ArUco grid board generator
An ArUco grid is a rectangle of markers with an even gap. It is the target to use when you want the pose of a known object, and when part of the target may be hidden.
Open the generator with this board
The separation has to be exact
cv2.aruco.GridBoard takes one marker length and one separation, and assumes the gap is the same across and down. Many generators spread the markers to fill the page, which makes those two gaps different. The printed board then does not match the model, and every pose is wrong by an amount nothing reports.
This generator uses the numbers you type and never scales them. If the grid will not fit, it says so and splits the sheet rather than quietly shrinking the markers.
Any part of the board is enough
Every marker carries its own ID, so the detector knows where each one sits on the board. A handful of visible markers is enough to solve for the pose of the whole board, which is why a grid tolerates hands, shadows and edges better than a chessboard.
Keep the gap generous
A gap of about a fifth of the marker length works well. Too little and the black borders of neighbouring markers blur into one shape that the detector rejects. A separation of zero never works.