Great Trigonometrical Survey

It was begun in 1802 by the British infantry officer William Lambton, under the auspices of the East India Company.

Everest was succeeded by Andrew Scott Waugh, and after 1861, the project was led by James Walker, who oversaw its completion in 1871.

Among the many accomplishments of the Survey were the demarcation of the British territories in the subcontinent and the measurement of the height of the Himalayan giants: Everest, K2, and Kangchenjunga.

[2][3][4] From its inception in 1600 to its domination of the entire Indian subcontinent by the beginning of the nineteenth century, the British East India Company gained more and more territory.

[1] In 1800, shortly after the Company victory over Tipu Sultan, William Lambton, an infantry soldier with experience in surveying, proposed to remedy precisely that, through a series of triangulations, initially through the newly-acquired territory of Mysore, and eventually across the entire subcontinent.

The initial baseline was measured with great care since the accuracy of the subsequent survey was critically dependent upon it.

Barrow was succeeded by Syed Mohsin from Arcot, Tamil Nadu, and after his death, the instruments were supplied by Cooke from York.

Index to the Great Trigonometrical Survey
The first triangulations across the Peninsula
Measurement of the Calcutta baseline in 1832 based on a sketch by James Prinsep . This shows surveyors stretching a chain on coffers supported on pickets. The chain is housed under shade to reduce errors due to thermal expansion, and is aligned using a boning telescope. [ a ]
A zenith sector was an upward-facing telescope with accurate angle measurement scales. A star close to the zenith of known declination from the Pole star was used to determine latitude, as a direct measurement of the pole star could be affected by refraction.
Survey towers used by George Everest to elevate the instruments
One of the survey towers in Kolkata in 2012