SaLIS vol. 64, no. 4

December 2004

 

What does height really mean?

Part I: Introduction

Thomas H. Meyer, Daniel R. Roman, David B. Zilkoski

 

This is the first paper in a four-part series considering the fundamental question, “what does the word height really mean?” National Geodetic Survey (NGS) is embarking on a height modernization program in which, in the future, it will not be necessary for NGS to create new or maintain old orthometric height benchmarks. In their stead, NGS will publish measured ellipsoid heights and computed Helmert orthometric heights for survey markers. Consequently, practicing surveyors will soon be confronted with coping with these changes and the differences between these types of height. Indeed, although “height’” is a commonly used word, an exact definition of it can be difficult to find. These articles will explore the various meanings of height as used in surveying and geodesy and present a precise definition that is based on the physics of gravitational potential, along with current best practices for using survey-grade GPS equipment for height measurement. Our goal is to review these basic concepts so that surveyors can avoid potential pitfalls that may be created by the new NGS height control era. The first paper reviews reference ellipsoids and mean sea level datums. The second paper reviews the physics of heights culminating in a simple development of the geoid and explains why mean sea level stations are not all at the same orthometric height. The third paper introduces geopotential numbers and dynamic heights, explains the correction needed to account for the non-parallelism of equipotential surfaces, and discusses how these corrections were used in NAVD 88. The fourth paper presents a review of current best practices for heights measured with GPS.

 

Digital Bathymetric Models from Rational Profiles

Rubén Martínez Marín and Tomás Echegoyen Martín

 

This paper presents a complete methodology for the reconstruction of a digital bathymetric model from a set of scattered data. Given a set of N scattered data representing the most significant points of a bathymetric surface that have been sampled in situ over a certain area or domain, the algorithms construct a triangulation of the domain using a minimal Euclidean distance criteria with the vertices of the triangulation and the interpolated surface based on profiles obtained from the original scattered dataset. This bathymetric surface is obtained applying our methodology called “rational profiles” due to every profile being obtained from a grid which has been defined with a step as a relation of two integer numbers. The main contribution of this paper lies in two fields: the triangulation method and rational profile interpolation. We show an efficient algorithm based on a modified Delaunay triangulation called “Minimum Total Distance” (MTD), applicable locally or globally. We have also developed a new set of algorithms to generate a rational grid from the original large data set so as to produce the interpolation over the domain generating the final surface. By applying this methodology to many real samples, we have demonstrated that it is possible to achieve better running times with these new algorithms. This efficient realization of the algorithms uses adapted dynamic data structures and careful caching in an integrated framework.

KEYWORDS: Digital bathymetric models, Delaunay triangulation, scattered data, rational profile interpolation, minimum total distance (MTD), computational geometry, data structures

 

GIS Analysis System for Investigating Sulphide Mineralization in South Sinai, Egypt

Hesham Abd-El Monsef, Mohammed El-Ghawaby, and Scot Smith

 

Irregularity of geological variables over adjacent rock units makes the standardization and the continuity of base metal spatial distribution uncertain. Previous approaches to predict preferable locations of mineral occurrence had often been based on systematic data-grid-network sampling. The St. Catherine region in south Sinai has moderate deposits of sulphide mineralization. Comprehensive studies of sulphide mineralization found in the area provide evidence that this mineralization is controlled by three factors: (1) base-metal concentration distribution, (2) structure alteration and (3) intensity. Variables of each controlling factor have been represented by vector layers and then integrated and analyzed using a geographic information system to produce mineral potential maps for the study area. Variables of each controlling factor were analyzed for each rock type individually. This approach was used to overcome problems due to the geochemical irregularities of various rock units. Field verification of the integrated mineral potential maps confirmed the presence of copper sulphide in the vicinity of St. Catherine. It was concluded that the maps could be used to define suitable locations for sulphide mineralization exploration.

 

The Global Land Information Explosion:

GIS-ACSM-GLIS-GSDI-GITA-URISA-GE and the Atlantic Institute

Gunther Greulich

 

In America, the label Geographic Information Systems, or GIS for short, has quickly replaced the somewhat awkward title “Multipurpose Cadastre,” which had been assigned to a 1980 study by the National Research Council. American and Canadian land data specialists, such as geodesists, surveyors, and cartographers, developed the new land management tool and were joined by other related disciplines, which all recognized the enormous potential of GIS. Several national and international organizations, devoted to GIS, have sprung up in recent years.  Even in Europe, which has nearly a 300-year tradition of land recording and management under the heading of “Cadastre,” the term has been embraced and inspired new coordinated developments. Early on, one particular organization, The Atlantic Institute, has focused on building and maintaining a professional GIS bridge between USA/Canada and Europe. In the USA, state governments have begun to create their own unique GIS, often inspired and prompted by local visionary land surveyors. GIS is growing worldwide and will be unstoppable.

 

The Struve Geodetic Arc

 J. R. Smith

 

In 1812, F.G.W. Struve, Professor of Mathematics and Astronomy at the University of Dorpat (now called Tartu), was put in charge of a trigonometrical survey in Livonia. The survey was controlled by a baseline on the ice of Lake Werz-Jerw, measured in 1819 (Metz 2002; Batten 1988). Then during 1820, Struve assisted Gauss and Schumacher in a base measure  made near Braack. This work enabled Struve to interest officials in the idea of a meridian arc of about three-and-half degrees between Gögland, an island in the Gulf of Finland, and Jacobstadt to the south. After getting the resources he was able to observe the arc between 1821 and 1831. During more or less the same period (1816-1828), Carl Tenner was doing similar work further south in Lithuania, but at that stage he was operating quite independently from Struve (Figures 1 and 2).

Once he had completed his early surveys, Struve was keen to extend the measurements further north and south so that a very long line would result and could be the basis of a sound set of values for the Earth parameters, as well as for other uses. He would have been aware of the work at that time in India by Lambton and Everest (Smith 1999), and that this work would be an ideal partner to anything he did in Russia, to determine the Earth’s parameters.

 

ABET and ACSM—A Symbiotic Relationship

Jim Plasker

 

ABET, Inc., is a federation of about thirty professional and technical societies representing the fields of applied science, computing, engineering, and technology.  The Nation’s sole recognized accrediting body for college and university programs in these fields, ABET, was originally established in 1932 as the Engineers’ Council for Professional Development (ECPD)—a “joint program for upbuilding engineering as a profession.” Among the most respected accreditation organizations in the U.S., ABET has provided leadership and quality assurance in higher education for more than seventy years. 

   ABET currently accredits some 2,500 programs at more than 550 colleges and universities nationwide.  Upwards of 1,500 dedicated volunteers participate annually in ABET activities.  ABET also provides leadership internationally, through agreements such as the Washington Accord, and offers educational credentials evaluation services to those educated abroad through Engineering Credential Evaluation International.

   Seven professional societies founded the organization and contributed to its original direction and focus: the American Society of Civil Engineers (ASCE), the American Institute of Mining and Metallurgical Engineers (now the American Institute of Mining, Metallurgical, and Petroleum Engineers), the American Society of Mechanical Engineers (ASME), the American Institute of Electrical Engineers (now IEEE), the Society for the Promotion of Engineering Education (now ASEE), the American Institute of Chemical Engineers (AIChE), and the National Council of State Boards of Engineering Examiners (now NCEES). Within its first year of existence ECPD developed itself as an accreditation agency and, in 1936, evaluated its first engineering degree programs. Ten years later, the Council began evaluating engineering technology degree programs. 

   The American Congress on Surveying (ACSM)  joined ECPD as a Participating Body in the late 1970s, and the first surveying program, California State University, Fresno, was accredited in 1979. Today, twenty-five surveying programs are accredited across the U.S.

In 1980, ECPD was renamed the Accreditation Board for Engineering and Technology (ABET) in order to more accurately reflect its emphasis on accreditation; the organization continues to put most of its emphasis on accreditation. 

    In 1997, following nearly a decade of development, ABET began adoption of outcomes-based criteria, which were considered at the time a revolutionary approach to accreditation.  The revolutionary aspect of outcomes-based criteria was the focus on what is learned rather than what is taught. At its core was the call for a continuous improvement process informed by the specific mission and goals of individual institutions and programs. Lacking the inflexibility of earlier accreditation criteria, outcomes-based criteria meant that ABET could enable program innovation rather than stifling it, as well as encourage new assessment processes and subsequent program improvement.