onto the test scene, and then the depth information can be calculated from the contrast change of the reflected pattern image in two orthogonal directions. To extend the depth measurement range, we use an electronically focus tunable lens at the system stop and tune the power to implement an extended depth range without compromising depth resolution. In the depth measurement simulation, we project a resolution target onto a white screen which is moving along the optical axis and then tune the focus tunable lens power for three depth measurement subranges, namely, near, middle and far. In each sub-range, as the test screen moves away from the depth sensor, the horizontal contrast keeps increasing while the vertical contrast keeps decreasing in the reflected image. Therefore, the depth information can be obtained by computing the contrast ratio between features in orthogonal directions. The proposed depth map sensor could implement depth measurement for an extended depth range with a co-axial design.

Developing head-mounted displays (HMDs) that offer uncompromised optical pathways to both digital and physical worlds without encumbrance and discomfort confronts many grand challenges, both from technological perspectives and human factors. Among the many challenges, minimizing visual discomfort is one of the key obstacles. One of the key contributing factors to visual discomfort is the lack of the ability to render proper focus cues in HMDs to stimulate natural eye accommodation responses, which leads to the wellknown problem of vergence-accommodation conflict. This paper provides a comprehensive summary of various technical approaches toward enabling focus cues in HMDs for both virtual reality (VR) and augmented reality (AR) applications.

The ray-shift phenomenon means the apparent distance shift in the display image plane between virtual and physical objects. It is caused by the difference in the refraction of virtual display and see-through optical paths derived from optical combiners that are necessary to provide a see-through capability in optical see-through head-mounted displays. In this work, through a human-subject experiment, we investigated the effects of ray-shift phenomenon induced by the optical combiner on depth perception for near-field distances (40 cm-100 cm). In our experiment, we considered three different configurations of optical combiner: horizontal-tilt and vertical-tilt configurations (using plate beamsplitters horizontally and vertically tilted by 45°, respectively), and non-tilt configuration (using rectangular solid waveguides). Participants' depth perception errors in these configurations were compared with those in an ordinary condition (i.e., the condition where physical objects are directly shown without the displays) and theoretically estimated ones. According to the experimental results, the measured percentage depth perception errors were similar to the theoretically estimated ones, where the amount of estimated percentage depth errors was greater than 0.3%. Furthermore, the participants showed significantly larger depth perception errors in the horizontal-tilt configuration than in an ordinary condition, while no large errors were found in the vertical-tilt configuration. In the non-tilt configuration, the results were dependent on the thickness of optical combiner and target distance.

Many error sources have been explored in regards to the depth perception problem in augmented reality environments using optical see-through head-mounted displays (OST-HMDs). Nonetheless, two error sources are commonly neglected: the ray-shift phenomenon and the change in interpupillary distance (IPD). The first source of error arises from the difference in refraction for virtual and see-through optical paths caused by an optical combiner, which is required of OST-HMDs. The second occurs from the change in the viewer's IPD due to eye convergence. In this paper, we analyze the effects of these two error sources on near-field depth perception and propose methods to compensate for these two types of errors. Furthermore, we investigate their effectiveness through an experiment comparing the conditions with and without our error compensation methods applied. In our experiment, participants estimated the egocentric depth of a virtual and a physical object located at seven different near-field distances (40∼200 cm) using a perceptual matching task. Although the experimental results showed different patterns depending on the target distance, the results demonstrated that the near-field depth perception error can be effectively reduced to a very small level (at most 1 percent error) by compensating for the two mentioned error sources.

One of the problems in using head-mounted displays (HMDs) is that the virtual images shown through the HMDs are usually distorted due to their optical distortions. In order to correctly compensate the optical distortions through a pre distortion technique, accurate values of the distortion parameters are required. Although several distortion calibration methods have been developed in prior work, these methods suffer a few critical limitations. In this paper, we proposed a method for robustly estimating the optical distortion parameters of both immersive and (optical) see-through HMDs, without the limitations of existing methods. The proposed method is based on photogrammetry and considers not only the radial distortion but also the tangential distortion. Its effectiveness was evaluated through an experiment conducted with two different types of HMDs, an optical see-through head-mounted projection display and a commercially available non-see-through HMD. According to the experimental results, the proposed method showed significantly lower reprojection error than a previous method proposed by Owen et al. In addition, when both the radial and tangential distortions were considered, the proposed method was significantly more effective than when only the radial distortion was considered.

Most state-of-the-art optical see-through head-mounted display (OST-HMD) lacks mutual occlusion capability between computer-rendered and real objects so that the virtual view through an OST-HMD appears “ghost-like”, floating in the real world. In this paper, we demonstrated a light-weight, compact OST-HMD with mutual occlusion capability by exploring a highly innovative optical approach based on emerging freeform optical design and fabrication technologies. Our approach enabled us to achieve an occlusion-capable OST-HMD system with a very compelling form factor and high optical performance. The proposed display technology is designed for highly efficient liquid crystal on silicon (LCoS) type spatial light modulator (SLM) and bright Organic LED (OLED) microdisplay, which is capable of working in both indoor and outdoor environments. Our current design offered a 1280×1024 color resolution with a field of view (FOV) of 40 degrees and lightweight optics about 30 grams per eye.

We investigate the effects of viewing conditions and rotation methods on different types of collaborative tasks in a two-user colocated tabletop augmented reality (AR) environment. The viewing condition means how the manipulation of a tabletop world by one user is shown in the other users' views and the rotation method means what type of input devices is used to rotate the tabletop world for alternative orientations. Our experiment considered two viewing conditions (consistent view and inconsistent view), two rotation methods (direct turn and indirect turn), and two task types (synchronous and referring-strong type, and asynchronous and orientation-strong type). A 3D display environment called "Stereoscopic Collaboration in Augmented and Projective Environments (SCAPE)" was utilized as a test environment. According to the results, the viewing conditions had significant effects on several objective and subjective measurements. On task completion time, their effect for the synchronous and referring-strong type of task was opposite to that for the asynchronous and orientation-strong type of task. On the other hand, the rotation methods had significant effects only on the accumulated turn angle (for both task types) and the number of negotiation phrases (only in the inconsistent viewing condition for the asynchronous and orientation-strong type of task).

The processor and cooling subsystems of high-performance servers consume a significant portion of total system power. In this paper, we use the server energy-efficiency benchmark SPECpower_ssj2008 to assess dynamic power management strategies for these sub-systems on an IBM POWER 750 platform.

The perceived depth accuracy is a fundamental performance metrics for an augmented reality display system. Many factors may affect the perceived depth of a head-mounted display (HMD), such as display resolution, interpupillary distance (IPD), conflicting depth cues, stereoacuity, and head tracking error. Besides these typical limiting factors to an HMD-type system, the perceived depth through a head-mounted projection display (HMPD) may be further affected by the usage of a retroreflective screen. In this paper, we will evaluate the perceived depth accuracy of an HMPD system using a perceptual depth matching method. The main factor to be investigated in our study is the position of a retroreflective screen relative to the projection image plane, with the projection image plane placed at different distances to the user. Overall, it is found that the ratio of the judged distance to real distance and the standard deviation of the judged distance increase linearly with the reference object distance. A transition effect from depth underestimation to overestimation has been observed at the reference object distance of around 1.4m. The position of a retroreflective screen only has a significant effect on the depth judgment error around this switching point. The paper also analyzes various effects brought by a retroreflective screen on the depth judgment. The depth cue and the image luminance reduction brought by a retroreflective screen could be the main factors that affect the depth judgment accuracy.

In this paper, we quantify the effects of two physical affordances on user interaction in an augmented virtual environment: the grounding of datasets on a workbench and the augmentation of a Magic Lens interface tool. We investigated the effects of these affordances on subjects' performance and behavior in an information gathering task. Our results indicated that grounding had a significant main effect and that there was significant interaction between grounding and interface factors. Specifically, subjects tended to perform better with some level of affordance than none at all, although performance with grounded datasets decreased in the presence of augmented Magic Lens. Further, both affordance factors influenced behavior by reducing head mobility.

In this paper, we investigate the effects of viewing conditions and rotation methods on different types of collaborative tasks in a tabletop AR environment in which two users are co-located. The viewing condition means how the manipulation of a tabletop world by one user is shown in the other users' view and the rotation method means what type of input devices is used to rotate the tabletop world for alternative orientations. Our experiment considered two different viewing conditions-consistent view and inconsistent view and two different rotation methods-direct turn and indirect turn. In the experiment, a 3D display environment called ¿Stereoscopic Collaboration in Augmented and Projective Environments (SCAPE)¿ was utilized as a test environment, and two tasks were considered: Lego-like block building task and text label selection task. The former was designed for synchronous and referring-strong type, and the latter was designed for asynchronous and orientation-strong type. As dependent variables, various objective and subjective measurements including task completion time, quality of task result, turn angle, and questionnaire were measured. According to the results, the viewing conditions had significant effects on several objective and subjective measurements. On task completion time, their effect for the synchronous task was opposite to that for the asynchronous task. On the other hand, the rotation methods had significant effects only on turn angle.

We present the design and implementation of an optical see-through head-mounted display (HMD) with addressable focus cues utilizing a liquid lens. We implemented a monocular bench prototype capable of addressing the focal distance of the display from infinity to as close as 8 diopters. Two operation modes of the system were demonstrated: a vari-focal plane mode in which the accommodation cue is addressable, and a time-multiplexed multi-focal plane mode in which both the accommodation and retinal blur cues can be rendered. We further performed experiments to assess the depth perception and eye accommodative response of the system operated in a vari-focal plane mode. Both subjective and objective measurements suggest that the perceived depths and accommodative responses of the user match with the rendered depths of the virtual display with addressable accommodation cues, approximating the real-world 3-D viewing condition.

Spatially variant resolution method has been widely explored for Gaze Contingent Displays (GCDs). Recently several studies suggested that spatial chromatic foveation can further improve the sampling efficiency and save computational resources and communication bandwidths in GCDs. In this paper, we explore the spatial variance of the contrast sensitivity function (CSF) of the human visual system (HVS) to examine the potential of spatialchromatic foveation in GCDs. The proposed algorithm reveals that, not only the spatial resolution, but also the chrominance complexity can be monotonically degraded from the center of the field of view (FOV) to the periphery of a GCD. A perceptually-based spatialchromatic foveation metric is derived. Applying the proposed hue-resolution foveation metric, we demonstrate that over 65% of bandwidth can be saved.

Most existing stereoscopic head mounted displays (HMDs), presenting a pair of stereoscopic images at a fixed focal distance, lack the ability to correctly render the naturally coupled accommodation and convergence cues. Psychophysical studies have shown that such displays may cause many adverse consequences such as visual fatigue, diplopic vision, degraded oculomotor response, and depth perception errors. In this paper, we present a see-through HMD with addressable focal planes utilizing a novel active optical element - a liquid lens. The element, with a varying optical power from -5 to 20 diopters, is able to address the focal distance of the HMD from infinity to the near point of the eye. A monocular prototype was built from off-the-shelf elements and experimental results are presented to validate the proposed designs. We also describe both subjective and objective measurements of the accommodation responses of the viewer to the focal distances presented by the prototype.

In the paper, we describe an optical system which is capable of providing external access to both the sensor and the lens aperture (i.e., projection center) of a conventional camera. The proposed optical system is attached in front of the camera, and is the equivalent of adding externally accessible intermediate image plane and projection center. The system offers controls of the response of each pixel which could be used to realize many added imaging functions, such as high dynamic range imaging, image modulation, and optical computation. The ability to access the optical center could enable a wide variety of applications by simply allowing manipulation of the geometric properties of the optical center. For instance, panoramic imaging can be implemented by rotating a planar mirror about the camera axis; and small base-line stereo can be implemented by shifting the camera center. We have implemented a bench setup to demonstrate some of these functions. The experimental results are included.

Wide field of view (FOV) and high-resolution image acquisition is highly desirable in many vision-based applications. Several systems have reported the use of reflections off mirror pyramids to capture high-resolution, single-viewpoint, and wide-FOV images. Using a dual mirror pyramid (DMP) panoramic camera as an example, in this paper, we examine how the pyramid geometry, and the selection and placement of imager clusters can be optimized to maximize the overall panoramic FOV, sensor utilization efficiency, and image uniformity. The analysis can be generalized and applied to other pyramid-based designs.

In augmented reality (AR) applications, accurately registering a virtual object with its real counterpart is a challenging problem. The size, depth, and geometry, as well as the physical attributes of the virtual object, have to be rendered precisely relative to a physical reference. This paper presents a systematic calibration process to address the registration challenge in a custom-designed AR system, which is based upon recent head-mounted projective display (HMPD) technology. Following a concise review of the HMPD concept and our system configuration, we first present a computational model of the HMPD viewing system and requirements for the system calibration. Then, we describe, in detail, the calibration procedures to obtain estimates of unknown transformations, summarize the application of the estimates in a customized graphics rendering toolkit, and discuss the evaluation experiments and observations. Finally, the implementation of a testbed to demonstrate a successful registration is briefly described, and experimental results are presented

Magic Lens is a small inset window embedded in a large context display, which provides an alternative view to the region of interest selected from the context view. This metaphor is used for 3D visualization in our Augmented Virtual Environment infrastructure, SCAPE (Stereoscopic Collaboration in Augmented and Projective Environments), which is composed of an immersive room display for a high level of detail, life-size virtual world and a workbench display for simplified god-like view to the world. A tangible Magic Lens is used on the workbench display to allow direct and intuitive selection of continuous levels of detail, bridging the gap between the two extreme levels of detail in SCAPE. This paper presents our first step to the user evaluations of tangible Magic Lens. We conducted two sets of user evaluations, one mainly testing the lens aspect ratio, and another for the lens size. For both of the tests, two types of tasks are conducted: information gathering and relating the detailed information with the context. We found that the aspect ratio of a lens plays more important role in user preference for smaller lenses than for larger ones. Meanwhile, the size of a lens is the most important factor that affects the user performance in the two types of tasks.

The lack of image brightness is a common problem in optical see-through head-mounted displays (OST-HMD) where a beamsplitter is required to combine views from HMD image source and the direct-view of a real world scene. This problem is further aggregated in a head-mounted projective display (HMPD) due to the fact that light passes through the beamsplitter multiple times. We present a novel design of an ultra-bright polarized head-mounted projective display (p-HMPD). The image brightness observed by a viewer theoretically is four-times brighter than existing designs. We further demonstrate a design with currently available technology that leads to a display in which the observed image is significantly brighter than existing designs. Finally, experimental results from a bench setup are presented.

A mirror pyramid consists of a set of planar mirror faces arranged around an axis of symmetry and inclined to form a pyramid. By strategically positioning a number of conventional cameras around a mirror pyramid, the viewpoints of the cameras' mirror images can be located at a single point within the pyramid and their optical axes pointed in different directions to effectively form a virtual camera with a panoramic field of view. Mirror pyramid-based panoramic cameras have a number of attractive properties, including single-viewpoint imaging, high resolution, and video rate capture. It is also possible to place multiple viewpoints within a single mirror pyramid, yielding compact designs for simultaneous multiview panoramic video rate imaging. Nalwa [4] first described some of the basic ideas behind mirror pyramid cameras. In this paper, we analyze the general class of multiview panoramic cameras, provide a method for designing these cameras, and present experimental results using a prototype we have developed to validate single-pyramid multiview designs. We first give a description of mirror pyramid cameras, including the imaging geometry, and investigate the relationship between the placement of viewpoints within the pyramid and the cameras' field of view (FOV), using simulations to illustrate the concepts. A method for maximizing sensor utilization in a mirror pyramid-based multiview panoramic camera is also presented. Images acquired using the experimental prototype for two viewpoints are shown.

We have previously developed a collaborative infrastructure called SCAPE - an acronym for Stereoscopic Collaboration in Augmented and Projective Environments - that integrates the traditionally separate paradigms of virtual and augmented reality. In this paper, we extend SCAPE by formalizing its underlying mathematical framework and detailing three augmented Widgets constructed via this framework: CoCylinder, Magnifier, and CoCube. These devices promote intuitive ways of selecting, examining, and sharing synthetic objects, and retrieving associated documentary text. Finally we present a testbed application to showcase SCAPE's capabilities for interaction in large, augmented virtual environments.

Augmented reality (AR) superimposes computer-generated virtual images on the real world to allow users exploring both virtual and real worlds simultaneously. For a successful augmented reality application, an accurate registration of a virtual object with its physical counterpart has to be achieved, which requires precise knowledge of the projection information of the viewing device. The paper proposes a fast and easy off-line calibration strategy based on well-established camera calibration methods. Our method does not need exhausting effort on the collection of world-to-image correspondence data. All the correspondence data are sampled with an image based method and they are able to achieve sub-pixel accuracy. The method is applicable for all AR systems based on optical see-through head-mounted display (HMD), though we took a head-mounted projective display (HMPD) as the example. We first review the calibration requirements for an augmented reality system and the existing calibration methods. Then a new view projection model for optical see through HMD is addressed in detail, and proposed calibration method and experimental result are presented. Finally, the evaluation experiments and error analysis are also included. The evaluation results show that our calibration method is fairly accurate and consistent.

This paper presents a multi-user collaborative infrastructure, SCAPE (an acronym for Stereoscopic Collaboration in Augmented and Projective Environments), which is based on recent advancement in head-mounted projective display (HMPD) technology. The SCAPE mainly consists of a 3'/spl times/5' interactive workbench and a 12'/spl times/12'/spl times/9' room-sized walk-through display environment, multiple head-tracked HMPDs, multi-modality interface devices, and a generic application-programming interface (API) designed to coordinate the components. The infrastructure provides a shared space in which multiple users can simultaneously interact with a 3D synthetic environment from their individual viewpoints. We detail the SCAPE implementation and include an application example that demonstrates major interface and cooperation features.

In augmented reality (AR) applications, registering a virtual object with its real counterpart accurately and comfortably is one of the basic and challenging issues in the sense that the size, depth, geometry, as well as physical attributes of the virtual objects have to be rendered precisely relative to a physical reference, which is well known as the calibration or registration problem. This paper presents a systematic calibration process to address static registration in a custom-designed augmented reality system, which is based upon the recent advancement of head-mounted projective display (HMPD) technology. Following a concise review of the HMPD concept and system configuration, we present in detail a computational model for system calibration, describe the calibration procedures to obtain estimations of the unknown transformations, and include the calibration results, evaluation experiments and results.

A head-mounted projective display (HMPD) consists of a pair of miniature projection lenses, beam splitters and displays mounted on the helmet and retro-reflective sheeting materials placed strategically in the environment. This has recently been proposed as an alternative to existing 3D visualization devices. In this paper, we first briefly review HMPD technology, including its featured capabilities and the recent development in both display implementations and applications. Then the implementation of a testbed for playing a "Go" game with a remote opponent in a 3D augmented environment is described. The testbed not only demonstrates the capabilities of virtual-real augmentation and registration, the natural occlusion of virtual objects by real ones, interaction with augmented environments and networking collaboration, but also embodies part of our long-term objective to develop a collaborative framework in 3D augmented environments. Through the testbed, major calibration issues, such as accommodation/convergence considerations and determination of viewing transformations, are studied and discussed in detail. Both calibration methods and results are included, which are applicable to other applications. Finally, experimental results of the testbed implementation are presented.

Wide field of view (FOV) and high resolution are two desirable properties in many vision-based applications such as tele-conferencing, surveillance, and robot navigation. In some applications, such as 3D reconstruction and rendering, it is also desired that all viewing directions share a single viewpoint, the entire FOV be imaged simultaneously, in real-time, and the depth of field be large. In this paper, we review such a panoramic camera proposed by Nalwa in 1996 that uses reflections off planar mirrors to achieve the first four of the aforementioned capabilities He uses a single mirror pyramid (SMP) and a number of cameras that point to the individual pyramid faces. Together the cameras yield a visual field having a width of 360 degrees and a height same as that of the individual cameras. We propose a double mirror-pyramid (DALP) design that still achieves a 360-degree FOV horizontally but doubles the vertical FOV. It retains the other three capabilities namely high resolution, a single apparent viewpoint across the entire FOV, and real-time panoramic capture. We specify the visual field mapping from the scene to the sensor realized by, the proposed camera. Finally, an implementation of the proposed DMP design is described and examples of preliminary panoramic images obtained are included.

In this paper we discuss how to use a one-dimensional classifier for solving high dimensional classification problems. We propose Spin Discriminant Analysis (SDA), which enables us to construct a family of new classifiers. We prove that SDA is equivalent to ridged Linear Discriminant Analysis (LDA) when two classes are Gaussians with common covariance matrices. Moreover, we prove that classification based on Parzen's window, is a special case of SDA. In addition to theoretical investigations, we conduct extensive empirical studies, implementing SDA using Support Vector Machines (SVMs) as its one-dimensional classifiers. This SVM-based SDA implementation is named SpinSVM. Our experiments show that SpinSVM outperforms traditional high dimensional classifiers like SVMs, Classification Using Spline (CUS), classification-based Parzen's window, and LDA on most standard and synthetic datasets we tested.

Head-mounted projective displays (HMPD) have been recently proposed as an alternative to conventional eyepiece-type head-mounted displays. HMPDs consist of a pair of miniature projection lenses and displays mounted on the helmet and retro-reflective sheeting materials placed strategically in the environment. Its novel concept and properties suggest solutions to part of the problems of state-of-the-art visualization devices and make it extremely suitable for multiple-user collaborative applications and wearable systems. A brief review of conventional visualization techniques is followed by an extensive discussion of HMPD technology, which includes a summary of its features and a comparison with conventional head-mounted displays (HMDs), projection-based displays, and HMPDs. An ultra-light and compact design (i.e. 8g) of a projection lens system using diffractive optical element (DOE) as well as plastic components for a HMPD is presented. Through the usage of fast prototyping technology, a compact stereoscopic head-mounted prototype with weight less than 700 grams was implemented, and optomechanical adjustments and ergonomic considerations are discussed. Finally, the motivated application in multiuser tele-collaboration is described.