The Great Trigonometrical Survey of India: Demarcation of the Indian Subcontinent.

The Great Trigonometrical Survey (GTS) of India was one of the most ambitious scientific projects of its time, aiming to create a comprehensive and accurate survey of the Indian subcontinent. The article provides an in-depth examination of the GTS, highlighting its history, methods, achievements, and impact.

Historical Context of the Great Trigonometrical Survey:

• British East India Company Expansion: From 1600, the British East India Company expanded its territories in India, acquiring more land through military conquests and treaties.
• Need for Accurate Maps: As the East India Company gained more territory, it became essential to have accurate maps for administration, military operations, and revenue collection.
• Initial Surveys: Early surveys, such as those by James Rennell in Bengal, revealed a lack of precise measurements, underscoring the need for a more accurate geodetic approach.

Inception and Leadership:

• In 1800, William Lambton, a British infantry officer with experience in surveying, proposed a comprehensive trigonometric survey to map the Indian subcontinent accurately.
• The Great Trigonometrical Survey (GTS) began on 10 April 1802 with the measurement of a baseline near Madras.
• The baseline was 7.5 miles (12.1 km) long and was carefully measured to ensure accuracy.
• Triangulation Chains: The Great Trigonometrical Survey (GTS) used triangulation chains to create a “gridiron” of survey lines, running from north to south and east to west.

Key Figures in The Great Trigonometrical Survey (GTS) of India

William Lambton:

• Initiated the Great Indian Trigonometrical Survey (GTS) in 1802.
• Established the first baseline near Madras and laid the groundwork for the triangulation network across India.

George Everest:

• Succeeded Lambton in 1823 and expanded the survey northward.
• Renowned for his meticulous approach, ensuring the survey's accuracy and reliability.
• Had the world's tallest peak, Mount Everest, named in his honor.

Andrew Scott Waugh:

• Followed Everest as Surveyor General of India.
• Oversaw significant portions of the GTS
• Identified Peak XV, later named Mount Everest.

James Walker:

• Took over the leadership after Waugh and completed the GTS in 1871.
• Oversaw the final stages of the survey and contributed to its reorganization and consolidation.

Radhanath Sikdar:

• An Indian mathematician and surveyor associated with The Great Trigonometrical Survey (GTS).
• Known for calculating the height of Peak XV (he was the first to calculate the height of Mount Everest, the world's highest mountain peak) using trigonometry, making him one of the earliest to recognize it as the tallest peak in the world.

Nain Singh Rawat:

• A prominent Indian surveyor known as a “pundit.” Conducted detailed surveys in Tibet, where European surveyors were not allowed.
• He walked around 1580 miles to discover an unexplored part of Tibet.
• Known for his meticulous recording of geographical and cultural details during his surveys.
• His contributions to the GTS included mapping previously unexplored regions and collecting valuable data on Tibetan culture and geography.

Kishan Singh Rawat:

• Cousin to Nain Singh Rawat and also an important “pundit.”
• Carried out surveys in remote and restricted areas, providing essential information to the GTS.
• Contributed to the mapping of parts of Tibet and other challenging regions. Like his cousin, Kishan Singh gathered data that was critical for the success of the Great Trigonometrical Survey.

Instruments and Methods

• Theodolites and Zenith Sectors: The Great Trigonometrical Survey (GTS) used large, high-precision theodolites made by William Carey and zenith sectors made by Jesse Ramsden. Later surveys used more compact theodolites.

• Measurement Techniques: To ensure accuracy, the baseline was measured with an especially accurate folding chain, laid on horizontal tables and shaded from the sun. Constant tension was maintained throughout the measurement process.
• Temperature Corrections: Temperature variations were accounted for during baseline measurement, as they could affect the length of the chains.
• Instrument Manufacturing: George Everest supervised the construction of instruments, leading to the establishment of an instrument company in Calcutta by Henry Barrow.

Challenges and Corrections

• Geographical Challenges: The survey faced diverse and challenging terrain, including dense forests, rivers, and mountainous regions.
• Climatic Conditions: Extreme weather, including monsoons and scorching heat, posed risks to the surveyors.
• Corrections Applied: To achieve the highest accuracy, various corrections were applied:
• Earth’s Curvature: The curvature of the Earth was accounted for in distance calculations.
• Non-Spherical Nature of the Earth: The non-spherical curvature was also considered.
• Gravitational Influence: The gravitational pull of mountains affected pendulums and plumb lines, requiring correction.
• Refraction: Refraction due to atmospheric conditions was another factor requiring adjustment.
• Height Above Mean Sea Level: This correction accounted for variations in altitude across different survey points.

Achievements and Legacy

• Demarcation of British Territories: The GTS played a crucial role in demarcating British territories in India, providing accurate maps for administration and governance.
• Measurement of the World's and Himalayas' Highest Peaks: The survey measured the height of major Himalayan peaks, including Everest, K2, and Kangchenjunga.
• Scientific Contributions: The GTS provided one of the first accurate measurements of a section of an arc of longitude and contributed to the development of theories related to isostasy.
• Pundits and Native Surveyors: The GTS employed native surveyors called “pundits,” including Nain Singh Rawat and Krishna Singh Rawat, who played a vital role in surveying areas where Europeans were not permitted, such as Tibet.

Reorganization and Amalgamation

• Reorganization of Surveys: In 1875, the budget for the GTS was reduced, leading to a reorganization that amalgamated the Great Trigonometrical Survey, the Topographical Survey, and the Revenue Survey into a single entity, the Survey of India.
• Continued Impact: Despite the reorganization, the GTS had laid the groundwork for modern geodesy and influenced the development of surveying practices worldwide.

Survey of India celebrates 250 years of its Glorious History (Video)

The GTS not only demarcated British territories and measured Himalayan peaks but also contributed to the advancement of geodetic knowledge and laid the foundation for modern surveying in India and beyond.