The Visvalingam algorithm: metrics, measures and heuristics

This paper provides the background necessary for a clear understanding of forthcoming papers relating to the Visvalingam algorithm for line generalisation, for example on the testing and usage of its implementations. It distinguishes the algorithm from implementation-specific issues to explain why it is possible to get inconsistent but equally valid output from different implementations. By tracing relevant developments within the now-disbanded Cartographic Information Systems Research Group (CISRG) of the University of Hull, it explains why a) a partial metric-driven implementation was, and still is, sufficient for many projects but not for others; b) why the Effective Area (EA) is a measure derived from a metric; c) why this measure (EA) may serve as a heuristic indicator for in-line feature segmentation and model-based generalisation; and, d) how metrics may be combined to change the order of point elimination. The issues discussed in this paper also apply to the use of other metrics. It is hoped that the background and guidance provided in this paper will enable others to participate in further research based on the algorithm

Artificial intelligence approaches to astronomical observation scheduling

Automated scheduling will play an increasing role in future ground- and space-based observatory operations. Due to the complexity of the problem, artificial intelligence technology currently offers the greatest potential for the development of scheduling tools with sufficient power and flexibility to handle realistic scheduling situations. Summarized here are the main features of the observatory scheduling problem, how artificial intelligence (AI) techniques can be applied, and recent progress in AI scheduling for Hubble Space Telescope

Computations of unsteady multistage compressor flows in a workstation environment

High-end graphics workstations are becoming a necessary tool in the computational fluid dynamics environment. In addition to their graphic capabilities, workstations of the latest generation have powerful floating-point-operation capabilities. As workstations become common, they could provide valuable computing time for such applications as turbomachinery flow calculations. This report discusses the issues involved in implementing an unsteady, viscous multistage-turbomachinery code (STAGE-2) on workstations. It then describes work in which the workstation version of STAGE-2 was used to study the effects of axial-gap spacing on the time-averaged and unsteady flow within a 2 1/2-stage compressor. The results included time-averaged surface pressures, time-averaged pressure contours, standard deviation of pressure contours, pressure amplitudes, and force polar plots

Automated observation scheduling for the VLT

It is becoming increasingly evident that, in order to optimize the observing efficiency of large telescopes, some changes will be required in the way observations are planned and executed. Not all observing programs require the presence of the astronomer at the telescope: for those programs which permit service observing it is possible to better match planned observations to conditions at the telescope. This concept of flexible scheduling has been proposed for the VLT: based on current and predicted environmental and instrumental observations which make the most efficient possible use of valuable time. A similar kind of observation scheduling is already necessary for some space observatories, such as Hubble Space Telescope (HST). Space Telescope Science Institute is presently developing scheduling tools for HST, based on the use of artificial intelligence software development techniques. These tools could be readily adapted for ground-based telescope scheduling since they address many of the same issues. The concept are described on which the HST tools are based, their implementation, and what would be required to adapt them for use with the VLT and other ground-based observatories

Problems in the design and implementation of a GKS-based user interface for a graphical information system

CISRG discussion paper ;

Adding SLIP Support to UNIX System V

SLIP (Serial Line Internet Protocal)[ROMK88][KARE86] is a means by which a serial line may be used as the data link interface for TCP/IP communication [POST80]. This document describes software which can be used to enable a computer running UNIX* System V Release 3 and equipped with the WIN3B [TWG86] software to utilize SLIP. This software is necessary to our organization since we have several UNIX machines for which no Ethernet interfaces are available and from which we would like to be able to access the campus network

Electronic Reference Options: How They Stack up in Research Libraries

Electronic reference in a variety of forms is becoming a reality in libraries today. Whether it is online, CD-ROM, or databases loaded from magnetic tapes or a combination of several options, patrons have access to more electronic resources than ever before. We recently surveyed research libraries in the U.S. and Canada to see which electronic reference options they offer. ARL libraries may not be typical because they tend to be heavy users of technology and have relatively large budgets, but they can be considered trendsetters. What these libraries are offering now will be found in all types of libraries within the next few years. Academic and other research libraries have been in the forefront of electronic database access since online searching first became available in the early 1970s. They were some of the first libraries to offer intermediary online services, and by 1979 almost half (49%) of academic research libraries offered intermediary services [1]. In the mid-1980s some research libraries added end-user online searching on systems such as BRS/After Dark or DIALOG\u27s Knowledge Index [2]. These systems usually supplemented, but did not replace, intermediary search services. CD-ROM databases were added to reference departments starting in the mid-1980s. By 1987 approximately 30% of academic libraries in the United States had databases on CD-ROM [3]. In just one more year the percentage increased to almost 60%. Although it predates even online intermediary searching, end-user searching of databases loaded on an in-house computer has become popular with the recent widespread use of online public access catalogs (OPACs). An increasing number of database producers are entering into agreements with OPAC vendors so magnetic tapes of reference databases will be compatible with a library\u27s OPAC [4]. A 1990 survey by ALA found about 8% to 35% of all academic libraries had databases loaded on their OPACs [5]. The low end was for two-year and liberal arts colleges; the high end for doctorate-granting institutions. Many research libraries now offer two or even three or four of electronic options for database searching. In May 1991 we surveyed the libraries that are members of the Association for Research Libraries (ARL) to discover how many offer each four electronic options and how the addition of each new option impacts the others. We also asked for information on what the libraries are offering now and what they plan to do in the future. This article presents the survey results and paints a factual picture of electronic reference in 1991 in ARL libraries. In addition to the facts, many respondents responded with detailed comments about how electronic reference sources are changing their libraries, their workload, and their users. In a later article we will discuss these issues based on more in-depth interviews with selected librarians

MCAM: An Application Layer Protocol for Movie Control, Access, and Management

Most of the recent work on distributed multimedia systems has concentrated on the transmission, synchronization and operating system support for continuous media data streams. We consider the integrated control of remote multimedia devices, such as cameras, speakers and microphones, to be an important part of a distributed multimedia system. In this paper we describe MCAM, an application layer architecture, service and protocol for Movie Control, Access, and Management in a computer network. The OSI Reference Model is our framework. We present the protocol data units and the Finite State Machine for our application protocol and outline the automatic generation of the implementation code for layer 7 from our formal specification. MCAM allows complete and integrated control of movie data streams and devices in a heterogeneous multimedia network

Three architectures for volume rendering

Volume rendering is a key technique in scientific visualization that lends itself to significant exploitable parallelism. The high computational demands of real-time volume rendering and continued technological advances in the area of VLSI give impetus to the development of special-purpose volume rendering architectures. This paper presents and characterizes three recently developed volume rendering engines which are based on the ray-casting method. A taxonomy of the algorithmic variants of ray-casting and details of each ray-casting architecture are discussed. The paper then compares the machine features and provides an outlook on future developments in the area of volume rendering hardware

Flexible multi-policy scheduling based on CPU inheritance

Journal ArticleTraditional processor scheduling mechanisms in operating systems are fairly rigid, often supporting only one fixed scheduling policy, or, at most, a few "scheduling classes" whose implementations are closely tied together in the OS kernel. This paper presents CPU inheritance scheduling, a novel processor scheduling framework in which arbitrary threads can act as schedulers for other threads. Widely different scheduling policies can be implemented under the framework, and many different policies can coexist in a single system, providing much greater scheduling flexibility. Modular, hierarchical control can be provided over the processor utilization of arbitrary administrative domains, such as processes, jobs, users, and groups, and the CPU resources consumed can be accounted for and attributed accurately. Applications as well as the OS can implement customized local scheduling policies; the framework ensures that all the different policies work together logically and predictably. As a side effect, the framework also cleanly addresses priority inversion by providing a generalized form of priority inheritance that automatically works within and among multiple diverse scheduling policies. CPU inheritance scheduling extends naturally to multiprocessors, and supports processor management techniques such as processor affinity [7] and scheduler activations [1]. Experimental results and simulations indicate that this framework can be provided with negligible overhead in typical situations, and fairly small (5-10%) performance degradation even in scheduling-intensive situations