Mapping of tunnels can be done by photogrammetric method with aid of which technique?

• A. Oblique Photography
• B. Photostat
• C. 3 Color Process
• D. Stereoscopic Vision

Answer: (A)

When mapping a tunnel with photogrammetry, how you capture the images matters because you need coverage of the curved walls, ceiling, and floor plus enough parallax between photos to derive accurate 3D coordinates. Oblique photography accomplishes this by shooting at an angle to the tunnel axis rather than straight along or directly perpendicular to a surface. That angled view reveals the tunnel’s circular cross-section and side walls clearly in a single shot, while still allowing overlapping views along the tunnel length. With proper overlap, the stereo pairs created from these oblique images provide the depth information needed to reconstruct precise 3D positions of features along the tunnel, enabling accurate mapping of the tunnel’s alignment and cross-sections. Other options either describe older or unrelated processes or refer to how depth is viewed rather than how the photographs are taken, which is why oblique photography is the best-fitting technique for this photogrammetric context.