Perhaps we can split this into two questions.
Firstly, what is data visualisation? This is the activity of presenting data (from whatever source, in whatever field of study) into some sort of visual format that enhances - or even allows- one's ability to interpret those data. This can range from a simple two-dimensional graph, to a fully immersive, virtual-reality-based environment involving advanced soiftware, multiple projectors, haptics devices and real-time computational steering. In short, presenting data in such a way that allows us to use our eyes, and the brain's associated visual processing, to look for patterns and relationships in data.
Second, what is visualisation, in a more general context? This is a wider and less defined concept. It is, perhaps, the development or presentation of some idea or concept in a visual form. This can range from a presentation of an architectural design via a sketch or, more commonly these days, as a three-dimensional image; to computer-generated imagery that is used in the film industry. The source (i.e. that which is to be visualised) does not need to be data (which we most often think of as being numerical data); it is just something which needs to be, or is better expressed or presented, in a visual form.
More and more, visualisation is being achieved through software. This is especially the case for data visualistion, where many specific software applications have been written explicitly for the purpose of visualising numerical data (examples include AVS Express, Open DX, Visualisation Toolkit, and many more).
Humans have stereoscopic vision. We have two laterally-displaced eyes, and the slight differences between the left-eye and right-eye images are processed by the brain to furnish us with a sense of depth perception.
This is the natural way in which we view the world, and we intuitively use that direct depth perception as an aid to our interpretation of the world. By definition, it requires the brain to be provided with two separate images- two views of the same scene, differing due to the different locations of the imaging systems (our eyes). Most artificial scenes- be they drawings, paintings, photographs, TV screens, computer monitors- present the eyes with a single image only. Although we view that "scene object" with both eyes, there is no sterescopic imformation within that scene object. It is "flat", since both eyes see essentially an identical image of that scene object, and there is no information therein for the direct perception of depth (although other clues, such as object occlusion and lighting effects in that artificial scene are interpreted so as to provide some depth information).
Thus, in the viewing of these monoscopic artificial scenes, we are missing out on a rich source of visual information that we take for granted when viewing the natural world. What we're concerned with here is the attempt to introduce natural depth perception (stereopsis) into such artificial scenes- to imbue such scenes with a greater amount of the visual richness that we use as a matter of course in our day-to-day view of the world.
To achieve this, we must first acquire or generate the image pairs that are required. This may involve capturing real world content (i.e. photography or filming of real world scenes) or computer-generated or other artificial content- or, indeed, the combination of these.
We will look at such acquisition in the next FAQ item.
We will consider the following two broad categories :
Real world content
By this is meant the use of still photography or video/film techniques to capture natural scenes (including studio techniques such as filming elements against green/blue screen). One technique is to use a single camera that is moved horizontally between shots- this can be used when the scene to be captured is static. A more generally usable scenario is to use a pair of identical cameras, mounted in such a way to ensure that their optical axes are horizontally separated by an amount that is appropriate for the distance from the cameras to the target object.
In this context, each camera will acquire the visual content to be presented to the viewer's corresponding eye during later stereoscopic display and viewing.
The camera pair will record the left and right images simultaneously. The level of synchnronism may not be perfect, but it should be sufficient that there is no time-based difference between the two left/right images large enough to spoil the stereo effect when the images are viewed together. How the cameras are mounted depends on a number of factors, including the camera body size and shape, how close the cameras' optical axes need to be, is there a need for rapid variation of interaxial separation, etc. Mounting methods range from simple mounting bars using fixed holes, to motorised mirror-based rigs that allow arbitrary axial separation with a large variety of camera bodies.
Imaginary / non-real content
By this is meant the development, by computer-generated imagery or other techniques, of images that are not directly derived from imaging real world scenes. This could be the result of employing ray-tracing software such as POV-Ray, 3DS, Maya and a host of others; or even by carefully planned and executed drawing or painting. In a CGI example, one might render an image pair for a virtual scene, with different virtual camera locations in each scene; the virtual cameras for the virtual scene are then analogues of a real-world camera pair.
In this context, separate renders of a scene are used to generate the visual content to be presented to the viewer's corresponding eye during later stereoscopic display and viewing.
No matter how the content is obtained, the image pairs must somehow be presented in an appropriate way to the viewer. This will be discussed briefly in the next FAQ entry.
Once one has obtained some stereoscopic (a.k.a. "3D") content, how is it to be displayed? This is indeed a rapidly evolving area, with strong interest in devleoping hardware for the consumer market. Large-scale uptake is some way off yet... we will discuss some of the basic principles, as well as some hardware which is currently in use.
The basic requirement is that each of the viewer's eyes must receive the image that is intended for it- and only that image. The most common way to achieve this is via the use of glasses which somehow allow or block the left or right image as required. That is, the right eye must see oinly the image intended for the right eye; and similarly for the left eye. It is the job of the "3D glasses" to make this happen.
There are several methods for achieveing this, some of which we'll now look at briefly.
Colour separation
Anaglyph The viewer's glasses have different colour filters for each eye, a common example being red and cyan. The left and right images are processed so that their colour content matches the range of colours admitted by the corresponding eye filter. Typically, these red/cyan images can be composited into a single image, so that an anaglyph image can be presented as a single image that's encoded with the stereo information.
Infitec A refinement of the anaglyph method, this projection method uses matched filters for the projectors and viewer's glasses. Each left or right filter covers segments of the entire visual range of colours; the transmission curve resembles a comb filter, rather than the broad block or pass of traditional anaglyph filters. Two projectors are required.
Polarised
Two projectors are used, each with a polarising filter (usually in front of the lens). The planes of polarisation of the filters are crossed. The viewer's glasses have matching filters, and thus each eye sees only the matching projector's image.
Shutter glasses
A single projector (or monitor) alternately displays the left and right images. The viewer wears glasses which contain LCD panels which are alternately opaque and clear (that is, when the left panel is opaque, the right is clear, and vice versa). The glasses operate in synchronism with the projector; when the left image is displayed, the left eye panel is clear and the right opaque, and vice versa. This is done at a rate sufficiently rapid that most people do not perceive any flickering in the image.
Glasses-free displays
Currently suited only to much smaller numbers of viewers than any of the above methods, it is possible to produce monitor displays which simultaneuosly display both the left and right images, yet ensure that each of the viewer's (or viewers') eyes see only the correct image without the use of glasses.
Yes indeed. At present, we have three sets of imaging hardware.
If you would like to make use of any of these, please contact us.
eRSA offers two visualisation suites.
The Vislab has a single 4m x 3m screen, and employs the Infitec system. Movable desks seat five comfortably, and up to around twenty may be accomodated with chairs.
The South Australian Virtual Reality Centre (SAVRC) has three 2.3m x 1.3m screens, for an overall screen of 6.9m x 1.3m (with blending between screens 1 and 2). Shutter glasses are used to enable stereo viewing. Tiered seating accomodates 23, and the room can be opened up to allow up to 100 people to use the space.
Non-visualisation use of the suites has included filming and photography locations, due to the ability to back-project images and control lighting very closely, and also as a green-screen facility.
There is a Linux PC in the Vislab which is used to run the AVS Express data visualisation package, and has 3D glasses for stereo viewing of its monitor.
eRSA also two haptics devices - see here for more information, and contact us to check on their availability.
Vislab
SAVRC