From the results obtained using the broadcast ephemeris (navigation file), you can analyze the accuracy level by comparing it to the coordinates of the precise final orbits file (.sp3), which can be downloaded via the following link: www.gnsscalendar.com
Precise ephemerides (final orbits) ensure high accuracy as it is postprocessed from data from various control centers. Thus, corrections are implemented that ensure the quality of satellite coordinates and satellite clock error.
Navigation messages, in turn, make it possible to determine the position of satellites in real time using time parameters, keplerian elements and disturbing parameters, which are obtained, for example, in RINEX (Receiver INdependent Exchange format).
Knowing the discrepancies in x, y, z, and the position (r) and speed (r ') of the satellite, it is possible to calculate (radial, along-track and cross-track) RAC orbits using the equations presented in the attached figures.
You can use the Keplerian elements. Please, see the chapter 2.1 of the Fortes thesis (Fortes, 2002) (https://www.ucalgary.ca/engo_webdocs/MEC/02.20158.LPFortes.pdf ).