AR fiducial markers are used for their convenience in finding the plane they lie on with regards to the camera. An AR marker usually has strong corners or other geometric features (for example, circles) that are clearly and quickly detectable. The 2D landmarks are arranged in a way that is pre-known to the detector, so we can easily establish 2D-3D point correspondence. The following are examples of AR fiducial markers:

In this example, there are several types of 2D landmarks. In the rectangular markers, these are the corners of the rectangles and the inner rectangles, while in the QR code ...