Camera Calibration
Definition
The process of determining the camera's intrinsic parameters: focal length, principal point, and lens distortion coefficients. Calibration can be done from a target of known geometry (e.g., a checkerboard), or estimated from scene constraints.
- Key parameters
- Focal length, principal point, lens distortion coefficients
- Common target
- Checkerboard pattern of known geometry
- Alternative
- Estimation from scene constraints (known reference lengths)
- Field use
- Photogrammetric height and distance estimation from CCTV
Common questions
Why does calibration matter for CCTV height estimation?+
Lens distortion and an unknown focal length bend straight lines and distort scale near the frame edges. Without correcting for these, a person's estimated height from footage can be off by several centimetres, enough to weaken or exclude a comparison.
Can a camera be calibrated after the recording was made?+
Yes, if the same camera and lens setting are still available, or if the scene itself contains objects of known, measurable dimension. This scene-constraint approach is common in casework where the original camera can no longer be tested directly.
What happens if calibration is skipped?+
Measurements taken from the footage carry unquantified error, which a court or opposing expert can challenge. Reporting a height or distance without a calibration step undermines the reliability of the estimate.
Related terms
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- Projective Geometry
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- Structure-from-Motion (SfM)
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- Uncertainty Propagation
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- Vanishing Point
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