Ground-Plane Calibration
Definition
A physical survey of the scene after the event, measuring reference points on the floor relative to the camera position, allowing the analyst to model the camera geometry precisely and correct for tilt and perspective in the recorded footage.
- Purpose
- Models camera geometry to correct tilt and perspective
- Method
- Post-event physical survey of floor reference points
- Reference
- Measured relative to fixed camera position
- Application
- Underpins photogrammetric height estimation from CCTV
Common questions
Why does height estimation from CCTV need ground-plane calibration at all?+
A single 2D camera image compresses depth and perspective, so an object's apparent size in pixels depends on both its real size and its distance from the lens. Ground-plane calibration supplies known real-world reference distances so the analyst can reverse this distortion mathematically rather than guess at scale.
What happens if the camera position has changed since the recording?+
The calibration becomes invalid, because it depends on measuring the scene from the exact camera geometry that produced the footage. Analysts check installation records, mounting brackets, or timestamped photographs to confirm the camera has not been moved, adjusted, or replaced before relying on a ground-plane survey.
Related terms
- Perspective Distortion Error
- The apparent change in size of objects at different distances from the camera due to projective geometry. A person closer to the...
- Pixel Height Ratio
- The number of pixels occupied by a vertical extent (person, door, markings) in the image. Ratios between subject and reference pixel heights...
- Reference-Object Method
- Height estimation by measuring the pixel heights of both the subject and a reference object of known stature in the same frame,...
- Stature Estimation Uncertainty
- The combined error from pixel localisation, reference height knowledge, positional correction accuracy, and camera model assumptions, expressed as a confidence interval at...
- Vanishing-Point Method
- Using the vertical vanishing point and two horizontal vanishing points to compute the camera's effective viewing geometry, then projecting the person's image...