Achieving high accuracy in geodetic surveys: which treatment is essential? Select the statement that best supports the higher accuracy sought in geodetic (large-area) surveys.

Introduction / Context:
Geodetic surveys cover long lines and large areas where the assumption of a flat Earth becomes invalid. To attain high positional accuracy, the computations must reflect the true geometry of the Earth, including curvature and, where required, the ellipsoidal model used for a datum.

Given Data / Assumptions:

• Survey spans are large enough that plane approximations introduce non-negligible error.
• Angles are observed between lines on a curved surface (geodesics).
• Standard geodetic reductions, including curvature and possibly refraction, are applied.

Concept / Approach:

High accuracy requires modelling the Earth as an ellipsoid (or sphere as a first approximation). Distances must be reduced to the ellipsoid; angles must consider the convergence of meridians and curvature. Plane surveying formulas can be used only after appropriate map projections and geodetic reductions are performed.

Step-by-Step Solution:

Verification / Alternative check:

National control networks universally use ellipsoidal models and geodetic reductions—evidence that curvature must be accounted for to attain sub-arcsecond accuracies.

Why Other Options Are Wrong:

Ignoring curvature or using only plane formulas leads to bias over long extents; (c) is incomplete without corrections.

Common Pitfalls:

Applying plane computations directly to geodetic observations; neglecting projection scale factors when moving to map coordinates.

Final Answer:

Account for the Earth’s curvature in angles and distances