This is guide on streaming GPS data from SparkFun GPS-RTK Dead Reckoning pHAT for Raspberry Pi (ZED-F9R) through ROS 2. Since ROS 2 does not officially Raspbian, I installed Ubuntu 20.04 on raspberry pi.
There is no official image for ubuntu 20.04 desktop for raspberry pi. However, you can install ubuntu 20.04 server and then install ubuntu-desktop sudo apt-get install ubuntu-desktop. [Update: It seems that Lubuntu Desktop is more stable operation on a raspberry pi, I used desktopify to install Lubuntu Desktop on my ubuntu server.]
This steps enables serial communication from the GPS module to ubuntu. I followed the guide here, but I listed them below for your convenience.
- Disable [email protected]
sudo systemctl stop [email protected]
sudo systemctl disable [email protected]
sudo systemctl mask [email protected]
- Setup udev rules, create a new file
/etc/udev/rules.d/10-local.rulesand write the following linse.
KERNEL=="ttyS0", SYMLINK+="serial0" GROUP="tty" MODE="0660"
KERNEL=="ttyAMA0", SYMLINK+="serial1" GROUP="tty" MODE="0660"
Reload udev rules: sudo udevadm control --reload-rules && sudo udevadm trigger
-
Add user to tty group:
sudo adduser ubuntu tty(assuming default ubuntu usernameubuntu, feel free to add your own username.) -
Delete substring
console=serial0,115200from/boot/firmware/cmdline.txt. There is a single line in this file, just remove the substring from the line. -
Restart
sudo reboot
When booting raspberrypi, do not plug in the pHAT module. Signals from UART will interrupt boot process. Plugin pHAT after the pi is booted.
When plugging in pHAT, tilted the pHAT so that the power pins are connected last. For some reason if the power pins are touched first, raspberrypi will reboot and cause the issue mentioned above.
TODO: disable UART temporarily during boot should solve this problem, will update once I manage to get it working.
Download sparkfun ublox package. (Requires Python3 and pip3, spidev.)
sudo pip3 install spidev
sudo pip3 install sparkfun-ublox-gps
The default package does not provide functions to parse GPS covariance matrix, but we can easily add our own.
In /usr/local/lib/Python3.x/dist-packages/ublox_gps,
after function geo_coords() on line 196, add another function that parse the covariance.
def geo_cov(self):
# Here we change the message type to COV
self.send_message(sp.NAV_CLS, self.nav_ms.get('COV'))
parse_tool = core.Parser([sp.NAV_CLS])
cls_name, msg_name, payload = parse_tool.receive_from(self.hard_port)
# There is no scaling factor so we can just return the payload
return payload
Details on ublox messages can be found here.
Follow the guide here to install ROS 2 Foxy.
cd [your_ros_ws]/src
git clone https://github.com/FrankBu0616/ros2_zed_f9r_gps.git
cd ..
colcon build
source install/setup.bash
To start publishing data, ros2 run zed_f9r_gps gps_publisher.