Orthophoto
Definition
A geometrically corrected aerial or close-range photograph from which the distortions caused by camera tilt and terrain relief have been removed, so that measurements of distance and area can be made directly on it as if it were a plan.
- Correction applied
- Removes camera tilt and terrain relief distortion
- Source
- Aerial or close-range photograph
- Property gained
- Direct measurability as a plan
- Related to
- Orthomosaic (multi-image version)
Common questions
What is the practical difference between an orthophoto and an orthomosaic?+
An orthophoto is typically a single corrected image, while an orthomosaic is assembled from many overlapping orthophotos stitched into one continuous, consistently scaled image covering a larger area, such as an entire outdoor crime scene photographed by drone.
Why can a raw, uncorrected photograph not be used directly for scene measurement?+
An uncorrected photograph shows perspective distortion, where objects closer to the camera appear larger and features at the edges are skewed relative to those at the centre, so distances and areas measured directly on it would be inaccurate. Removing that distortion is exactly what the orthorectification process does.
Related terms
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- Ground Control Point (GCP)
- A physical marker in the scene whose three-dimensional coordinates have been measured independently by total station or GPS. Assigning those coordinates to...
- Reprojection Error
- The distance in pixels between where the photogrammetry software predicts a feature point should appear in each photograph (based on its estimated...
- Structure-from-Motion (SfM)
- A photogrammetric technique in which overlapping images from a drone or camera, processed by software, generate a three-dimensional point cloud and textured...
- Terrestrial Laser Scanning (TLS)
- A ground-based 3D LIDAR survey instrument that captures millions of range measurements per scan to produce a millimetre-accurate point cloud of the...