I'm trying to calculate the bending radius of a product under cyclic bending using image processing with OpenCV and Python.
The image processing part is defined (the code is at [Red dot coordinates detection](https://stackoverflow.com/questions/61769416/red-dot-coordinates-detection) )

The code returns center coordinates of contours of specific size. I'm now trying to populate a 2D array of these coordinates so that I can use coordinates of two adjacent points to calculate the bending radius.

The problem is that the array population should be inside the for loop and that when I allocate the array beforehand, I don't know the size.

EDIT: bellow is the code from the link above with the FOR loop for filtering out the contours by area and displaying the center coordinates.

```
import cv2
import numpy as np
from matplotlib import pyplot as plt
import imutils

#load image
img = cv2.imread('dot4_red.jpg')

#apply median blur, 15 means it's smoothing image 15x15 pixels

blur = cv2.medianBlur(img,15)

#convert to hsv
hsv = cv2.cvtColor(blur, cv2.COLOR_BGR2HSV)

#color definition
red_lower = np.array([0,0,240])
red_upper = np.array([10,10,255])

#red color mask (sort of thresholding, actually segmentation)
mask = cv2.inRange(hsv, red_lower, red_upper)

#copy image for, .findContours distorts the source image
mask_copy = mask.copy()

#find contours
cnts = cv2.findContours(mask_copy,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

#extract contours from the list??
cnts = imutils.grab_contours(cnts)

#count number of conoturs of specific size
s1 = 500
s2 = 10000
array = [] #create empty array of no size

for cnt in cnts:
    area = cv2.contourArea(cnt)
    moment = cv2.moments(cnt)
    if s1<area<s2:
        print area
        c_x = int(moment["m10"]/moment["m00"])
        c_y = int(moment["m01"]/moment["m00"])
        print (c_x, c_y)

        array.append(c_x, c_y)

```