Mapping of tunnel can be done by photogrammetric method with the aid of

• A. Aerial photography
• B. Oblique photography
• C. Stereophotography
• D. Thermal imaging

Answer: (B)

Oblique photography is used because it places the camera at a tilt that captures the tunnel’s sidewalls and ceiling, providing the necessary perspective and parallax to measure the interior geometry. This view lets you record the cross-sectional shape and the longitudinal profile as you move along the tunnel, enabling accurate 3D reconstruction with photogrammetry when paired with known scale or control points. Aerial photography isn’t suitable for enclosed spaces, as it won’t show the interior geometry; stereophotography can yield 3D data but requires precise stereo setups and still benefits from the oblique perspective to cover all surfaces; thermal imaging records heat patterns rather than precise structural dimensions.