How Virtual Reality Technology Functions

If you recall the virtual reality (VR) craze of the early 1990s, you likely envision specific pieces of VR equipment. During that time, items like headsets and motion-sensitive gloves were featured in magazines, sold as toys, and appeared in films, all of which presented a futuristic, high-tech, yet bulky look.

More than ten years have passed since the original VR media frenzy. While many technologies have rapidly advanced, much of the hardware used in virtual reality today remains largely unchanged.

Despite initial appearances, the field of virtual reality continues to evolve, though at a slower pace compared to other technological domains. Progress often stems from other sectors such as military or entertainment. Venture capitalists tend to overlook virtual reality unless there are direct applications linking the research to other industries.

What equipment is essential for VR? Depending on how you define VR, it could be as simple as a computer with a monitor, keyboard, or mouse. However, most VR researchers agree that a true virtual environment provides users with a sense of immersion. Since a regular computer screen can easily break this immersion, most VR setups incorporate more sophisticated display systems. Other basic input devices like a keyboard, mouse, joystick, or controller wand are typically included in VR systems.

This article will explore the different types of VR equipment, discussing their pros and cons. We'll begin with head-mounted displays.

Head-mounted Displays

A Head-mounted Display (HMD) is exactly as it sounds: a display device you wear on your head. Typically, HMDs are mounted inside a helmet or goggles. These displays are designed so that no matter where the user looks, the screen remains in front of their eyes. Most HMDs feature one screen for each eye, creating the illusion of depth in the images.

Most HMD monitors are typically Liquid Crystal Displays (LCD), although you may encounter older versions that use Cathode Ray Tube (CRT) displays. LCD monitors are smaller, lighter, more energy-efficient, and cheaper than CRT models. However, CRTs do have advantages such as superior screen resolution and brightness. The downside is that CRT displays tend to be bulky and heavy, making them uncomfortable to wear, often requiring a suspension system to counterbalance the weight. These suspension mechanisms, though, can limit the user's movement, affecting their immersion experience.

Some HMD models do use alternative display technologies, though these are quite rare. These other display technologies include:

There are several reasons why these display technologies are not commonly used in HMDs. Many of these options have limited resolution and brightness. Some can only display monochromatic images. Others, such as VRD and plasma technologies, might be effective in an HMD but are prohibitively expensive.

Many head-mounted displays are equipped with built-in speakers or headphones to deliver both visual and audio output. Almost all advanced HMDs are connected to the VR system’s CPU via cables, as wireless systems lack the speed needed to prevent latency issues. Additionally, HMDs almost always feature a tracking device that adjusts the on-screen perspective based on the user's head movements. (We’ll explore tracking devices in a future section.)

Certain systems incorporate a unique pair of glasses or goggles along with additional display hardware. In the following section, we’ll explore one such system—the CAVE display.

Virtual Reality and the CAVE

The CAVE system, developed by students and researchers at the University of Illinois - Chicago, is widely regarded as the most immersive VR display system for virtual environments. CAVE stands for Cave Automatic Virtual Environment.

A CAVE is a compact room or cubicle where at least three walls (and sometimes the ceiling and floor) function as massive displays. This setup offers users a broader field of view than most head-mounted displays can provide. Users can also freely move within a CAVE system without being tethered to a computer, though they are required to wear specialized goggles similar to 3-D glasses.

The active walls are actually rear-projection screens. A computer generates the images displayed on each screen, forming a unified virtual environment. The images are presented in a stereoscopic format, alternating rapidly. The lenses in the goggles have shutters that open and close in sync with these alternating images, creating a perception of depth for the user.

Tracking devices attached to the goggles communicate with the computer to adjust the projected images as the user moves through the environment. Users typically carry a controller wand to interact with virtual objects or navigate the environment. Multiple users can be present in a CAVE simultaneously, though only the person wearing the tracking device will control the point of view, while others will act as passive viewers.

In the next section, we will explore another type of virtual reality display, known as the workbench.

Virtual Reality Workbenches

One display technology that some VR experts consider only loosely connected to virtual environments is the workbench display. In the early '90s, Larry Rosenbaum, the Computer Science Liaison Scientist at the Office of Naval Research, led a team of Navy engineers in developing a large display that multiple users could view together. The display can be seen either vertically or tilted horizontally like a table or workbench.

Users wear special goggles while interacting with the workbench, similar to a CAVE system. Each user observes the same image projected by the workbench. Due to stereoscopic projection and the goggles' lens shutters, the displayed objects seem to possess a three-dimensional quality.

The reason some VR researchers believe the workbench isn't a true virtual environment is due to its lack of immersion. Since the display doesn't occupy the user's entire field of vision, they remain aware of being in the real world, even though virtual objects can be manipulated. There's no virtual world to explore—if the user looks away from the screen, they will simply see a physical room. Nonetheless, workbench displays still offer great utility.

One application of the workbench display is for medical training. A surgeon can rehearse a procedure on a virtual, three-dimensional patient while being surrounded by a real medical team. If the same task were performed using an HMD, the individuals nearby would either be computer-generated characters or avatars representing other people. With the workbench display, interaction with actual people feels natural and entirely authentic.

Workbench displays are also beneficial for military tacticians. Programmers can design realistic, three-dimensional models of battlefields, giving military personnel an accurate view of combat situations. A well-designed model can also uncover potential bottlenecks or hidden enemy positions.

Other uses of workbench displays include visualizing scientific research or product research and development.

In the upcoming section, we will examine various devices that enable users to engage with virtual environments.

Virtual Reality Clothing

While producing high-quality graphics and display systems remains a vital aspect of virtual reality, many experts believe that developing intuitive user interaction devices is even more important. Common devices like keyboards or joysticks are simple to use, but they often detract from the immersive experience. Ideally, the user would not even be aware of the interaction device during use.

Although progress has been slow, there have been some fascinating advancements in human-machine interfaces (HMI). While various industries contribute to the development of graphics technologies, few are as invested in exploring new forms of HMI. The primary industries pushing HMI forward include entertainment, academic institutions, and small VR companies. Nevertheless, there are some intriguing HMI devices already in use in certain VR systems, especially wearable devices such as gloves and bodysuits.

From the very outset, gloves have been central to the VR revolution, even if they weren't originally designed for virtual reality applications. By wearing a wired glove, users can manipulate virtual objects through hand gestures. While many refer to these gloves as DataGloves or Power Gloves, these names actually apply to specific glove models, not the general category. Despite variations in design, all gloves share the same aim: providing users with an intuitive way to control digital data.

Certain gloves track finger movement using fiber-optic cables. Light travels from an emitter to a sensor through the cables, and the amount of light reaching the sensor changes depending on the user's hand position. For instance, when a user makes a fist, less light reaches the sensor, which sends the data to the VR system's CPU. These gloves generally need to be calibrated for each individual user to ensure proper functionality. The official DataGlove is an example of a fiber-optic glove.

Some gloves are made with strips of flexible material coated in electrically conductive ink to detect finger movements. As the fingers bend or straighten, the resistance along the strips shifts. The CPU processes these changes in resistance and reacts accordingly. While these gloves aren't as precise as fiber-optic models, they are typically more affordable.

For superior accuracy and responsiveness, a dexterous hand master (DHM) is the best option. The DHM uses sensors attached to each finger joint, which are connected to mechanical links, essentially creating an exoskeleton. These gloves offer better precision than fiber-optic or electrically conductive models, though they tend to be bulkier and less flexible.

Next, we'll explore VR input devices.

Virtual Reality Input Devices

If you can't afford a CAVE system or a DataSuit, don't worry—there are still some alternatives to help users navigate virtual environments without relying on a wand or joystick. Researchers believe that devices promoting more natural movement in a VR space enhance the user's sense of immersion. With this goal in mind, engineers and scientists have developed several user navigation systems.

One option for navigation in VR is the treadmill. This system allows users to remain stationary in the real world, while experiencing the sensation of walking through a virtual environment. Researchers have found it easy to connect a treadmill to a computer, so that the user's steps cause the system's graphics to adjust accordingly. However, traditional treadmills have the limitation of movement in only two directions: forward or backward.

Some companies have advanced the technology by creating omni-directional treadmills. These devices give users the ability to move in any direction. Unlike traditional treadmills, which rely on a single motor to provide either forward or backward motion, omni-directional treadmills use two motors. From the user's perspective, this allows movement in any direction—forward, backward, left, or right. The treadmill's surface is made of a network of belts and cables that allow the user to walk in any direction they choose.

An alternative to a treadmill is the pressure mat, commonly seen in games like 'Dance Dance Revolution.' The most common type of pressure sensor used in these mats is the electromechanical sensor, which acts as a relay that activates when pressure is applied. When pressure is exerted, the circuit closes and an electrical current flows, signaling the system to adjust the graphics output accordingly.

VirtuSphere, Inc. offers a unique device for navigating virtual environments. Resembling a giant hamster ball, the VirtuSphere allows users to walk inside a spherical structure. The sphere rests on a stable platform equipped with wheels that roll in all directions, keeping the sphere in place while enabling movement. Sensors in the wheels track the user's direction, and the virtual view inside the user's HMD updates based on this movement.

In some CAVE systems, VR researchers are experimenting with a technique called passive haptics. While 'haptics' generally refers to systems that provide physical feedback to users, passive haptics differs in that it does not actively push against the user. Instead, it uses real-world objects to represent virtual elements in a VR environment. For example, a real folding table may act as a virtual kitchen counter. These tangible objects improve immersion by providing users with something real to touch while navigating the simulation.

Next, we will explore the various types of tracking systems found in HMDs, DataGloves, and other virtual reality equipment.

Virtual Reality Tracking Systems

Tracking devices are crucial components in any virtual reality setup. They communicate with the system's processing unit to relay the orientation of the user's viewpoint. In VR systems that allow users to move within a physical space, these trackers detect the user's location, the direction they are moving in, and their speed.

There are several types of tracking systems used in VR, but they all share some common features. These systems can detect six degrees of freedom (6-DOF), which include the position of the object in three-dimensional space (x, y, z coordinates) and its orientation. Orientation consists of three components: yaw, pitch, and roll.

When you wear an HMD, the view adjusts based on your head movements. This means the image changes as you look up, down, left, or right, and also when you tilt your head or move it forward or backward while keeping your gaze steady. The trackers on the HMD monitor where you're looking, and then the CPU sends the appropriate images to the screens inside the HMD.

Every tracking system consists of a signal generator, a sensor that detects the signal, and a control unit that processes the signal and communicates with the CPU. Some systems require you to attach the sensor to the user or the user's equipment, with the signal emitters placed at fixed points in the environment. In other systems, the user wears the emitters while the surrounding environment is equipped with sensors.

The signals transmitted from emitters to sensors can be in different forms, such as electromagnetic, acoustic, optical, or mechanical signals. Each technology has its own advantages and drawbacks.