Cyclorama: the oft-neglected Tool
The word cyclorama comes from the joining of two Greek terms: Cycl, which means to circle; Orama, which means to view. Put them together and you have a circling view.
The cyclorama was the 19th century's version of TV, video game, and virtual reality, all (literally) rolled into one. By painting a large, highly detailed and realistic scene on the inside of a massive cylinder, they gave viewers standing in the middle, the feeling of really being a part of that scene.
Cylinders worked better than cubes, as they have no natural corners - every part of the image, viewed straight on, feels just as real as the last, and there is no distorting of perception, no shadowing even suggesting corners. A participant, who searches for such, will find such an effort proves completely fruitless. The mind is drawn into the cyclorama, and it feels <I>real</I>.
The origin of Cycloramas
The first concept of the cyclorama in recorded history, was when it was patented by an Irish painter named Robert Barker. Apparently, the invention occurred to him when Baker was out climbing a hill in the city of Edinburgh, Scotland. When he reached the top and saw the city spread out around and below him, he decided he desired to capture the view. He opened his first cyclorama in Edinburgh in 1787.
A cyclorama would seem natural to use in VR, for the background, or skybox. Additionally, for virtual tours, or other QuickTime use.
VR worlds in the current level of computing technology, and for the foreseeable future, cannot cre4eate whole worlds, massive planets with full weather systems and backdrops stretching for hundreds of miles with any degree or realism. Most home PCs struggle with a quarter mile of highly rendered scenery.
To compensate for these problems, VR environments often employ skyboxes. Traditionally, these are simple cubes with up to 6 different textures placed on the faces. By careful alignment, a viewer in the exact middle of the skybox will perceive the illusion of a real 3-D world around it, made up of those 6 faces.
As a viewer moves through a 3-D scene, it is common for the skybox to remain stationary with respect to the viewer. This technique gives the skybox the illusion of being very far away since other objects in the scene appear to move, while the skybox does not. This imitates real life, where distant objects such as clouds, stars and even mountains appear to be stationary when the viewpoint is displaces by relatively small distances. Effectively, everything in a skybox will always appear to be infinitely distant from the viewer. This consequence of skyboxes dictates that designers should be careful not to carelessly include images of discrete objects in the textures of a skybox since the viewer may be able to perceive the inconsistencies of those objects' sizes as the scene is traversed.
The source of a skybox can be any form of texture including photographs, hand-drawn images, or pre-rendered 3-D geometry. Usually, these textures are created and aligned in 6 directions, with viewing angles of 90 degrees, (which covers up the 6 faces of the cube).
However, with all such skyboxes, if you look closely, or are careful as you turn, it is relatively easy to make out the corners of the box. This is especially true if the skybox is animating, with a moving sun, or, most dramatically, with a fireworks display. When explosions of colour are going off in the skybox, it is distractingly easy to identify the corners - they literally leap out at you.
Use of a cyclorama for the skybox, improves the situation. Instead of several square sections, it is composed of one long rectangular one. The only challenge then, is to ensure the two ends fit together seamlessly.
Beyond the cyclorama
The cyclorama itself is not without flaws. Fundamentally, its very tubular nature lets it down. A cyclorama is perfect if you just look straight ahead or slightly up or slightly down. If, however, you look right the way up, you see the perspective start to skew, as the tube rises and rises, towards a distant convergence point, high in the sky.
To counter this stretching, stringing out effect, it becomes necessary to adapt the cyclorama, and limit its reach. The curved walls are still perfect for displaying, but they only work so far. The reach has to be capped off, but without resorting to corners.
Enter the sky dome.
The skydome or hemisphere display. Defined as half of a sphere bounded by a great circle, a hemisphere fits perfectly onto a cyclorama, and creates a natural sky feeling, preserving the corner less feeling. Hemispherical displays are used in many high-end VR facilities for their realistic, seamless visuals - an advancement of the cycloramas. Unlike a cyclorama, however, a hemisphere cannot just wrap a normal image round a tube.
Often, physical hemispheres resort to overlapping projectors covering the surface area, each projector system responsible for just a portion of the image. In software, such as when used for skydomes, the image is similarly broken up into sections, and each twisted and deformed before drawn onto part of the dome. This adds significant processing overhead to creating a skybox, or interactive cyclorama, however, the resulting effect of perfect believability, is usually worth it all.