/ Satoshi Nishimura / Assistant Professor
/ Veronique Martin-Lang / Visiting Researcher
The Computer Graphics Laboratory is currently working on the following research projects:
1. Parallel architecture for polygon rendering and volume visualization Parallel processing is one of the most powerful ways for improving the processing speed of computers. Especially in the area of computer graphics, many researchers have been trying to apply the techniques of parallel processing to various problems. There are three reasons for this research:
In the Computer Graphics Laboratory, we have a parallel graphics machine called the VC-1 which was developed by Prof. Nishimura, one of the members of our laboratory. The VC-1 comprises 16 processing elements each of which contains the Intel i860 processor.
One of the current research directions is the extension of the VC-1 architecture so that anti-aliasing is fully supported. We are also planning to add special hardware for rasterization to the VC-1 architecture to improve polygon rendering performance.
Another research direction is to develop a parallel machine for real-time volume rendering. Volume rendering is particularly important in medical applications. We are planning to develop scalable hardware including a special chip for trilinear interpolation and alpha-blending.
2. Surface reconstruction, geometric modeling through shape information
Shape of 3-dimensional objects is a concept of fundamental importance for description, analysis and representation. Our aim is to extract shape information from real data and more precisely from Noh masks in order to develop a shape-based geometric modeling environment. We developed several algorithms of extraction of shape features based on curvature extrema (ridges and ravines) for surfaces defined by height functions. An extension to triangulations is under study. We are currently focusing on reconstruction algorithms from scattered data in order to construct a triangulation of the scanned masks. One method uses the particularities of the scanner whereas the other one is based on the Delaunay triangulation and a boundary extraction algorithm.
We are also involved in a topology-based geometric modeling project. Our study of a geometric modeling environment based on simplicial sets led us to the definition of operations for the manipulation of triangular patches. In particular, we defined a cartesian product of triangular Bezier patches.
Refereed Proceeding Papers
The VC-1 is a parallel graphics machine for polygon rendering based on image composition. This paper describes the architecture of the VC-1 along with a parallel polygon rendering algorithm for it. The structure of the VC-1 is a loosely-coupled array of 16 general-purpose processors, each of which is equipped with a local frame buffer. The contents of the local frame buffers are merged in real time for generating the final image. The local frame buffers are virtualized with a demand-paging technique, by which the image memory capacity for each local frame buffer is reduced to one eighth of full-screen capacity. Polygons are rendered in either pixel parallel or polygon parallel depending on the on-screen area of each polygon. The real performance of the VC-1 as well as estimated performance for systems with up to 256 processors is shown.
We propose fast algorithms for the detection of view-independent ridges on surfaces defined by graphs of functions. The ridges are defined via extrema of the principal curvatures along the associated principal direction. These algorithms have the advantage to be fast and it appears that the so-defined ridges deserve as a characteristic feature of the shape of the surface. Results on several analytic surfaces are shown and discussed.
This paper deals with topology based geometric modeling and more precisely with the usage of simplicial sets as a combinatorial representation of triangular subdivisions. We focus on the definition of the cartesian product which is the base of many topological constructions and which extends extrusion to any dimension. The cartesian product of two simplicial sets is well-defined in algebraic topology. We present some combinatorial properties of this operation which lead us to an algorithm implemented in the modeler. We also define a cone operation and deduce a second definition of the cartesian product. Finally, we compare the two construction methods induced by the two definitions of the cartesian product.
This work fits into the domain of topology-based geometric modeling. An assembling of non-overlapping patches can be interpreted as a subdivision of a geometric object into cells of different dimensions and a combinatorial structure can be associated with it. More precisely, our study deals with the manipulation of simplicial sets imbedded on triangular patches. We give the definition and properties of simplicial sets and triangular Bezier spaces and discuss the relationship between these two entities. The advantages of this approach are developed and some construction operations for the manipulation of this structure are presented.
Unrefereed Papers
Technical Reports
Satoshi Nishimura, Overview of the Practical Music Macro Language (Both in Japanese and English), Numbers 97-1-004 and 97-1-005. The University of Aizu, March 1997.