Considerations on volumetric 3D display systems
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The requirements of display systems are governed by the manner in which the visual world is perceived. An overview of the human visual system, including a discussion of depth cues, is presented and this is followed by a review of 3D display techniques, which includes a comprehensive discussion of volumetric systems. Volumetric displays in which the display volume is swept out by the periodic motion of a 2D screen are termed swept-volume displays; one such system, known as the Cathode Ray Sphere (CRS), is discussed in detail. A number of swept-volume displays, including the CRS, employ a rotating target screen addressed by radiation beams from sources which are stationary with respect to the screen motion. Regions of the display volume which correspond to the beam impinging on the screen at very acute angles are difficult to address accurately and are termed dead zones. The form and position of these regions is determined for both planar and helical screen geometries, and the dependence on the position of the beam source is shown. One particular configuration, namely a planar screen addressed by an equatorial beam source, is examined in detail, and a comprehensive investigation of the factors contributing to the dead zone is presented. The extra dimension of the display space makes an exhaustive raster-type scan of the display volume difficult to achieve on displays in which the voxels are generated sequentially; only the visible voxels comprising the image are thus depicted. Two procedures to order the voxels for display on swept-volume displays such as the CRS are introduced, and the dependence of their optimum performance on the values of certain system parameters is determined. The performance of the two methods is compared on the basis of the voxel positioning error in the direction of screen motion. Volumetric displays which do not employ a moving component to create the volume are termed static volume displays; one means of generating voxels in such a volume is to employ a two-step excitation of fluorescence process. The rate equations governing a simple model system encapsulating this mechanism are determined and solved numerically to indicate the relative timing of the two pumping radiation pulses that maximises the brightness of the resultant voxel. The nonuniformities and anisotropies in certain image quality parameters, such as voxel density, which arise in the display volume are discussed for a range of volumetric techniques, both swept and static volume. A filtering operation included in the graphics pipeline is proposed as a means of ensuring the display volume provides a uniform voxel density. A number of images, image sequences and simple application programs, created to evaluate the visualisation capabilities of the CRS, are discussed.