Applications of triangulation surveys: for which purposes are triangulation networks commonly executed in civil and geodetic practice?

Introduction / Context:
Triangulation—establishing a framework of intervisible stations measured by angles and selected distances—has long been a backbone of control surveying. Even with modern GNSS, triangulation concepts inform network design, redundancy, and quality assurance.

Given Data / Assumptions:

• Large-area mapping requires a control skeleton.
• Photogrammetry needs ground control for absolute orientation.
• Engineering projects demand precise positioning of critical points.

Concept / Approach:
By forming a connected network of triangles (often strengthened by braced quadrilaterals), triangulation yields precise coordinates of control points. These control points support topographic mapping, aerial triangulation in photogrammetry, and the layout of linear infrastructure (tunnels, bridges, pipelines) where opposing works must meet with minimal positional error.

Step-by-Step Solution:
Large-area control: triangulation densifies a national datum into regional/local frameworks.Photogrammetry: control points tie aerial photos to ground, enabling accurate stereo-compilation.Engineering works: fixed control enables transfer of alignment and grade over long distances and through difficult terrain.

Verification / Alternative check:
Historical and current surveying standards list these as principal uses; many agencies still specify triangulation-derived or GNSS-supported control prior to mapping and construction.

Why Other Options Are Wrong:
Each listed application is valid; restricting to a subset would be incomplete.

Common Pitfalls:
Assuming GNSS removes the need for geometric checks; in practice, hybrid networks improve reliability.

Final Answer:
All the above