During the autumn course 2007-2008 I was carring out the enterprise practices and the final project in “Centre Tecnològic per a la industria Aeronàutica i de l’Espai” (CTAE). The opportunity to work on CTAE cames up from the need of find a trainee engineer to develop a post-process GPS navigator using Matlab that may be a prototype of a real-time one implemented within a GPS software receiver. Recently, I just had studied RADARTEL and MATLAB, so I had fresh concepts about and they decide to trust in me to do it. On the other hand, CTAE had contacts with Dagoberto Salazar, UPC teacher and gAGE (research group in Astronomy and GEomatics) member, who has experience programming GPS navigation software in C++. This plus the specifications of the project – individual work, extention, idiom and combination of theory and practise – created the ideal framework to propose it as my final project degree. The GPS navigator should be able to calculate positioning from the data contained within RINEX data files.RINEX. RINEX (Receiver Independent EXchange format), is a standard that defines a format to save measurements made by a GPS receiver. The big advantage of RINEX is that unificating the format; it allows us to post-process data from any receiver, avoiding problems due to different brands incompatibilities. According to the working plan (attached) of CTAE, the creation of the GPS navigator has to be carried out through to stages. The first one is developing a RINEX reader able to read and save all data into a defined structure. And the second one is the implementation of the navigator over the data structure provided by the RINEX reader. Therefore, this document gathers the background or the needed knowledge to understand and create a software GPS navigator. The body of this report is arranged in three main chapters. The first one sets the theoric bases, where the navigator will be built. It is a key section that is used as a guide or a manual during the implementation. The second chapter is a high-level description of the RINEX reader and navigator’s structure, as well as a description of the most important algorithms through diagramflows. Finally, the third chapter is focused on analyse the results and propose some improvements or next steps which could be done in a following project.