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How to find distance between centers of two green boxes?

asked 2017-06-03 06:37:07 -0500

New_H gravatar image

Hi , I am still beginner in opencv and I have this task :

find the distance between the centers of two green boxes using camera.

I could be able to find the centers of the boxes but how to find the distance between their centers ?

below is my code

really appreciate your help.

Many thanks.

import numpy as np
import cv2
import imutils


cap = cv2.VideoCapture(1)

while(1):

    #read frame and convert the color scheme of the frame BGR to HSV
    _, image = cap.read()
    image = imutils.resize(image, width=600)


    hsv = cv2.cvtColor(image, cv2.COLOR_BGR2HSV)

    #Our operations on the frame come here

    lower_pink = np.array([38, 50, 50])
    upper_pink = np.array([75, 255, 255])

    #Our frame, the HSV image, is thresholded among upper and lower pixel ranges to get only green colors

    mask = cv2.inRange(hsv, lower_pink, upper_pink)
    kernel = np.ones((5,5),'int')
    dilated = cv2.dilate(mask,kernel)

    res = cv2.bitwise_and(image,image, mask=mask)

    # Then we thresholded the masked image and get the contours.


    ret,thresh = cv2.threshold(cv2.cvtColor(res,cv2.COLOR_BGR2GRAY),3,255,cv2.THRESH_BINARY)


    # find contours in the thresholded image
    cnts = cv2.findContours(mask.copy(), cv2.RETR_EXTERNAL,
            cv2.CHAIN_APPROX_SIMPLE)
    cnts = cnts[0] if imutils.is_cv2() else cnts[1]


    # loop over the contours
    for c in cnts:
            # compute the center of the contour
            area=cv2.contourArea(c)
            M = cv2.moments(c)
            if M["m00"] >1000:
                cX = int(M["m10"] / M["m00"])
                cY = int(M["m01"] / M["m00"])

                # draw the contour and center of the shape on the image
                cv2.drawContours(mask, [c], -1, (0, 255, 0), 2)
                cv2.circle(mask, (cX, cY), 7, (0, 255, 255), -1)
                cv2.putText(mask, "center", (cX - 20, cY - 20),
                        cv2.FONT_HERSHEY_SIMPLEX, 0.5, (0, 255, 255), 2)



    cv2.imshow('frame',mask)

    k = cv2.waitKey(5) & 0xFF
    if k == 27:
        break

cap.release()
cv2.destroyAllWindows()
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Comments

you mean distance in pixels?

electron gravatar imageelectron ( 2017-06-03 06:56:54 -0500 )edit

in cm or inches .. even in pixels is ok ..

New_H gravatar imageNew_H ( 2017-06-03 07:00:00 -0500 )edit

2 answers

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answered 2017-06-03 07:09:34 -0500

electron gravatar image

updated 2017-06-03 07:11:36 -0500

For example, cX1 and cY1 are coordinates of center of first box, cX2 and cY2 are coordinates of center of second box. You can find the distance:

 distance = (((cX1 - cX2) ** 2) + ((cY1 - cY2) ** 2)) ** 0.5

If you know real sizes of boxes you can also compute distance in cm. But accuracy will be low.

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Comments

but how can I get cX1,cX2 and cY1,cY2 ?

New_H gravatar imageNew_H ( 2017-06-03 07:43:54 -0500 )edit

using your code. you wrote that you can find centers of boxes and seems that your code really can do this, just save coordinates cX, cY to appropiated variables

electron gravatar imageelectron ( 2017-06-03 08:24:09 -0500 )edit

Thank you so much

New_H gravatar imageNew_H ( 2017-06-03 11:59:24 -0500 )edit

but why the distance is changing when I move my cam forward or backward ?

New_H gravatar imageNew_H ( 2017-06-03 12:09:00 -0500 )edit

because cm count per pixel is different in these cases. distance in cm is the same, but in pixels it will change depends on your camera position. that's normal

electron gravatar imageelectron ( 2017-06-03 13:05:27 -0500 )edit
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answered 2017-06-03 07:23:01 -0500

Fynjy8 gravatar image

updated 2017-06-03 07:46:43 -0500

If, for example, box1.center = X1,Y1 and box2.center = X2,Y2 , then your answer is:

sqrt((X2-X1)^2 + (Y2-Y1)^2)

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Thanks a lot for your help :)

New_H gravatar imageNew_H ( 2017-06-03 07:43:19 -0500 )edit
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Asked: 2017-06-03 06:37:07 -0500

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Last updated: Jun 03 '17