You just need to create a Plane object that corresponds to the surface of your board. This is easy to do: it looks like your board is flat in the XY plane, right? That means you need a Plane with a normal of (0, 0, 1), with the Z axis pointing up. Then you pick a point on the plane, any point on the surface of your board, for instance (0, 0, 0) (assuming your board is at z == 0).

Pass both the point and the normal to the Plane constructor, et voilà!

Note that the chessboard sample also does what you’re asking for.