Automated offside systems appear to work the moment the cameras are switched on. In practice they depend on a survey of the building that has to be completed and verified days ahead of a match.
The system needs a map before it needs footage
Tracking a limb position in three dimensions requires knowing exactly where each camera sits, which way it points, and how its lens distorts the image. None of that can be inferred from the video alone.
Engineers therefore survey mounting points against fixed reference marks on the structure, then feed those measurements into the system as a fixed model of the venue. The math depends on that model being right.
An error of a few centimeters in a camera position becomes a visible error in a limb line at the far end of the field. Small survey mistakes do not stay small.
The field itself has to be measured too
The system needs the playing surface as a plane in the same coordinate space as the cameras, which means the field markings are surveyed rather than assumed from a rulebook diagram.
Fields are not perfectly flat. Most are built with a slight crown for drainage, and that curvature has to be accounted for or the plane the software projects onto sits below the actual grass.
In American venues that host multiple sports, the soccer field is often laid out differently from the markings used the week before. Each configuration is effectively a separate survey.
Multi-purpose stadiums move more than fans realize
Retractable seating sections, temporary camera platforms and stage rigging all attach to the same structure the cameras hang from. Moving them can shift a mounting point enough to matter.
Concerts are the common culprit, because heavy rigging is hung from roof steel and then removed. The structure returns close to where it started, but close is not the same as identical.
Operators therefore re-verify after any significant change in the building rather than trusting the previous survey. Verification is faster than a full survey but still cannot be done minutes before kickoff.
Verification uses known objects, not opinions
Checking the calibration means placing objects at surveyed positions on the field and confirming the system reports them where they actually are. It is a measurement test, not a visual judgment.
If the reported position drifts, the fault is usually a camera that has been knocked or a mount that has settled. Finding which one requires testing them individually.
That process takes hours and needs an empty field, which is why it happens on a non-match day rather than during warmups.
Why this shapes where the technology appears
The recurring cost is survey labor and venue access, not the software license. A stadium that is busy every day is harder to calibrate than one that hosts a single tenant.
That is part of why automated offside has spread through competitions with a small number of controlled venues first. The technology scales with building access more than with budget.
For a tournament using many stadiums across a large country, calibration is a logistics program in its own right, planned months ahead of the first match.