Hi, I want to write program which detect the object and speed. I have problem with speed detection, values are weird Maybe someone wrote a similar program somewhen and can help me?

Python code program:

import dataclasses as dc
import math
import sys
import time
import numpy as np
import cv2
from PyQt5.QtWidgets import QApplication
@dc.dataclass(unsafe_hash=True)
class Coordinates:
    x: float
    y: float
def nothing(x):
#blueLower = (38, 86, 0)
cap = cv2.VideoCapture(2, cv2.CAP_DSHOW)
initial_time = time.time()
cv2.namedWindow("Tracking")
cv2.createTrackbar("LH", "Tracking", 0,360, nothing)
cv2.createTrackbar("LS", "Tracking", 0,255, nothing)
cv2.createTrackbar("LV", "Tracking", 0,255, nothing)
cv2.createTrackbar("UH", "Tracking", 255,255, nothing)
cv2.createTrackbar("US", "Tracking", 255,255, nothing)
cv2.createTrackbar("UV", "Tracking", 255,255, nothing)
object_detector = cv2.createBackgroundSubtractorMOG2(history=50, varThreshold=10)
app = QApplication(sys.argv)
screen = app.screens()[0]
dpi = screen.physicalDotsPerInch()
fps = round(cap.get(cv2.CAP_PROP_FPS))
coordinates = []
def convert_pixel_to_meter(pixels):
    return (pixels * 0.0254) / dpi
def convert_pixel_to_mm(pixels):
    return (pixels * 25.4) / dpi
def calculate_distance_between_point(x1, y1, x2, y2):
    return abs(math.sqrt(pow((x2 - x1), 2) + pow((y2 - y1), 2)))
while True:
    ret, frame = cap.read()
    height, width, _ = frame.shape
    roi = frame
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    l_h = cv2.getTrackbarPos("LH", "Tracking")
    l_s = cv2.getTrackbarPos("LH", "Tracking")
    l_v = cv2.getTrackbarPos("LH", "Tracking")
    u_h = cv2.getTrackbarPos("UH", "Tracking")
    u_s = cv2.getTrackbarPos("UH", "Tracking")
    u_v = cv2.getTrackbarPos("UH", "Tracking")
    blueLower = np.array([l_h, l_s, l_v])
    blueUpper = np.array([u_h, u_s, u_v])
    mask = cv2.inRange(hsv, blueLower, blueUpper)
    res = cv2.bitwise_and(frame, frame, mask=mask)
    contours, _ = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
    for cnt in contours:
        x, y, w, h = cv2.boundingRect(cnt)
        if w >50 and h > 50:
            cx = int((x+x+w)/2)
            cy = int((y+y+h)/2)
            cv2.rectangle(roi, (x, y), (x+w, y+h), (0, 255, 0), 3)
            cv2.circle(roi, (cx, cy), 5, (0, 0, 255), -1)
            text = "cx: " + str(cx) + ", cy: " + str(cy)
            cv2.putText(roi, text, (cx - 10, cy- 10), cv2.FONT_HERSHEY_SIMPLEX, 0.5, (0,255, 0), 2)
            print("Position: ", convert_pixel_to_mm(cx), convert_pixel_to_mm(cy))
            coordinates.append(Coordinates(convert_pixel_to_meter(x), convert_pixel_to_meter(y)))
            if len(coordinates) > 1:
                pixel_dimension = calculate_distance_between_point(coordinates[len(coordinates)-1].x,
                                                                   coordinates[len(coordinates)-1].y, x, y)
                distance_in_meter = convert_pixel_to_meter(pixel_dimension)
                speed = distance_in_meter / (time.time() - initial_time)
                print("AverageSpeed: ", speed)
    cv2.imshow("roi", roi)
    #cv2.imshow("Frame", frame)
    cv2.imshow("Mask", mask)
    cv2.imshow("res", res)
    key = cv2.waitKey(30)
    if key == 27:
        break
cap.release()
cv2.destroyAllWindows()
that’s all you said about this. can’t work with that.
don’t wait for someone to pull your teeth before you start talking. this isn’t gitmo, this is a website. I only use pliers in person.
best to spare the words and use pictures and other numbers instead.
please explain the(assumed !) relation between your qt-app’s screensize/dpi and measurement in the real world
please also read this and this
              
Program detect and tracking the object, shows object center position and calculates avarage speed by frames, I mean distance is counted beetween previous frame and next frame and then is divisible by time (previous frame and next frame). And I also tried convert pixel to meter. It looks like that:

screen630×880 246 KB
              
I read about calibration and pinhole camera. I have program to calibration camera, but I dont know how to load these parameters to my algorythm
I converted pixels to millimeter from position of object center. I meaused camera image width, I divided it into resolution and then I multiplied by the coordinates of the center.

I don`t know why I used dpi to convert, but yes, its don’t have relation I guess
mm_to_pix = 300.0/640
cx_mm = cx*mm_to_pix
cy_mm = cy*mm_to_pix
Now I have to solve problem with speed