Analysis tools for road network managers require in many cases geometrical characteristics of the horizontal and vertical alignments to be known. However, in many cases, no databases are available or data are not sufficiently reliable to allow such analysis. This study presents the development of a tool, which allows determining horizontal and vertical alignments from continuous three dimensional GPS data measured on the centre-line of two-lane rural roads. Generation of straight lines, circles and parabolas from GPS data is not a simple task and has to be done by special constrained regression procedures in order to assure that the resulting elements are tangent to each other. Special procedures allow the user to do the analysis using default values or in a way as to follow more or less the oscillations of the measured GPS data. Performances of this tool were tested as well on fictive alignments as on real GPS databases provided by the ministry of transportation of the province of Quebec. Some useful applications of alignments generated by the algorithm are also presented.