Adds support automatic timestamp offset calculation.

calc_gps_map_csv.py

@@ -141,7 +141,7 @@ if __name__ == "__main__":
             df["datetime"] = pd.to_datetime(df["datetime"]) + pd.Timedelta(minutes=args.time_offset)
     elif args.auto_offset:
         gps_first = datetime.strptime(df["datetime"].iloc[0], "%Y-%m-%d %H:%M:%S.%f")
-        pcap_first = datetime.strptime(transmission_df["datetime"].iloc[0], "%Y-%m-%d %H:%M:%S.%f")
+        pcap_first = datetime.strptime(pd.to_datetime(transmission_df.first_valid_index()), "%Y-%m-%d %H:%M:%S.%f")
         calc_offset = gps_first - pcap_first
         if gps_first > pcap_first:
             time_offset = gps_first - pcap_first