Photogrammetry
The technique of extracting three-dimensional measurements and spatial data from overlapping photographs, used to create accurate 3D models, point clouds, and georeferenced orthophotos of buildings and structures.
Photogrammetry is the science and technology of extracting spatial measurements and three-dimensional information from photographs. By analysing multiple overlapping images of the same object or scene from different positions, photogrammetric software can calculate the position of every visible point in three-dimensional space — producing point clouds, 3D mesh models, and georeferenced orthophotos with a level of accuracy that depends on image quality, overlap, and the number of ground control points used for calibration.
In building surveying and structural inspection, photogrammetry is used to produce accurate 3D models of buildings, facades, and structures from photographs captured by drones, cameras on access equipment, or hand-held cameras. The technique has become significantly more accessible with the development of structure-from-motion (SfM) software — applications such as Agisoft Metashape, Pix4D, and RealityCapture that automate the computation-intensive matching and reconstruction process.
Drone photogrammetry is particularly powerful for building envelopes and civil infrastructure. A systematic flight over a building, capturing overlapping nadir and oblique images, can produce a dense 3D model of the exterior from which dimensions, areas, and deformations can be measured — without scaffolding, rope access, or physical contact with the structure. For bridge inspections, the ability to measure crack widths, deformations, and clearances from photogrammetric models significantly reduces the risk to inspection personnel.
The accuracy achievable with drone photogrammetry on building-scale objects is typically 10-30mm without ground control points, and 5-10mm with carefully placed and surveyed ground control. For most condition survey applications, this is adequate. For precise deformation monitoring — where changes of a few millimetres matter — a higher accuracy approach using total station or laser scanning benchmarks is required.
Photogrammetry outputs complement rather than replace 360° panoramic surveys for building inspections. The 3D model provides the spatial framework and measurement capability; the 360° panoramas provide the navigable visual record and the ability to examine surfaces in detail from inside the building.
Related Terms
A set of data points in three-dimensional space representing the surface geometry of an object or environment, typically captured by laser scanning or photogrammetry, used as the basis for as-built models and dimensional analysis.
An aerial inspection technique using unmanned aerial vehicles (UAVs) to capture photographs, video, or sensor data from positions inaccessible or impractical to reach with conventional access methods.
A survey that records the precise dimensions of a building or space, producing dimensionally accurate drawings that reflect existing conditions rather than design intent.
A digital process for creating and managing information about a building throughout its lifecycle, using a shared 3D model that contains geometric and data attributes for all building elements.
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