skytraq-datalog 0.1.1

Python driver for SkyTraq Venus GPS data loggers — download, decode and export datalog flash

skytraq-datalog

Python driver for SkyTraq Venus GPS data loggers (as used in the CanWay GPS app, circa 2012). Downloads the device's flash datalog over USB-serial and exports it as GPX.

Ported from reverse-engineered C# using the SkyTraq binary protocol.

Requirements

• Python 3.11+
• pyserial >= 3.5
• tqdm >= 4.60

Installation

pip install skytraq-datalog

This installs the skytraq-download command.

Usage

Command line

Either use as module with python -m skytraq or as tool skytraq-download

# Download all tracks, one GPX file per trip
skytraq-download /dev/ttyUSB0

# Custom file prefix
skytraq-download /dev/ttyUSB0 --prefix my_hike

# All trips in one file
skytraq-download /dev/ttyUSB0 --single --out all_tracks.gpx

# Custom initial baud rate (driver switches to 115200 automatically)
skytraq-download /dev/ttyUSB0 --baud 38400

# Adjust the gap that separates trips (default: 10 minutes)
skytraq-download /dev/ttyUSB0 --gap 5

By default each trip is written to a separate file named by its UTC start time: tracks_2024-03-01_09-15-00.gpx, tracks_2024-03-01_14-32-00.gpx, …

Python API

from skytraq.gps import SkytraqGPS
from skytraq.gpx import export_gpx, export_gpx_split

gps = SkytraqGPS("/dev/ttyUSB0")
points = gps.download_tracks()          # connects, downloads, reboots device

# One file per trip (split on >10 min gaps or device trip-start markers):
paths = export_gpx_split(points, "track")

# Or everything in one file:
export_gpx(points, "all_tracks.gpx")

How it works

1. Opens the serial port and commands the device to switch to 115200 baud.
2. Queries flash log metadata (sector count, time/distance/speed thresholds).
3. Downloads raw 4096-byte flash sectors in batches, verifying each with an XOR checksum.
4. Reboots the device so it returns to its default baud rate.
5. Decodes each sector entry: GPS week number + time-of-week → UTC, ECEF → LLA, speed.
6. Writes GPX 1.1 files with <trkpt>, <ele>, <time>, and <speed> elements.

Entry types decoded

Type	Size	Notes
FIX_FULL	18 B	Absolute position (ECEF) + absolute timestamp
FIX_HALF	8 B	Differential ECEF delta + delta TOW from previous entry
FIX_POI	18 B	Point-of-interest, same encoding as FIX_FULL
FIX_FULL_MULTI_HZ	20 B	High-frequency fix; direct LLA fixed-point + ms TOW
FIX_POI_MULTI_HZ	20 B	High-frequency POI
FIX_FULL_TRIP	—	FIX_FULL promoted to trip-start by a flag bit
FIX_FULL_TRIP_MULTI_HZ	—	FIX_FULL_MULTI_HZ promoted to trip-start

Known limitations

• GPS leap-second offset is hard-coded to 15 seconds (correct for data logged before 2017-01-01; add 1 second per subsequent leap second if needed).
• Altitude is ellipsoidal height (WGS-84). No EGM96 geoid correction is applied, so altitudes read roughly 10–50 m higher than mean sea level depending on location.

Project layout

src/
├── __main__.py    # CLI entry point (skytraq-download)
├── gps.py         # SkytraqGPS driver: serial I/O, packet framing, commands
├── decompress.py  # Flash sector decoder: entry parsing, coordinate conversion
├── gpx.py         # GPX 1.1 writer and trip splitter
└── types.py       # Dataclasses (LogPoint, LogInfo, LLA, ECEF) and enums

License

MIT