How to develop a model to detect a point crossed a line?

# How to develop a system which detects if a object crosses a line. I am developing a system, basically which tells a object crossed a line. Do I need to get the camera calibration matrix ? Do I need to understand camera calibration or we can use annotation line points(using CVAT) to calculate the math ? If yes and mandatory, I will go on that path. Please advice. ### Camera calibration matrix is required(mandatory) for below use case? [![enter image description here][1]][1] ### I guess, No Camera Calibration matrix required, since camera is just looking from top view [![enter image description here][2]][2] ## My approach, 1. Draw lines using CVAT 2. Write a program using opencv which uses object bouding box center and trip line intersection to calculate the crossing. [![I draw lines using CVAT ][3]][3] ### My code - Now when to apply camera calibration ? and How to apply ? Is it required to apply? def where_it_is(line, cX, cY): A, B = line aX = A[0] aY = A[1] bX = B[0] bY = B[1] val = ((bX - aX) * (cY - aY) - (bY - aY) * (cX - aX)) thresh = 1e-9 if val >= thresh: return -1 elif val <= -thresh: return 1 else: return 0 [1]: https://i.stack.imgur.com/ghRJH.jpg [2]: https://i.stack.imgur.com/S3stH.jpg [3]: https://i.stack.imgur.com/CV7I9.jpg Please advise, what api and methods I need to use to calibrate the camera using opencv