OpenCV, how to use arrays of points for smoothing and sampling contours?

Another possibility is to use the algorithm openFrameworks uses:

https://github.com/openframeworks/openFrameworks/blob/master/libs/openFrameworks/graphics/ofPolyline.cpp#L416-459

It traverses the contour and essentially applies a low-pass filter using the points around it. Should do exactly what you want with low overhead and (there's no reason to do a big filter on an image that's essentially just a contour).

Your Gaussian blurring doesn't work because you're blurring in column direction, but there is only one column. Using GaussianBlur() leads to a "feature not implemented" error in OpenCV when trying to copy the vector back to a cv::Mat (that's probably why you have this strange resize() in your code), but everything works fine using cv::blur(), no need to resize(). Try Size(0,41) for example. Using cv::BORDER_WRAP for the border issue doesn't seem to work either, but here is another thread of someone who found a workaround for that.

Oh... one more thing: you said that your contours are likely to be much smaller. Smoothing your contour that way will shrink it. The extreme case is k = size_of_contour, which results in a single point. So don't choose your k too big.

How about approxPolyDP()?

It uses this algorithm to 'smooth' a contour (basically gettig rid of most of the contour's points and leave the ones that represent a good approximation of your contour)