Photogrammetry is the science of measuring from photographs. Overlapping images taken from different positions record parallax — the apparent shift of objects between views — and from that geometry, rigorous mathematics reconstructs precise 3D coordinates. It is the discipline behind topographic mapping from aerial photos for a century, and behind today’s drone mapping and 3D city models.
The geometry that makes it work
Each photograph is a bundle of rays through the camera’s perspective centre. When two or more rays to the same ground feature intersect, the feature’s 3D position is fixed. Scale and orientation come from camera calibration, precise exposure positions, and ground control points.
Aerial triangulation is the industrial version: a block of thousands of images adjusted simultaneously so all rays intersect consistently — with statistical outputs (sigma naught, RMSE at checkpoints) that certify the block’s accuracy before any product is derived.
Classic stereo and modern dense matching
Traditional stereo compilation had operators viewing image pairs in 3D and digitising planimetry, breaklines and spot heights — still the quality benchmark for engineering mapping. Modern pipelines add dense image matching: algorithms correlate nearly every pixel between views, generating photogrammetric point clouds and surface models that rival LiDAR density on textured surfaces.
The limits are physical: matching fails on uniform surfaces, water and moving vegetation, and only LiDAR penetrates canopy to bare ground.
Deliverables and accuracy
Standard products include digital surface and terrain models, true orthophotos, planimetric feature compilation, 3D building models and reality meshes. Accuracy scales with flying height, image resolution, calibration and control: from centimetres in drone blocks to the specified classes of national mapping standards (ASPRS accuracy classes, NMAS heritage).
The professional discipline is the accuracy report — checkpoints, residuals and adjustment statistics — that turns pretty outputs into certified measurement.
Frequently asked questions
What is the difference between photogrammetry and LiDAR?
Photogrammetry reconstructs 3D from overlapping images — needing texture and light, capturing photorealistic surfaces cheaply. LiDAR measures range directly with lasers — indifferent to texture, able to reach ground beneath vegetation. Many projects fly both.
What is aerial triangulation?
The simultaneous adjustment of an entire image block so every ray intersects consistently, anchored by ground control — the step that establishes a project’s geometric accuracy before maps, DEMs or orthos are produced.
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