Review of Geodesy for Geomatics and GIS Professionals, by James A. Elithrop Jr. and Dennis D. Findorff: Xan Edu Original Works, Ann Arbor, Mich.; 2003; ISBN l-59399-087-1. Price: $75.00.

Geodesy for Geomatics and GIS Professionals is designed as a textbook for a course that introduces the surveyor and GIS professional to coordinate systems and datums. It focuses on the three dimensionality that is essential in the modern day with the advent of GPS. This text assumes an understanding of geometry and trigonometry. A few parts require some knowledge of elementary calculus and matrix manipulation, but the bulk of the text does not. A highly valuable aspect of this book is that relevant formulas are illustrated by giving numeric solutions to example problems.

The first chapter gives definitions of the terms that will be used and a short history of geodesy. Of the remaining 11 chapters, 9 cover the basics of three-dimensional (3D) coordinates and their relation to one another, as well as definitions of modern datums and their realization through high accuracy reference stations. The other two chapters (Chapters 4 and 9) cover the Earth’s gravity field and its application to vertical datums in conventional leveling and geoid computation. The only subject not covered in the realm of coordinate systems is the conversion of 3D coordinates to map coordinates such as state plane coordinates and universal transverse mercator coordinates.

Chapter 2 begins the introduction of 3D coordinates with a discussion of latitude and longitude, including the relation of longitude and time. Chapter 3 gives an introduction to 3D geometry using the sphere as a reference surface. The relation between Cartesian and curvilinear (geographic) coordinates is given, as well as an introduction to spherical trigonometry. Skipping Chapter 4 for the moment, Chapter 5 builds on the simpler spherical coordinates give in Chapter 3 to present the more complex ellipsoidal geometry. There is a rather complete development of ellipsoidal geometry as used in geodesy.

Chapter 6 gives an aspect of 3D geometry of special importance to surveyors, the impact of three dimensionality on the Public Land Survey System (PLSS). This chapter covers such things as convergence of meridians, bearings and azimuth, and meaning of distances. Chapter 7 introduces the 3D coordinate types of interest in surveying and GIS applications, that is, geocentric Cartesian coordinates, curvilinear coordinates (latitude, longitude, and ellipsoid height), and local horizon coordinates. There is special emphasis on the conversion of one type of coordinate to another.

Chapter 8 covers national horizontal, vertical, and 3D datums the user might encounter. The vertical datums discussed are NGVD29 and the currently used NAVD88. The horizontal datum is discussed in NAD27. And the 3D datum discussed is the currently used North American Datum of 1983 (NAD83). In the case of NAD83, the improvements in the accuracy of the coordinates of stations used to realize the NAD83 are mentioned. Also covered are the methods used to transform from one datum to another and the conversions from less accurate to more accurate realizations of NAD83.

Skipping Chapter 9 for the moment, Chapter 10 discusses astronomic coordinates and the relation of astronomic coordinates to geodetic coordinates. This chapter includes an interesting discussion of the meaning of horizontal distance as determined by EDM measurements. Chapter 11 covers the basics of how the coordinates used for GPS satellites are derived. To do this the celestial reference frame is introduced.

Chapter 12 covers in greater detail than Chapter 8 the reference station networks established by the National Geodetic Survey (NGS) as it improved the accuracy of its realization of NAD83. This includes the High Accuracy Reference Networks (HARNs) and the Continuously Operating Reference Station (CORS) network. The International Terrestrial Reference System (ITRS) coordinate system and its relation to NAD83 is also presented. This chapter is a little out of date, but this is not a reflection on the authors. Rather, it is a measure of how fast the field has evolved in the last $\text{three}\text{years}$ . However, the information in this chapter provides the basics, and a knowledgeable teacher could easily bring the student up to date.

Turning now to Chapters 4 and 9. Chapter 4 presents a basic discussion of the Earth’s gravity field, gravitational potential, and equipotential surfaces. It then describes the effect of the gravity field on the results of conventional leveling. Chapter 9 covers the computation of the geoid from gravity data and the geoid models determined by NGS, including how they introduced leveling and GPS data to produce a hybrid geoid. GEOID03 is not discussed because it was introduced after the text was published.

This text presents an excellent introduction to the subject of coordinates and datums, a subject that currently is sadly lacking in coverage in the fields of surveying and GIS.