The Survey Revolution

including a few which were still only a gleam in someone's eye. I will try to weave together three main strands into a tapestry which will illustrate how some of the main scientific and technical discoveries of this century?this is the first strand?have revolutionized surveying and mapping. The second strand is the different techniques used in our profession; and the third is the different users and how they have been affected. I shall concentrate on the effects of these changes, rather than try to explain in detail how they operate. Obviously the principal relevant discoveries have been in mathematics and physics; but I want also to look at changes in the human side of our profession. As many of you know, survey and mapping can be divided into six main processes?global positioning, the framework, detail survey, height determination, computing and cartography?and I propose to use these as the main strand on which to hang the others, showing how the basic inventions have influenced them. For example, electronics have revolutionized distance measurement and computation; rockets and radio global positioning and remote sensing; and photography and flying, detailed mapping. The third strand includes the various users: geophysicists, geodesists and soldiers interested in the overall shape of the earth, geographers in its natural and man-made surface features, engineers in the precise spatial data required for the design and construction of projects; navigators requiring sea and air charts and global positioning; and property owners and their agents interested in land parcels and their boundaries. The framework I begin with the framework because this now provides global positioning instead of the other way round. For several centuries frameworks have been based on that simple and strong figure the triangle, as of course have many structures like house roofs, bridges and pylons. Compare the main triangulation of India, with its chains of quadrilaterals, with the framework of Tower Bridge; or our own triangulation with an electricity pylon. Three observed angles of each triangle provide an immediate check. It is only when triangulation was impossible that we resorted to traverse, with every leg measured laboriously on the ground with a tape?and how we hated it! Not only was it very tedious and slow; but when a traverse failed to close the error was difficult to locate, and there was the survey equivalent of weeping and gnashing of teeth. Thus the biggest recent change in framework techniques has been the invention of quick, easy and accurate distance measurement. Curiously, we have reverted to the very earliest stages of surveying, when all measurements were of distance by tape or chain. Currently distances can be measured instantaneously varying from a few feet to thousands of miles, by the very accurate timing of the passage of electro-magnetic radiation in the form of radio, light, micro-wave or infra-red radiation, by what we call electro-magnetic distance measurement (EDM). We have the Geodimeter using light, and the South African Tellurometer, using micro-waves which give accurate distances up to 60 miles. The Wild D 110 was the first surveyor's instrument using infra-red for measuring distances from a few feet up to a ?> John Wright gave his first lecture to the Society in 1934, since when he has had distinguished careers with the Sudan Survey Department, Hunting Air Surveys Limited, and the Directorate of Overseas Surveys. He is currently writing a long article on Mapping and Surveying for the Encyclopaedia Britannica. This lecture was delivered at a meeting held on 24 February 1986 in the Society's House, with Lord Shackleton in the Chair

Geography · Advanced Mathematical Theories · Optics and Image Analysis

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