b := struct.node.surface.xdir(sn,v)

Set the orientation of the surface system of node sn such that the \(x\)-direction is aligned with the projection of the surface vector v onto the normal plane, which is defined by the \(z\)-direction. This operation can only be performed upon nodes that have a valid surface system (to ensure that the \(z\)-direction always corresponds with the average normal direction of at least one of the shell-type SELs using the node). A return value of true indicates success and false indicates failure.


b - boolean flag: true indicates success, and false indicates failure


sn - structure node pointer

v - vector