The Sky's The Limit
Linda Law
Issue: Volume 35 Issue 7: (Dec 2012)

The Sky's The Limit

Planetariums, until recent years, were environments exclusively designed to create visualizations of the space beyond our planet. The core technology of these places relied on projecting pinpoints of light onto a reflective surface in a completely blacked-out dome. For a long time, technological developments were focused mainly on the machines that created these representations, beginning with the Carl Zeiss Company and followed by a handful of other firms around the world.

These star projectors, which are still in some dome environments, were later enhanced by content from arrays of computer-controlled slide projectors. Also, the addition of lasers with scanning devices made it possible to create dazzling light shows set to music, thereby expanding audiences for planetariums as this non-educational entertainment became possible.

The Sinra Dome at the Science Museum in Tokyo, which opened in 2009, offers stereo projection using six stereo pairs of projectors, giving audiences an immersive view of the heavens.

With the development of 3D animation in computer graphics, increasing computing power, and video projection systems of increasingly higher resolution, a new type of visualization system emerged for planetariums. Beginning with Evans & Sutherland in the early 1980s, the first digital projectors showed vector graphics of star fields and line art. Later, systems were capable of projecting fully digital data generated from 3D animation programs. These early systems suffered from lack of resolution and didn’t really compare to the star projections produced by the older technology, but they could project animations created in the computer, and thus various planetariums began to develop new kinds of content.

Domes are typically hemispherical and can be orientated level, as was the case in most early planetariums (requiring circular rows of seats that allow the viewer to lean back in order to experience the full view), or tilted forward to varying degrees (typically five to 30 degrees from the horizontal position in order to facilitate easier viewing using stadium seating). These various configurations afford different types of experiences and have significance, as you will see, when we look at 3D projection in domes.

Digital Evolution

Projection systems are constantly evolving. For mono and stereo domes alike, increases in resolution and brightness, accompanied by lower costs, have resulted in changes nearly every year. Smaller, non-stereo domes—and larger domes with the newer, more powerful projectors—can be served by a single projector equipped with a specially designed fish-eye lens, which sits in the center of the dome. With this design, from optical engineer D’nardo Collucci, the framework was formed for the innovative work of his and partner David McConville’s company, The Elumenati. This company has pioneered the use of single projectors in small domes, making these systems portable and easy to set up.

At the other end of the scale, large domes (70 feet in diameter or bigger) in locales such as the Hayden Planetarium at the Rose Center for Earth and Space in New York City (installed by Global Immersion) have systems with multiple projectors served by banks of computers to create the projected content. These installations require a very high level of precision in installation and maintenance in order to obtain the illusion of one seamless image. With these, 3D content generated in the computer is processed to correct for the curvature of the dome, and then is further rendered out as separate views for each of the projectors, with edge blending to make a seamless hemisphere. The projectors have to be precision-matched, and the bulbs have to be maintained to equal brightness and color temperature—an art in itself.

A look from inside the domed interactive virtual reality theater, installed by Global Immersion, at the Hellenic Cosmos exhibition center of the Foundation of the Hellenic World in Athens.

These existing systems create a deep, immersive experience that feels like 3D, although it really isn’t. Full-dome video exploits a number of visual cues that send data to our brain in ways that help it to create 3D inside our head. 3D perception is the result of multiple visual clues that build the 3D image. Recent research indicates that we have two main forms of vision: the region that is in sharp focus and which we see through the central part of our eyes, and the peripheral vision that surrounds that. We tend to think that our sharply focused central region is the most important, but that may not be true in terms of how we perceive 3D. Full-dome projection, even in 2D, provides a wide field of data to the peripheral vision of the viewer, and this is a key element in creating a convincing sense of immersion.

Other visual clues include movement, occlusion, perception, depth of field, color, and contrast. In scenes that are moving, the foreground travels faster than the imagery in the distance, and the brain uses this information to compute depth. With digitally navigated journeys through star fields, this can create an especially convincing sense of depth. In situations where parts of objects are obscured by other objects, each eye sees different amounts that are occluded, thereby creating visual information that the brain translates into 3D. And all of us have experienced perspective, whereby a car traveling down a road moving away from you will appear smaller as it moves farther away, and the road narrower.

Artists and filmmakers alike, fully aware of depth of field, know that objects in the foreground are more clearly defined than those in the distance. But many may not know that color also has an effect: Blue hues tend to recede, and red hues tend to pop. Meanwhile, deep black in the screen helps to create a sense of depth, so this aspect has been a contributing factor to the improvement of full-dome video, as the most recent projection systems are more effectively achieving better blacks and higher contrast.

Imiloa Planetarium in Hilo, Hawaii, projects stereoscopic full-dome images, which are created using four cinema-quality Sony SXRD 4k digital projectors.

A well-planned, full-dome experience can really draw a person in quite convincingly, except that it will always have only the illusion of depth going backward on the screen because of the depth cues described earlier.

The Stereo Component

So, if we can get a fairly convincing sense of 3D from a system with a single view, why do we want to experience a fully stereo view in a dome?

Up until the turn of this century, the older star projectors mainly showed content of outer space in domes. We were always looking outward to the screen; we didn’t expect space to project toward us into the dome. The new projection systems are enabling us to visualize a much wider range of data: We can look at things on a macro level or on a human scale, and here is where stereo 3D really shines. This technology can produce images that can project many feet out into the volume of the dome. You have the sense that you can almost touch the imagery, and it can appear to be passing through the screen. The screen itself effectively disappears.

Domes have another advantage over flat screens in regard to stereo projection. With a flat screen, careful attention must be paid to creating content that fits within the rectangle of the projection screen. If the content projecting out in front of the screen spills over the edges of the frame, the illusion is broken and the image appears to flatten out. With the dome format in stereo, there is no rectangular frame to be broken; the plane of the screen disappears, and there is much more freedom to create imaginatively.

Content for stereo 3D movies for flat screens is typically produced by either creating a 3D model in the computer and rendering it out through two virtual cameras placed at the optimum interocular distance (the distance between the centers of each of our eyes) or by recording footage with two high-resolution video cameras. Stereo 3D today is being seen on the latest cinema systems (a large percentage are using the RealD solution) by viewers wearing glasses that will only transmit light that is circularly polarized in a particular direction—each eye is circularly polarized in opposite directions.

The Imiloa Planetarium, which opened in 2006, houses the world’s first 3D stereoscopic, digital, full-dome planetarium system with a resolution of 4096x4096, or roughly four times that of HDTV.

The RealD system uses only one projector that outputs at a very high frame rate. It alternates projecting the content stream for each eye, but because the frame rate is so high, viewers are unaware of the flickering. The electro-optical device in front of the projection lens has the effect of creating the opposite polarization for each stream of images prepared for the two eyes, and the glasses effectively make sure that each eye will see only one image.

To retain the polarization of the light, the RealD systems use a special projection screen that maintains the polarization when the light is reflected from it and only minimally absorbs or scatters light, thus keeping the image bright. The interocular distance is maintained evenly over the whole screen, as the surface is flat. This works effectively on a flat screen in a cinema, but not so well in a dome.

It is also difficult—although not impossible—to retrofit an appropriate reflective surface that will retain polarization to an existing dome, and any seams in the surface of the dome can seriously damage the stereoscopic effect. However, 3D can be achieved in other ways. The old technique, known as anaglyph (which uses red and blue or green lenses, one on each eye to separate two images that have been produced in those colors), can be used but is unsatisfactory in that, at best, it produces only a black-and-white image.

The La Géode domed theater with stereo projection in Paris contains a 1,000-square-meter screen with a multi-channel Barco Galaxy passive stereo display.

Infitec has produced an updated version of this technology that uses lenses with narrow-band filters, which essentially divide the spectrum into six bands-—three pairs of bands that are close to one another on the spectrum. Each eye has a different filter that allows light to pass through from the bands, so although each eye is receiving light from a different region of the spectrum, when seen with both eyes, the brain perceives the full spectrum, thereby producing an accurately colored image. So, if you take a stereo pair of images and code them with these filters, you can achieve very high quality stereo without compromising color. These glasses have the advantage of not requiring a special screen, and they are reusable, as they can be cleaned.

A third system of projection—one that uses shuttered glasses—is available for showing stereo. These glasses are made from small liquid crystal displays that can be made to synchronize with alternate frames of the film showing from a single projector via a wireless emitter. The digital film is prepared so that the stereo pairs alternate in sequence on the film, and the film rate is doubled in order to remove flickering effects. The system produces high-quality stereo, but the glasses are expensive, more fragile, and not so easy to clean.

Choosing an Approach

These approaches are being explored by various dome facilities around the world. It is apparent, though, that each system has its own advantages and disadvantages, and the individual requirements of the particular theater ends up defining which system is ultimately used.

3D projection systems can also vary widely in how many projectors are used and in what type of configuration. They can vary from two to as many as 12 edge-blended projectors, and the resolution can be as high as 8k x 8k. These high resolutions are now coming close to matching the spectacular images of IMAX film. It should also be noted that IMAX was the first to venture into the realm of 3D in domes, and although this is not a direction the company has continued to expand, there is still at least one IMAX dome theater in operation today.

There is also an inherent issue that all 3D dome theaters have to address: With the conventional mode of projecting 3D in a dome, the system has to be optimized to achieve the best effect. In a forward-tilting dome, the two views required for stereo (regardless of how many projectors are being used and edge-blended) are best viewed in a sweet spot that is at the front and center of the screen. As you move out of this sweet spot, on both the left and right sides, you progressively lose the 3D effect and, if you turn your head to face the back, the image is inverted.

There are several tricks being employed to minimize this effect of losing 3D, which include raking the seating in the theater to maximize chairs in the optimal regions and masking off the projected side areas. Designing the content for placement in these areas of the screen is part of the content creation process and falls to the artists. This approach, however, does rule out seeing 3D projected accurately over the whole surface of the dome and is, therefore, not practical for hemispherical domes that are level (not tilted).

Some existing full-dome theaters are also expanding their capabilities by installing secondary systems that can project stereo onto sections of the dome—a 3D window, if you will. This partial approach allows them to show existing 3D footage that has been created for flat screens and, when blended with the 2D content on the rest of the dome, expands their capabilities. There is some distortion of the imagery, but this seems to be acceptable.

However, another technology is emerging that promises to address the issue of achieving stereo over the whole surface of the dome. It is developed by a company named Micoy, and the firm claims to be the world’s only provider of this patented and unique proprietary 360-degree 3D omni-directional format. Although Don Pierce, president of Micoy, wouldn’t discuss the actual optics of the system, he notes that it uses a collection map that is based on true-world optics.

“In our first step, there is an acquisition phase, where we are collecting all the data by our image sensor, and that’s basically recorded onto a CCD (charge-coupled device). Then our second phase is to go on and remap all those pixels into their proper order, which then, in turn, allows us to create two stereo pairs,” Pierce explains. “In terms of computer graphics, it works the same way. We are actually raytracing the pixels onto the CCD, and then we are extrapolating them back out and remapping them.”

This system was first devised for collecting data via an array of 84 cameras, but the initial design proved cumbersome. Further development has produced a system that works brilliantly for computer graphics, and this is now available as a plug-in for both Autodesk’s Maya and 3ds Max. A high-resolution camera system is still in development, but the high level of interest the company has generated is promising to speed up the research that is currently under way. In fact, a major manufacturer of dome systems, Evans & Sutherland, has licensed the Micoy technology and is incorporating it into the company’s line of domes.

This new approach offers exciting possibilities, as it can be applied to other types of immersive systems as well, including CAVES, cylindrical screens, and curved walls. It also can be used for 3D game applications on small, inflatable domes that completely immerse players.

Various Venues

Looking at the big picture, 3D in domes offers a uniquely immersive medium that fits the growing needs of our technological world. Many small 3D systems are being used privately by medical institutions, corporations, and military facilities around the world for a wide range of visualization applications. 3D domes are also being incorporated into adventure rides, some of which were developed by Synthespian Studios and can be experienced on The Amazing Adventures of Spider-Man ride at Universal Studios in Orlando, Florida, and Osaka, Japan.

Planetariums are beginning to embrace the technology both from a standpoint of visualizing their astronomical data and as an immersive environment for education—and as an extraordinary new form of entertainment. A recently formed international professional organization, Imersa, is a great resource for anyone wishing to plug into the wide array of activities in this field.

Although there are a number of new facilities being funded worldwide and equipped with state-of-the-art hardware and software housed in often beautifully designed buildings, there is a blind spot that seems to apply to them all. They are not developing serious budgets for content development. It appears that it is easier to get funds for equipment and facilities than it is for creating content. This is very shortsighted, as these facilities are only as good as the content they show.

This is a brand-new medium that is wide open for creative exploration. Its potential is staggering. In many ways, it is the first stage of the dream many hold from the forward-thinking of Star Trek—the holodeck. To exploit this potential, there needs to be serious funding for the creative content and access for artists and facilities where experimental work can be explored.

The expansive growth of 3D in the film industry is spilling over into many areas. We are seeing a surge of interest in 3D gaming, digital holography, 3D for TV, and 3D for a range of visualization and medical applications. The development in dome technology reflects this trend, but it also moves us forward into the realm of immersive 3D, something that has been largely explored in the domains of industrial and university research. 3D in domes offers a range of creative possibilities that go beyond the experience of 3D cinema and, in many ways, represents the cutting edge of cinematic media.

Linda Law ( is a digital/3D artist who has been working in holography since 1975.