Скачать или смотреть How to Fix cv2.projectPoints() Error in OpenCV

Encountering an error using `cv2.projectPoints()` in OpenCV? This guide explains how to resolve the "Rotation must be represented by 1x3 or 3x1 vector" error, step-by-step.
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This video is based on the question https://stackoverflow.com/q/63631979/ asked by the user 'liad inon' ( https://stackoverflow.com/u/12657160/ ) and on the answer https://stackoverflow.com/a/63638299/ provided by the user 'unlut' ( https://stackoverflow.com/u/7602551/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting cv2.projectPoints() in OpenCV

OpenCV is an incredible library widely used in computer vision, but it doesn't come without its challenges. One common issue developers face is when they encounter an error while using the cv2.projectPoints() function. If you find yourself grappling with the error message regarding rotation representation, you are not alone. This post will guide you through understanding the error and how to effectively resolve it.

Understanding the Problem

When trying to project 3D points onto a 2D image plane using cv2.projectPoints(), you may run into an error like this:

[[See Video to Reveal this Text or Code Snippet]]

This error typically indicates that the rotation vector (rvecs) being passed to the function is not in the correct format.

Code Snippet Leading to the Error

Let’s look at an example to clarify the situation:

[[See Video to Reveal this Text or Code Snippet]]

In the above code, the problem lies in how we are unpacking the results from the cv2.solvePnP() function.

Solutions to the Error

To resolve the issue, you need to ensure that you are getting the correct return values from the cv2.solvePnP() function. Here’s how to do it:

Step 1: Update solvePnP Usage

You should modify your call to cv2.solvePnP() to properly capture its return values. The updated line should look like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Check the Shapes

Once you've changed the function call, it's crucial to check the shapes of your matrices using:

[[See Video to Reveal this Text or Code Snippet]]

Make sure that:

mtx is of shape (3, 3)

tvecs is either a (3, 1) or (1, 3) shaped vector

List of Expected Shapes:

Rotation vector (rvecs): Must be of shape (3, 1) or (1, 3).

Translation vector (tvecs): Must be of shape (3, 1) or (1, 3).

Step 3: Execute the Projection

After ensuring the return values from solvePnP() are correctly captured, you can safely call cv2.projectPoints() without encountering the earlier error.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Errors can certainly be a hassle while coding, especially in complex libraries like OpenCV. By understanding the expected input and output requirements and ensuring you use the library functions accurately, you can easily navigate these common pitfalls. The next time you find yourself facing a cv2.projectPoints() error, remember to check your solvePnP() return values. Happy coding!