Plane and Geodetic Surveying

Abstract

More than almost any other engineering discipline, surveying is a practical, hands-on skill. It is impossible to become an expert surveyor, or even a competent one, without using real surveying instruments and processing real data. On the other hand, it is undoubtedly possible to become a very useful surveyor without ever reading anything more theoretical than the instrument manufacturers’ operating instructions. What, then, is the purpose of this book? A second characteristic of surveying is that it involves much higher orders of accuracy than most other engineering disciplines. Points must often be set out to an accuracy of 5 mm with respect to other points, which may be more than 1 km away. Achieving this level of accuracy requires not only high-quality instruments, but also a meticulous approach to gathering and processing the necessary data. Errors and mistakes which are minute by normal engineering standards can lead to results which are catastrophic in the context of surveying. Yet in the real world, errors will always exist and approximations and assumptions must always be made. The accepted techniques of surveying have been developed to eliminate those errors which are avoidable, and to minimise the effects of those which are not. Likewise, the formulae used by surveyors incorporate many assumptions and approximations, and save time when the errors which they introduce are negligible by comparison with the errors already inherent in the observations. No two jobs in surveying are exactly the same. A competent professional surveyor therefore needs to know the scope and limitations of each surveying instrument, technique and formula—partly to avoid using unnecessarily elaborate methods for a simple job, but mainly to avoid using simplifying assumptions which are invalidated by the scale or required precision of the project. This knowledge can only be developed by understanding how the accepted techniques have evolved, and how the formulae work— and this understanding is becoming increasingly hard to acquire with the advent of electronic ‘black box’ surveying instruments and software applications, which perform elaborate calculations whose details are hidden from the user. It is this understanding which this book sets out to provide. The methods for using each generic class of surveying instrument have been described in a way which is intended to show why they have evolved, and the calculations are similarly explained, such that the inherent assumptions can be clearly identified. Wherever necessary, practical guidance is also given on the range of distances for which a particular formula or technique is both necessary and valid. The material in this book is based on the surveying courses taught in the Engineering Department at Cambridge University, and I am grateful to the many colleagues who have both enhanced my own understanding of the subject and contributed to past editions of the ‘Survey Notes’, from which this book has evolved. The philosophy of engineering education at Cambridge has always been that an understanding of a subject’s fundame