In numerous theoretical considerations, as well as in navigational practical applications, there frequently occurs the necessity to evaluate the accuracy of linear objects on the basis of the accuracy of their particular points. A situation like that may occur, among other things, when the accuracy of the isobath, the quay edge or of the fairway are being evaluated. The directional error consti-tutes the proper measure for such evaluation. In the article presented formulae have been derived for the changę in decomposition parameters due to the rota-tion of coordinates as well as generał relationships of the directional error