Precise ephemerides from IGS

Hi

I am trying to visualize the GPS satellites orbits. I have found the ephemerides data provided by IGS and downloaded one of the ultra rapid file (in SP3 format) to do some testing.

When I read the file, I have x,y,z and clock for 31 satellites with a sample interval of 15 min over 48h.

I just took the x,y,z coordinates of one satellite and plotted it ind 3D. Here the result:



So it's not what I expected (isn't the orbit supposed to be elliptical?).

I am a beginner in this field so I don't really understand where this result come from. I didn't find a lot of information about the informations contained by those SP3 files. For instance, what is the reference frame used (the only information in the file is that the coordinate system is IGS14 but I don't know what it actually means)

Moreover I didn't really understand what is the clock parameter and I don't know if it is relevent for what I want to do.

Here the link to the file I used : ftp://cddis.gsfc.nasa.gov/gnss/products/1939/igu19390_00.sp3.Z