How to add callback to LineZone?

[AlainPilon]

Hi,

spent the afternoon playing with Supervision, it was very easy to build a toy demo but now that I am trying to add a "real" feature, I am at lost about how to interact with the LineZone object.

Basically, I need to be able to perform a callback (API call in my case) whenever an objet passes in or out of the line.

Python isnt my main language so I wouldnt date to write a PR but could we add a in_callback and out_callback lambda params to the LineZone class and have these called when the corresponding count is updated?

[SkalskiP]

Hi @AlainPilon 👋🏻 Sorry for the late response. I was AFK for the past few days. We have callbacks on our list of features with high priority. But it will probably take us 1-2 releases to get there.

For now, you'll need to write some custom code to enable that.

import supervision as sv

byte_tracker = sv.ByteTrack()
line_zone = sv.LineZone(start=LINE_START, end=LINE_END)

for frame in sv.get_video_frames_generator(source_path='source_video.mp4'):
    results = model(frame)[0]
    detections = sv.Detections.from_ultralytics(results)
    detections = byte_tracker.update_with_detections(detections)
    
    previous_in_count = line_zone.in_count
    previous_out_count = line_zone.out_count
    
    line_zone.trigger(detections)

    if previous_in_count != line_zone.in_count:
        in_callback()
    if previous_out_count != line_zone.out_count:
        out_callback()

Also, keep in mind that we are working on a new implementation of LineZone.

[AlainPilon]

Thanks. I couldnt wait to took it upon myself to hack something.

As stated about, Python is not my strength but I wrote this:

https://github.com/AlainPilon/better_line_counter/blob/main/line_counter.py

I saw that you have on your project board a story to refactor/improve the LineCounter so I will look out for it but until this, I think my solution is enough (for my requirements).

I think using dependency injections would be a great pattern for LineCounter as we could inject a TraficController (what to do on incoming/outgoing events) and a TriggerRule (to customize that should trigger the incoming/outgoing events, ex: partial line overlap) to make it easier to configure the LineCounter behaviour.

We are planing on using Supervision in an industrial setting so I am sure we will come up with more real life requirements!