fix charuco matchImagePoints

[AleksandrPanov]

The problem was in python bindings in void matchImagePoints(InputArrayOfArrays detectedCorners, InputArray detectedIds, OutputArray objPoints, OutputArray imgPoints).

detectedCorners may include aruco marker corners as vector<vector<Point2f>> or vector<Mat>. Any Mat in vector<Mat> must have 4 rows for 4 corners for one marker (one marker has 4 corners).

detectedCorners may include Charuco corners as vector<Point2f> or Mat. Python bindings add extra dimension to detectedCorners and therefore vector<Mat> case is additionally processed for charuco corners.

Until the PR merge, you can using custom matchImagePoints():

def matchImagePoints(charuco_board, charuco_corners, charuco_ids): objPoints = [] imgPoints = [] for i in range(0, len(charuco_ids)): index = charuco_ids[i] objPoints.append(charuco_board.getChessboardCorners()[index]) # objPoints[-1][0][1] = charuco_board.getRightBottomCorner()[1] - objPoints[-1][0][1] # set old axis direction imgPoints.append(charuco_corners[i]) return np.array(objPoints), np.array(imgPoints) 

Use sample from #23139 to see problem.

args:
-w=5 -h=7 -sl=0.04 -ml=0.02 -d=10 -v=choriginal.jpg

With fix:

detectedCorners includes charuco corners in this case. Python bindings add extra dimension to detectedCorners and therefore without fix detectedCorners processed as aruco marker corners and matchImagePoints returns bad values:

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[asmorkalov]

👍 Looks good!

[alalek]

From what other part of OpenCV code did you bring that design pattern?
Looks like we have malformed API design - InputArrayOfArrays is misused here.

/cc @vpisarev

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Accessing elements without type checks must be avoided.

[AleksandrPanov]

I fixed most of the issue (also updated docs, added cpp test). The issue of InputArrayOfArrays API design is discussed above in the conversation.