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POfit an ellipse through points
 

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    <p>Using opencv for python I need to fit an ellipse (using cv2.fitEllipse) to the array of points returned by cv.FindCornerSubPix (here named 'features'). I have seen numerous examples of this on the internet, but I cannot figure it out. I figured cv.FindCornerSubPix returns an array of tuples, and my code triggered an error asking me for a numpy array as argument for cv2.fitEllipse, so I tried to convert 'features' to a numpy array and the error is now:</p> <p>'error: ......\src\opencv\modules\imgproc\src\contours.cpp:2019: error: (-215) points.checkVector(2) >= 0 &amp;&amp; (points.depth() == CV_32F || points.depth() == CV_32S)'</p> <p>on line 196 ('cv2.fitEllipse(ellipse)' at the end of my code), so I guess I am not feeding the right array format to cv2.fitEllipse. Would you please help me? The code below is just a modified version of the opencv sample lkdemo.py.</p> <pre><code> # search the good points features = cv.GoodFeaturesToTrack ( grey, eig, temp, MAX_COUNT, quality, min_distance, mask, 10, 0, 0.04) # refine the corner locations features = cv.FindCornerSubPix ( grey, features, (win_size, win_size), (-1, -1), (cv.CV_TERMCRIT_ITER | cv.CV_TERMCRIT_EPS, 20, 0.03)) elif features != []: # we have points, so display them # calculate the optical flow features, status, track_error = cv.CalcOpticalFlowPyrLK ( prev_grey, grey, prev_pyramid, pyramid, features, (win_size, win_size), 3, (cv.CV_TERMCRIT_ITER|cv.CV_TERMCRIT_EPS, 20, 0.03), flags) # set back the points we keep features = [ p for (st,p) in zip(status, features) if st] if add_remove_pt: # we have a point to add, so see if it is close to # another one. If yes, don't use it def ptptdist(p0, p1): dx = p0[0] - p1[0] dy = p0[1] - p1[1] return dx**2 + dy**2 if min([ ptptdist(pt, p) for p in features ]) &lt; 25: # too close add_remove_pt = 0 # draw the points as green circles for the_point in features: cv.Circle (image, (int(the_point[0]), int(the_point[1])), 3, (0, 255, 0, 0), -1, 8, 0) #Fit an ellipse array = np.array([tuple(i) for i in features]) ellipse = np.asarray(array) cv2.fitEllipse(ellipse) </code></pre>
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    1. USRaoul
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    1. COSolved it: #Fit an ellipse feature_matrix = cv.CreateMat(1, len(features), cv2.CV_32SC2) i = 0 for the_point in features: cv.Set2D(feature_matrix, 0, i, (int(the_point[0]), int(the_point[1]))) i = i + 1 if len(features) > 6: feature_matrix = np.asarray(feature_matrix) ellipse = cv2.fitEllipse(feature_matrix) image = np.asarray(image[:,:]) cv2.ellipse(image,ellipse,(0,255,0),2) image = cv.fromarray(image[:,:])
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      1. USRaoul
    2. COPlease post your comment as answer and accept it, that way anyone can see it's already solved. ;)
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      1. USjnovacho
 

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