Do contours returned by cv::findContours have a consistent orientation?

Question

I am using OpenCV\'s cv::findContours function to extract contours in a binary image, in particular, I\'m extracting a hierarchy of contours (using the CV_RETR_CCOMP

Answer 1

I believe step 1 and 4 of the Appendix I ( in the [Suzuki85] paper you referenced, "Topological Structural Analysis of Digitized Binary Images by Border Following" ) cover your question per the below:

(1) Select one of the following:
(a) If f _{i, j} = 1 and f _{i, j - 1} = 0, then decide that the pixel ( i, j ) is the border following starting point of an outer border, increment NBD, and ( i ₁, j ₁ ) + ( i, j - 1 ).
(b) ...

(2) Depending on the types of the newly found border and ...

(3) From the starting point ( i, j ), follow the detected border ...

(4) If f _{i, j} != 1, then LNBD = | f _{i, j} | and resume the raster scan from the pixel ( i, j + 1 ). The algorithm terminates when the scan reaches the lower right corner of the picture.