Multi-camera people positioning needs three answers: whether observations refer to comparable times, how image positions map to the site, and whether different observations belong to the same person. Time alignment, ground calibration and cross-camera association address these questions separately. One working component does not establish verification of the others.
Time alignment defines comparison conditions
Check time sources, units, recorded events, transfer delays and handling of lost synchronization. Devices supporting PTP can configure clock synchronization according to their documentation. Clock synchronization alone establishes neither that different views show the same person nor that ground coordinates are correct. Check actual devices and network conditions; see the manufacturer PTP documentation for mechanisms.
Ground mapping defines geometric conditions
OpenCV homography tutorial explains projective relations between planes. Before using a ground mapping, check corresponding points, lens conditions, image dimensions and the ground model. Steps, slopes or multiple levels cannot use one plane without assessment. Use one set of points to fit the mapping. Use a different, independent set of points to check the mapping.
Association needs checks beyond time and space
| Condition | Possible clue | Conclusion not established by this condition alone |
|---|---|---|
| Nearby observation times | A possible corresponding time interval | The observations definitely belong to one person |
| Nearby ground positions | A possible corresponding area | Crossing people have been correctly distinguished |
| Similar appearance or motion direction | Candidate association evidence | A real identity has been established |
| Smoothed trajectories | Changed display or estimated variation | Absolute position error has decreased |
Record errors and unknown states separately
Keep original observations, times, source cameras, calibration versions and association results. Check people crossing, reappearance after occlusion and handovers between views. Retain unknown or pending-review status when evidence is insufficient. Do not force an identifier to continue merely to draw a continuous curve. When comparing original and processed trajectories, check whether processing delays real movement. This article provides no new accuracy, responsiveness or multi-person association test results.
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