SparkFunRTKExpress

This package is designed to work with the SparkFun RTK Express Kit. It provides a ROS2 Node that publishes NavSatFix messages, launch files to visualize the data using mapviz, and a UBX protocol implementation to communicate with the u-blox F9P GNSS module.

Features

• Direct communication with u-blox F9P GNSS module using UBX protocol
• ROS2 publisher for standard NavSatFix messages
• Configurable update rates up to 20Hz
• Mapviz integration for real-time position visualization
• Support for RTK corrections for high-precision positioning

Dependencies

• ROS2 (tested on Humble)
• Python 3.8+
• pyserial
• mapviz (for visualization)
• swri_transform_util (for coordinate transformations)

Setup Base and Rover

To configure your RTK base station and rover for centimeter-level positioning accuracy, please follow the SparkFun RTK Setup Guide. This guide provides step-by-step instructions for establishing proper communication between base station and rover.

For transmitting RTCM correction data between base and rover:

• You will need a way to transmit the RTCM correction data from the base to the rover
• Options include: computer with internet connection, serial point to point radio, XBee modules, etc.
• The SparkFun guide recommends using a 915MHz Serial Telemetry Radio kit
• For this implementation, we used the Holybro V3 3DR Radio 433 Telemetry 500mW 433MHz Data System (compatible with APM2.6 Pixhawk PX4 controllers)

Download Mapviz

For visualization of GPS data, you'll need to install Mapviz. Please follow the official Mapviz documentation for installation instructions. For additional usage information, the Robotics Knowledge Base guide provides helpful examples and configuration tips.

Hardware Setup and Configuration

Updating ESP32 Firmware

1. Download the Firmware Uploader

• Navigate to the SparkFun RTK Firmware Uploader GitHub Repo.
• Download the latest release for your operating system (Windows, Mac, or Linux).
• Extract or install it according to the instructions on the repo page.

2. Download the Latest Firmware Release

• Navigate to the SparkFun RTK Firmware Releases.
• Download the firmware .bin file (e.g., u-blox_F9P_SparkFun_RTK.x.x.x.bin) you - wish to flash onto your SparkFun RTK Express.

3. Flash the Firmware

• Power On the SparkFun
• Connect your board at a specific port labeled “ConfigESP32” with a USB-C cable
• Keep track of the location where you saved the .bin file
• Follow the instructions from Uploader Github Repo.

Updating u-blox GNSS Firmware

1. Download the Latest u-blox Firmware

• Go to the ZED-F9P Module Documentation
• Under "Firmware Update", select and download the firmware version you want

2. Install u-center and Update GNSS Firmware

• Download u-center (verify your u-blox chip model first)
• Connect your RTK Express to your computer
• Use u-center to flash the new firmware following the u-blox documentation

Configuring SparkFun RTK Express with u-center

1. Set Up u-center Connection

• Power on the SparkFun RTK Express
• Connect using the appropriate USB port
• Identify the COM port (Windows) or /dev/tty* device (Linux/macOS)

2. Configure Settings

• Check u-center's message windows to verify you're receiving GNSS data (NMEA or UBX messages)
• Use View > Messages View to modify specific settings (update rates, RTCM messages, power modes)
• To save settings permanently, go to View > Configuration View, select "Save to Flash and BBR"

Protocol Message

The ublox_protocol.py module in this package is based on the official UBX protocol specifications from u-blox:

1. Get the Interface Manual

• Go to the ZED-F9P Module Documentation
• Under "Interface Manual", select the manual corresponding to your firmware version
• This manual contains detailed information about all UBX protocol messages

2. Message Reference

• All messages implemented in this package follow the official UBX protocol specification
• When sending messages to the device, message structures and formats adhere to the interface manual
• The protocol module handles checksum calculation, message framing, and response parsing

Instalation

Installing Python Dependencies

chmod +x install_python_deps.sh
./install_python_deps.sh

Setup RTK Port

chmod +x setup_rtk.sh
./setup_rtk.sh

Building the Package

mkdir -p ~/sparkfun_ws/src
cd ~/sparkfun_ws/src

git clone https://github.com/pboon09/sparkfun_rtk_express.git

cd ~/sparkfun_ws
colcon build --symlink-install --packages-select sparkfun_rtk_express

source ~/sparkfun_ws/install/setup.bash

Usage

Basic Usage

To start the GPS publisher node:

ros2 run sparkfun_rtk_express gps_publisher.py --ros-args -p port:=/dev/ttyACM0

This will publish GNSS data to the /gps/fix topic as NavSatFix messages.

Parameters

The gps_publisher node supports the following parameters:

Parameter	Type	Default	Description
port	String	COM4	Serial port of the GPS device
baudrate	Integer	57600	Serial baudrate
frame_id	String	gps_link	TF frame ID for GPS measurements
rate_hz	Float	12.5	Publishing rate in Hz
high_rate	Boolean	True	Enable high-rate mode
measurement_rate_ms	Integer	80	GPS measurement rate in milliseconds

ros2 run sparkfun_rtk_express gps_publisher.py --ros-args \
  -p port:=/dev/ttyACM0 \
  -p baudrate:=115200 \
  -p rate_hz:=20.0 \
  -p measurement_rate_ms:=50

Using with MapViz

The package includes a launch file to start MapViz with a pre-configured setup for visualizing GPS data:

ros2 launch sparkfun_rtk_express mapviz_launch.launch.py

This will launch:

• MapViz with a map display and a NavSat display for GPS visualization
• Origin initialization for local coordinate frame
• Static transform publisher for the map frame

Feedback

If you have any feedback, please create an issue and I will answer your questions there.