Unknow reference system for GPS data

[RamiNaim]

Good day!
I am trying out Ahmed's algorithm using example data from your repository and some other data from other sources. However, I cannot identify which spatial reference system is used in, for example, tracks in Athens example. Due to it, I cannot visualize it correctly.
I have also tried the algorithm on GPS data from Saint Petersburg, converted into UTM 35N reference system. But then I try to visualize resulted graph in the same reference system, it is hugely misplaced.
Could you please give me some insight on which SRID I should use in order to get valid road graph?

[hannes121]

I did not look into the algorithms, but for anyone like me who wants to use the data and needs the coordinate reference systems, it looks like they are:

crss = {
"berlin": "EPSG:32633", # WGS 84 / UTM zone 33N
"athen": "EPSG:2100", # GGRS87 / Greek Grid
"chicago": "EPSG:26716", # NAD27 / UTM zone 16N
}