Locating co-planar points to chessboard

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Hi,

I have been using the solvePnP function to get the translation and rotation between the camera and the chessboard. So fa I have manage to do this because I know the size of the chessboard. I was wandering if there could be a way of doing this in which the image corner location could be use to get the 3D location, and if so if it was possible to get the 3D position of other none corner features co-planar to the chessboard.

Any pointers would be appreciated.

Cheers