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Gunter's chain was introduced in 1620 by English mathematician Edmund Gunter, which enabled plots of land to be accurately surveyed and plotted for legal and commercial purposes. Table of Surveying, 1728 Cyclopaedia In the 18th century, modern techniques and instruments for surveying began to be used. The modern theodolite, a precision instrument for measuring angles in the horizontal and vertical planes, was introduced by Jesse Ramsden in 1787. He created his great theodolite using a very accurate dividing engine of his own design. Earlier, more primitive devices, had been invented by Leonard Digges, Joshua Habermel and Jonathan Sisson[4] in the previous centuries, but Ramsden's theodolite represented a great step forward in the instrument's accuracy. William Gascoigne invented an instrument that used a telescope with an installed crosshair as a target device, in 1640. James Watt developed an optical meter for the measuring of distance in 1771; it measured the parallactic angle from which the distance to a point could be deduced. The modern systematic use of triangulation was introduced by the Dutch mathematician Willebrord Snell, who in 1615 surveyed the distance from Alkmaar to Bergen op Zoom, approximately 70 miles (110 kilometres), using a chain of quadrangles containing 33 triangles in all. Snell calculated how the planar formulae could be corrected to allow for the curvature of the earth. He also showed how to resection, or calculate, the position of a point inside a triangle using the angles cast between the vertices at the unknown point. These could be measured much more accurately than bearings of the vertices, which depended on a compass. This established the key idea of surveying a large-scale primary network of control points first, and then locating secondary subsidiary points later, within that primary network. Between 1733 and 1740 Jacques Cassini and his son César Cassini undertook the first triangulation of France, including a re-surveying of the meridian arc, leading to the publication in 1745 of the first map of France constructed on rigorous principles. A map by the survey, produced in 1870 Triangulation methods were by now well established for local mapmaking, but it was only towards the end of the 18th century that detailed triangulation network surveys were established to map whole countries. A team from the Ordnance Survey of Great Britain, originally under General William Roy began the Principal Triangulation of Britain using the specially built Ramsden theodolite in 1783. This survey was finally completed in 1853. The Great Trigonometric Survey of India, which ultimately named and mapped Mount Everest and the other Himalayan peaks, was begun in 1801. The Indian survey had an enormous scientific impact; it was responsible for one of the first accurate measurements of a section of an arc of longitude, and for measurements of the geodesic anomaly. Surveying became a professional occupation in high demand at the turn of the 19th century with the onset of the Industrial Revolution. Surveyors were used on industrial infrastructure projects, such as canals, roads and rail, and the profession developed increasingly accurate instruments to aid its work. Napoleon Bonaparte founded Continental Europe's first cadastre in 1808. This gathered data on the number of parcels of land, their value, land usage and names. This system soon spread around Europe. Because of the fundamental value of land and real estate to the economy, land surveying was one of the first professions to require Professional Licensure. In many jurisdictions, the land surveyors license was the first Professional Licensure issued by the state, province, or government. |
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