System information (version)

• OpenCV => 4.x
• Operating System / Platform => any
• Compiler => Python 2.x/3.x

Detailed description

When OpenCV functions that processes point a sequence/point cloud is called from Python, it fails to process it because of unsupported shape of array. And so it needs reshape to pass through. If the output of point cloud processing functions is also a point cloud, it also needs to be reshaped in a similar way.

Steps to reproduce

pts = np.array([[10,5],[20,30],[70,20],[50,10]], np.int32)
pts = pts.reshape((-1,1,2))
cv2.polylines(img,[pts],True,(0,255,255))

...
pts = ...
rpts = pts.reshape((1,-1,2))
xfm_pts = cv2.perspectiveTransform(rpts,H).reshape((-1,2))

References

https://stackoverflow.com/questions/51723910/at-what-situation-points-need-to-be-reshaped-like-reshape-1-1-2-in-python-open/51724120

reported by @garybradski