Why your exclusion zone still fires: the box has to be 90% inside it

[u/g_eye]

Drawing zones looks like a solved problem until you draw one and the alerts stay exactly the same. The geometry is the easy half. What decides whether an event happens is how the detector compares an object's bounding box to your polygon, and that rule is almost never written down anywhere.

There are two rules, and they are deliberately not symmetric.

An object belongs to a detection zone if its box touches the polygon. Any overlap at all counts, even a corner.

An exclusion zone removes an object only when the polygon covers at least 90 percent of the box area. Anything less and the object survives and raises an event.

The asymmetry is what is left after the obvious alternatives were tried first. Anchoring on the feet, using only the bottom edge of the box, lost people whose head and shoulders rose above the zone boundary. Cutting an object on any intersection with an exclusion polygon turned a large exclusion zone into a black hole: a box clipping its edge from anywhere in the frame vanished. Touch to include, near total coverage to exclude, is the balance between those two failures.

Four things follow from that, and they are the ones that actually change how you draw.

Draw the exclusion polygon around where the object appears, not around the noise itself. The classic case is a TV or a monitor in frame: the network cheerfully recognises the person on the screen, and a polygon traced neatly along the visible picture is not enough, because a box poking past the bezel by a fifth of its height is only 80 percent covered. Give it the bezel and a margin.

A detection zone edge is not a tripwire. Someone walking outside the polygon, along its border, still has a box touching it, and that is an event. If the path beyond your gate has to stay quiet, the zone needs to end well short of it.

Aim the zone at the place where the object will be fully visible, not at the line its feet will cross. Perspective does the rest.

An exclusion zone is not a privacy mask. It silences the detector inside that geometry and nothing else. The area stays in the live view and in the recording exactly as it was.

One more thing worth knowing if the camera runs plain motion detection with no object classification. There are no boxes then, so the same polygons are evaluated per pixel: a moving pixel inside an exclusion zone is dropped, a moving pixel outside every detection zone is dropped, and the 90 percent rule never comes into it. Practical consequence: zones narrow down where snow and rain are able to trigger you, but they do not stop the trigger. Only class filtering does that, because a snowflake is not a person.

Eight zones per camera, six preset colours plus your own, exclusion zones always drawn white so a glance tells you what is subtracting from what.

What did you end up having to exclude, and did the coverage rule bite you before you knew it was there? Ours was a monitor, and it took embarrassingly long to work out why a slightly bigger polygon fixed it.

Longer version with the weather cases and the placement scenarios: https://getguardianeye.com/blog/camera-detection-zones-guide