KEYWORDS: 3D displays, Visualization, 3D image processing, Electronics, 3D volumetric displays, Projection systems, Digital micromirror devices, OpenGL, 3D applications, Software frameworks
We present a software and hardware foundation to enable the rapid adoption of 3-D displays. Different 3-D displays - such as multiplanar, multiview, and electroholographic displays - naturally require different rendering methods. The adoption of these displays in the marketplace will be accelerated by a common software framework. The authors designed the SpatialGL API, a new rendering framework that unifies these display methods under one interface. SpatialGL enables complementary visualization assets to coexist through a uniform infrastructure. Also, SpatialGL supports legacy interfaces such as the OpenGL API. The authors’ first implementation of SpatialGL uses multiview and multislice rendering algorithms to exploit the performance of modern graphics processing units (GPUs) to enable real-time visualization of 3-D graphics from medical imaging, oil & gas exploration, and homeland security. At the time of writing, SpatialGL runs on COTS workstations (both Windows and Linux) and on Actuality’s high-performance embedded computational engine that couples an NVIDIA GeForce 6800 Ultra GPU, an AMD Athlon 64 processor, and a proprietary, high-speed, programmable volumetric frame buffer that interfaces to a 1024 x 768 x 3 digital projector. Progress is illustrated using an off-the-shelf multiview display, Actuality’s multiplanar Perspecta Spatial 3D System, and an experimental multiview display. The experimental display is a quasi-holographic view-sequential system that generates aerial imagery measuring 30 mm x 25 mm x 25 mm, providing 198 horizontal views.
A 360-degree-viewable volumetric 3-D display has been developed by Actuality Systems, Inc. It has a resolution of 768 x 768 x 198, has a 24 Hz refresh rate, contains an embedded graphics processing system, and uses dithering methods to create images of 3-bit to 21-bit color. The 3-D display system is a visualization platform, comprised of a combination of hardware and software designed for ease-of-integration into existing visualization systems. The system design is briefly recounted. Key enhancements are described, such as the development of a volumetric visualization software platform. Examples are given which guide the system engineer who needs to include a volumetric display into a visualization solution.
KEYWORDS: 3D displays, Visualization, 3D volumetric displays, 3D image processing, Raster graphics, Projection systems, OpenGL, Digital signal processing, Electronics
An 8-color multiplanar volumetric display is being developed by Actuality Systems, Inc. It will be capable of utilizing an image volume greater than 90 million voxels, which we believe is the greatest utilizable voxel set of any volumetric display constructed to date. The display is designed to be used for molecular visualization, mechanical CAD, e-commerce, entertainment, and medical imaging. As such, it contains a new graphics processing architecture, novel high-performance line- drawing algorithms, and an API similar to a current standard. Three-dimensional imagery is created by projecting a series of 2-D bitmaps ('image slices') onto a diffuse screen that rotates at 600 rpm. Persistence of vision fuses the slices into a volume-filling 3-D image. A modified three-panel Texas Instruments projector provides slices at approximately 4 kHz, resulting in 8-color 3-D imagery comprised of roughly 200 radially-disposed slices which are updated at 20 Hz. Each slice has a resolution of 768 by 768 pixels, subtending 10 inches. An unusual off-axis projection scheme incorporating tilted rotating optics is used to maintain good focus across the projection screen. The display electronics includes a custom rasterization architecture which converts the user's 3- D geometry data into image slices, as well as 6 Gbits of DDR SDRAM graphics memory.
Interferant spectral features that are stable in both time and optical frequency oftentimes can be made negligible with respect to spectral features of interest by simple data processing techniques such as absorbance subtraction. With varying degrees of success more sophisticated processing of these same spectra can reject these interferant spectral features even when not stable in time. Beyond this, a classic approach to rejecting spectral interferants is to operate at higher and higher spectral resolutions so that ultimately the interferant feature separates from the feature of interest so that it is of negligible effect as an interferant. For a given observation time this approach results in a loss of radiometric sensitivity. A further reduction in radiometric sensitivity may occur since the maximum allowed etendue in a fixed parameter system must also be decreased to accommodate the higher resolution. (This reduction in etendue is more likely in the instance of a process control application as opposed to an open path monitoring application). The use of offset scanning and field widening as techniques for regaining this lost sensitivity are discussed.
Over the past two decades major advances in FTS have allowed process control engineers to more readily consider the use of this measurement technique. The most striking advance has been in the area of data processing facilitated by extraordinary increases in computing power. The development of improved optical fibers has provided a means for bringing the measurement to the factory floor while providing a remote `laboratory environment' site for the less-than-robust spectrometer optical systems. Recent advances in auto-aligned systems again permit consideration of moving the spectrometer system to locations in close proximity to the process itself. Generally, these systems are based on the use of HeNe lasers for the reference and auto-align mechanism. This results in large and expensive measurement heads to again argue against placement of the spectrometers proximate to the process. This paper describes the successful use of a solid state light source in place of the HeNe laser in an auto- aligned and referenced FTS system which allows consideration of small and inexpensive process control spectrometers. A review of a spectrometer system utilizing a combination of auto-align and referencing technologies utilizing diode sources is presented. DOD and NASA support enabled this dual-use technology to be developed.
Dynamic alignment has been demonstrated as a practical approach to alignment maintenance for systems in the infrared region of the spectrum. On the basis of work done by OPTRA, this technique was introduced in commercial Fourier transform spectrometer systems in 1982 and in various forms is now available from a number of manufacturers. This paper reports on work by OPTRA to extend the basic technique to systems operating in the ultraviolet. In addition, this paper reports the preliminary results of the development of an alignment system using a laser diode in place of a gas laser normally found in dynamic alignment systems. A unique optical system and spatial heterodyne technique allows for achievement of a metrology system with characteristics that fully satisfy the requirements of an ultraviolet spectrometer system.
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