Grids Of Lines Research Articles

THE RAYCASTING ENGINE AND RAY REPRESENTATIONS: A TECHNICAL SUMMARY

Solid modeling is computationally intensive. Thus far its use in industry has been limited mainly to simple parts and simple applications, and this is not likely to change much until 'massive' computing power can be made available at an affordable cost. The RayCasting Engine is one specialized source of 'massive' computing power for solid modeling, and it is but the simplest member of a potentially large family of 'classification computers'. The RayCasting Engine (RCE) is a highly parallel, custom-VLSI computer that classifies grids of parallel lines against solids represented in CSG. The sets of parallel 'in' segments that the RCE produces are called ray representations (ray-reps); they can be thought of as sampled boundary representations. Ray-reps are obviously useful for graphics and mass-property calculation. Less obviously, they are surprisingly versatile if one exploits special properties – for example, boolean combination of solids by interval operations on ray-reps – and the fact that ray-reps are cheap to compute. Overall, the combination of a 'new' representation scheme (ray-reps) and a fast custom processor (the RCE) is changing our approach to solid modeling. We are now seeking 'brute force' solutions to problems, and are finding that some previously intractable problems – for example, spatial sweeping and offsetting – are effectively computable and easy to program. This paper summarizes the genesis and principles of the RCE, some important properties of ray representations, and some exemplary applications of the (ray-rep, RCE) combination.

Testing a model of intonation in a tone language.

Schematic fundamental frequency curves of simple statements and questions are generated for Hausa, a two-tone language of Nigeria, using a modified version of an intonational model developed by Gårding and Bruce [Nordic Prosody II, edited by T. Fretheim (Tapir, Trondheim, 1981), pp. 33-39]. In this model, rules for intonation and tones are separated. Intonation is represented as sloping grids of (near) parallel lines, inside which tones are placed. The tones are associated with turning points of the fundamental frequency contour. Local rules may also modify the exact placement of a tone within the grid. The continuous fundamental frequency contour is modeled by concatenating the tonal points using polynomial equations. Thus the final pitch contour is modeled as an interaction between global and local factors. The slope of the intonational grid lines depends at least on sentence type (statement or question), sentence length, and tone pattern. The model is tested by reference to data from nine speakers of Kano Hausa.

Stress operated random access, high-speed magnetic memory

The memory consists of a checkerboard pattern of transducers. Each transducer is connected to two lines of electrical conductors which form two grids of parallel lines. The grids are placed perpendicular to each other. A magnetic block is placed on top of each transducer. A magnetic field is applied to the system of magnetic blocks. It is slightly smaller than the coercive field H(c). One transducer generates a stress wave which will travel into the magnetic block adjacent to it. Its dipoles will line up parallel to the applied field if the stress is high enough. This corresponds to the writing process. If a stress wave interacts with a magnetic block which is magnetized antiparallel to the applied field, the block will reverse its magnetization direction. This leads to stress waves, which will induce a voltage in the transducer. No magnetic energy release and no generation of new stress waves is expected if the field is applied parallel to the magnetization direction of the block. This is the readout process.

Sky‐Blue Pink*

ABSTRACTThe appearance of colours is affected by both instantaneous and gradual adaptations. Instantaneous adaptation can result in a projected white light looking both sky‐blue and pink when seen as shadows in superimposed orange and green light. Gradual adaptation can contribute markedly to the colour constancy of illuminants in the tungsten‐light to daylight range. In colour photographic reflection prints and projected transparencies, naming and scaling techniques have been used to determine the chromaticities of subjective grey‐points and preferred and acceptable reproductions of blue sky, green grass, and Caucasian skin. The use of haploscopic matching to determine, and Von Kries types of transformation to predict, equivalent stimuli for different adaptations is discussed: it is suggested that colour scaling is preferable to haploscopic matching because haploscopic results have been shown to be dependent on the matching technique adopted; it is also argued that, because adaptation cannot be adequately represented by a Von Kries type of transformation, equivalent stimuli are better defined by means of grids of lines of constant hue and saturation for various adaptation conditions.