Great Trigonometric Survey was a project of the Survey of India from the early 1800s till the end of the 19th century. It was piloted in its initial stages by William Lambton, and later by George Everest. Among the many accomplishments of the Survey were the demarcation of the British territories in India, and the measurement of the height of the Himalayan giants - K2, Kanchenjunga and Everest. The Survey had an enormous scientific impact as well, and was responsible for the first accurate measurement of a section of an arc of longitude, and measurements of the geodesic anomaly. The tall Rajagopuram of the big temple also found use as a survey platform during the measurement of the Great Arc, by the Survey of India under William Lambton. The Great Theodolite used during the Survey of India was damaged in a fall from the roof, and its carefully calibrated plates were bent. This instrument was later repaired at Trichy.
Hi all found more matter on the trignmetric survey and the big temple from an article in frontline
a mention of the big temple in 1808
TWO HUNDRED years ago, on April 10, 1802, the British surveyor Col. William Lambton began an ambitious, audacious and mathematically meticulous scientific odyssey at St. Thomas Mount in Madras (now Chennai). It took four decades to be completed. The project ended on the foothills of the Himalayas. The Great Arc became the longest measurement of the earth's surface ever to have been attempted. The Great Arc was completed by George Everest, after whom the highest point on the earth is named. The technique of 'triangulation' involves identifying three mutually visible reference points, usually prominent hills or buildings, as the corners of a triangle. Knowing the exact distance between two of these points, and then measuring the angles made at each by the respective lines of sight with the third reference point, the distance and position of the third point can be deduced by simple trigonometry. The measurement of the Great Arc resulted in new values for the curvature of the earth throwing fresh light on the then longstanding debate on the exact shape of the planet.
the expedition was marred by an accident at Thanjavur in late 1808 when Lambton moved away from the Giant Arc to carry out a parallel triangulation further down the east cost. While trying to hoist the half-tonne theodolite atop the 217-ft gopuram of the Brihadeeshwarar temple for his angle measurements, the guy that was lifting the theodolite snapped and the instrument crashed down into a mangled mass of steel and iron. Lambton was not one who would give up so easily, nor would he wait for a couple of years for a new instrument to arrive - though he, accepting full responsibility for the mishap, had ordered a new one at his own expense. According to an account of the Great Arc, Lambton shut himself up in a survey tent for nearly six weeks and repaired it himself with help from the military workshop at Tiruchi.