Plane and Geodetic Surveying the Management of Control Networks By Aylmer Johnson

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Plane and Geodetic Surveying the Management of Control Networks By Aylmer Johnson

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Contents

Preface ix
Acknowledgements xi
1 Introduction 1
2 General principles of surveying 5
3 Principal surveying activities 12
4 Angle measurement 24
5 Distance measurement 39
6 Levelling 44
7 Satellite surveying 53
8 Geoids and ellipsoids 68
9 Map projections 80
10 Adjustment of observations 97
11 Reduction of distance measurements 115
12 Reciprocal vertical angles 128
Appendices
A Constants, ellipsoid and projection data 135
B Control stations 137
C Worked example in transforming between ellipsoids 140
D Calculation of local scale factors in transverse Mercator projections 142
E Worked examples in adjustment 145
F Worked example in setting out 152
G Booking sheets 157
H Calculation sheets 162
Glossary 165
Bibliography 169
Index 171

Preface

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 fundamental
principles is the key to keeping abreast with the changes which technology inevitably
brings, and indeed to initiating appropriate changes, when technology makes this
possible. I hope that this book has succeeded in applying that philosophy to surveying, in
a way which will be of value to those who read it.