Which technique is used to establish elevations on project control points?

• A. Barometric leveling
• B. Single-epoch GNSS only
• C. Differential leveling techniques
• D. Trigonometric leveling

Answer: (C)

Establishing elevations on project control points relies on measuring vertical differences with high precision, and the method designed for that is differential leveling. In this approach, a level and a graduated staff are used to take back-sight and fore-sight readings as you move from one point to the next, then compute the height differences and transfer elevations from a known benchmark to the new points. Repeated measurements and careful sequencing minimize instrument errors and refraction effects, providing a reliable height network that ties all points to a common datum.

Barometric leveling estimates height changes from atmospheric pressure, but weather conditions and air-density variations introduce errors that make it unsuitable for precise control elevations. A single GNSS epoch can give height information, but relying on one epoch yields insufficient accuracy for a network of control points without additional sessions and complex gravity/geoid corrections. Trigonometric leveling uses angles and slope distances to infer vertical differences but is more sensitive to measurement errors and refraction, and generally less precise than differential leveling. For the most accurate and dependable elevations on project control points, differential leveling techniques are used.