Suggestion: Real world object size estimate instead of bounding box size

[R5fan]

Frigate currently gives the size of the bounding box and you can use that as a filter. That may be enough sometimes, but a cat or robotic mower or toy car close to the camera could be much "larger" than human or a real car further from the camara.

I think we can do better with just a little geometry. If you know the horizon line and the height of the camera, you can calculate (or at least guestimate) the distance of an object to the camera based on where the bottom of the object bounding box is in the frame, -assuming the object is on the ground and the world is flat. If you have a distance, you can correct the bounding box size to get a real world size estimate.

Of course, I wouldnt expect this to be super accurate for a million reasons, but it would be a lot better than just filtering on bounding box size. If you want to go full nerd, you could try to draw a perspective plane and take in to account camera FoV and lens distortion. I suspect there are apps/libraries that do just that for various purposes.

Edit: fspy would do just that: https://fspy.io/
Frigate users could use that to determine the properties of their cameras.