Creating your own contour in opencv using python

Question

I have a set of boundary points of an object.

I want to draw it using opencv as contour.

I have no idea that how to convert my points to contour representation.

To the same contour representation which is obtained by following call

contours,_ = cv2.findContours(image,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE) 

Any ideas?

Thanks

Answer 1

By looking at the format of the contours I would think something like this should be sufficient:

contours = [numpy.array([[1,1],[10,50],[50,50]], dtype=numpy.int32) , numpy.array([[99,99],[99,60],[60,99]], dtype=numpy.int32)] 

This small program gives an running example:

import numpy import cv2  contours = [numpy.array([[1,1],[10,50],[50,50]], dtype=numpy.int32) , numpy.array([[99,99],[99,60],[60,99]], dtype=numpy.int32)]  drawing = numpy.zeros([100, 100],numpy.uint8) for cnt in contours:     cv2.drawContours(drawing,[cnt],0,(255,255,255),2)  cv2.imshow('output',drawing) cv2.waitKey(0) 

Answer 2

To create your own contour from a python list of points L

L=[[x1,y1],[x2,y2],[x3,y3],[x4,y4],[x5,y5],[x6,y6],[x7,y7],[x8,y8],[x9,y9],...[xn,yn]] 

Create a numpy array ctr from L, reshape it and force its type

ctr = numpy.array(L).reshape((-1,1,2)).astype(numpy.int32) 

ctr is our new countour, let's draw it on an existing image

cv2.drawContours(image,[ctr],0,(255,255,255),1)