Short note: Photogrammetry limitation and uses

Photogrammetry is the science and art of obtaining reliable measurements, maps and three-dimensional information of objects and terrain from photographs. Aerial photogrammetry uses photographs taken from aircraft or drones, and close-range photogrammetry uses ground-based cameras.

   Camera stations O1 -------- O2
        \                      /
         \    overlap area    /
          \__________________/
              ground  -> 3D model -> map

Basic steps

1. Plan the flight and establish ground control.
2. Take overlapping photos (60 % end lap, 25–30 % side lap).
3. Process the photos, orient the stereo pairs, and measure.
4. Produce maps, DEMs, orthophotos or coordinates.

Uses

• Topographic, planimetric and contour maps of large areas.
• Engineering projects: route location, site selection for dams, bridges and airports.
• Earthwork volume and cross-section measurement.
• Cadastral surveys, land use planning and urban planning.
• Geology, forestry, agriculture and archaeology.
• Disaster management: flood and landslide mapping, damage assessment.
• Close-range work: structural deformation, monuments, accident reconstruction.

Limitations

• Costly equipment, aircraft and trained personnel; uneconomical for small areas.
• Weather dependent: clouds, haze and shadow affect photo quality.
• Ground control is still needed, and field verification of names and details is necessary.
• Dense vegetation, shadows and tall buildings hide the ground; small details may not be visible.
• Accuracy depends on scale, camera quality, tilt and relief displacement; processing needs skill.
• Boundaries and underground features cannot be seen.