CODEWITHSUNDEEP
pythonopencv
Mudyla
Mudyla

Reputation: 277

Problem with using cv2.pointPolygonTest() and cv2.polylines()

I am trying to draw a shape and then check whether the point is inside the shape or no. Thought using cv2.polylines() to draw it and cv2.pointPolygonTest() to test should work am getting an error which is not very informative.

Traceback (most recent call last):
  File "C:\Users\XXX\Desktop\Heatmap\cvtest.py", line 32, in <module>
    dist = cv2.pointPolygonTest(cv2.polylines(img,[pts],True,(0, 255 , 0), 2), (52,288), False)
cv2.error: OpenCV(4.1.0) C:\projects\opencv-python\opencv\modules\imgproc\src\geometry.cpp:103: error: (-215:Assertion failed) total >= 0 && (depth == CV_32S || depth == CV_32F) in function 'cv::pointPolygonTest'

I am guessing the shape created with cv2.polylines() is not a contour. What would be the correct way to do it then? My current code:

import cv2
import numpy as np

img = cv2.imread('image.png')

pts = np.array([[18,306],[50,268],[79,294],[165,328],[253,294],[281,268],[313,306],[281,334],[270,341],[251,351],[230,360],[200,368],[165,371],[130,368],[100,360],[79,351],[50,334],[35,323]], np.int32)
pts = pts.reshape((-1,1,2))

dist = cv2.pointPolygonTest(cv2.polylines(img,[pts],True,(0, 255 , 0), 2), (52,288), False)
#print(dist)

cv2.imshow('test', img)
cv2.waitKey()
cv2.destroyAllWindows()

Upvotes: 0

Views: 12636

Answers (1)

J.D.
J.D.

Reputation: 4561

polylines is not the right input, it is used to draw a shape (docs)
pointPolygonTest instead needs the contour as an input (docs)

dist = cv2.pointPolygonTest(pts, (52,288), False) will return 1.0, meaning inside the contour.

Note that you can perform a pointPolygonTest without an image. But if you want to draw the results, you can use this code as a starter:

    import cv2
    import numpy as np

    #create background
    img = np.zeros((400,400),dtype=np.uint8)
    # define shape
    pts = np.array([[18,306],[50,268],[79,294],[165,328],[253,294],[281,268],[313,306],[281,334],[270,341],[251,351],[230,360],[200,368],[165,371],[130,368],[100,360],[79,351],[50,334],[35,323]], np.int32)
    pts = pts.reshape((-1,1,2))
    # draw shape
    cv2.polylines(img,[pts],True,(255), 2)
    # draw point of interest
    cv2.circle(img,(52,288),1,(127),3)
    # perform pointPolygonTest
    dist = cv2.pointPolygonTest(pts, (52,288), False)
    print(dist)
    # show image
    cv2.imshow('test', img)
    cv2.waitKey()
    cv2.destroyAllWindows()

Result:

enter image description here

Upvotes: 6

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