Homography
Definition
A 3x3 projective transformation matrix that maps one plane to another. For a flat scene (a floor, a wall, a road surface), a homography between the image plane and the scene plane allows direct measurement of objects lying on that plane.
- Matrix size
- 3x3 projective transformation
- Applies to
- Mapping between two planes
- Use case
- Measuring objects on a flat scene surface
- Field
- Forensic photogrammetry
Common questions
What real-world condition does a homography require to give accurate measurements?+
The points being measured must lie on the same flat plane that was used to compute the homography, such as a road surface or floor. Objects with height above that plane will be distorted if measured with the same transformation.
How is a homography typically calculated for a scene in forensic photogrammetry?+
It is computed from at least four known correspondences between points visible in the image and their real-world coordinates on the plane, such as lane markings of known width or a surveyed reference grid placed at the scene.
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