The Kalianpur 1975 Datum
The Survey of India historically relied on the Kalianpur 1975 datum (EPSG:4146), which uses the Everest 1830 ellipsoid. The origin point is in Kalianpur, Madhya Pradesh. Because the Everest 1830 ellipsoid is a local best-fit for the Indian subcontinent and is not geocentric, Kalianpur coordinates differ significantly from WGS84.
The shift between Kalianpur 1975 and WGS84 ranges from 5 to 10 meters depending on the location within India. Overlaying un-transformed Kalianpur 1975 cadastral maps onto modern Google Earth (WGS84) imagery results in visible boundary misalignment.
Transition to IGRS
To modernize spatial data for the Digital India initiative and national drone mapping, the government is transitioning to the Indian Geodetic Reference Frame (IGRF/IGRS), which is aligned with the globally-centric ITRF (like WGS84).
Engineering Risk in India
Legacy infrastructure (railways, older highways, pipelines) often possesses centerline data recorded in Kalianpur 1975 or earlier local datums. When modern drone surveys (native WGS84) are integrated during expansion projects without a rigorous 7-parameter or grid-based datum transformation, the resulting 10-meter offsets cause right-of-way land acquisition disputes and alignment clashes.
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