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I want to apply homography to the following points:

array([[-7.4894, 1.8873],
 [-7.4973, 1.8543],
 [-7.5375, 1.6725],
 [-7.5681, 1.522 ],
 [-7.5961, 1.371 ],
 [-7.6252, 1.2013],
 [-7.6504, 1.031 ],
 [-7.667 , 0.8985],
 [-7.6817, 0.7657],
 [-7.6954, 0.613 ],
 [-7.7054, 0.4786],
 [-7.7124, 0.3452],
 [-7.7182, 0.1931],
 [-7.7215, 0.0866],
 [-7.7716, 0.0872],
 [-7.7715, 0.0929],
 [-7.7651, 0.2884],
 [-7.7587, 0.4269],
 [-7.7528, 0.5233],
 [-7.7418, 0.6616],
 [-7.7275, 0.8116],
 [-7.7048, 1.0032],
 [-7.6916, 1.0988],
 [-7.6686, 1.2478],
 [-7.6352, 1.4379],
 [-7.6091, 1.5741],
 [-7.5784, 1.7219],
 [-7.538 , 1.8995],
 [-7.4894, 1.8873]], dtype=float32)

My camera homography matrix is like this:

array([[ 3.9643041e-04, 6.5913662e-07, 3.1965813e-03],
 [ 7.4297395e-07, -3.9652368e-04, -4.4492882e-04],
 [-9.3076696e-06, -3.5773560e-06, 1.0000000e+00]], dtype=float32)

When I try to apply homography with cv2.perspectiveTransform i get the following error:

`cv2.error: OpenCV(4.0.0) C:projectsopencv-pythonopencvmodulescoresrcmatmul.cpp:2270: error: (-215:Assertion failed) scn + 1 == m.cols in function 'cv::perspectiveTransform'`

I suspect i need another dimension for each point. But I am not sure how to add this dimension with numpy.

What is the correct way to solve this problem and is there a way to determine the root cause? The error message does not make much sense to me.

Make sure the pts shape is (n, 1, 2) or (1,n,2):

 pts = np.float32(pts).reshape(-1,1,2)
 #pts = np.array([pts], np.float32)
 cv2.perspectiveTransform(pts, M)

For example:

pts = np.array([[1,2,],[3,4]], np.float32)
M = np.array([[ 3.9643041e-04, 6.5913662e-07, 3.1965813e-03],
 [ 7.4297395e-07, -3.9652368e-04, -4.4492882e-04],
 [-9.3076696e-06, -3.5773560e-06, 1.0000000e+00]], dtype=np.float32)

## (n, 1, 2)
pts1 = pts.reshape(-1,1,2).astype(np.float32)
dst1 = cv2.perspectiveTransform(pts1, M)

## (1, n, 2)
pts2 = np.array([pts], np.float32)
dst2 = cv2.perspectiveTransform(pts2, M)

Result:

>>> print(pts1)
[[[1. 2.]]

 [[3. 4.]]]
>>> print(dst1)
[[[ 0.00359439 -0.00123725]]

 [[ 0.00438869 -0.00202888]]]
>>> print(pts2)
[[[1. 2.]
 [3. 4.]]]
>>> print(dst2)
[[[ 0.00359439 -0.00123725]
 [ 0.00438869 -0.00202888]]]

Here is another example:

How do I use the relationships between Flann matches to determine a sensible homography?