Dear Kenneth,

My name is Ákos Halmai, I write the SL3Reader, we had an e-mail exchange a few years ago. You used the idea from it and I see this part in your code:

c = 1.4326
lim = 1.2

for i in range(1, len(self.df)):
t1 = self.df.loc[i, 'seconds']
v1 = self.df.loc[i, 'gps_speed']
d1 = math.tau - self.df.loc[i, 'gps_heading'] + (math.pi / 2)

Please, check the new version in my repo, the original idea was totally wrong! Now I wrote a correct one. The c does not account the curvature of the earth causing various issues outside Hungary. If you try the new approach, you should get a much better result.
In the next few days I going to polish it a little bit, but the idea is ready to use.

Best regards,
Ákos Halmai