UM982 ROS Driver

This ROS driver reads data from a UM982 GPS device via a serial port and publishes it as ROS messages. It parses NMEA sentences (GGA and THS) to extract GPS position and heading information.

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Features

• Reads GPS position (latitude, longitude, altitude) from $GNGGA sentences.
• Reads heading from $GNTHS sentences.
• Publishes data as:
  • NavSatFix messages (/gps/fix topic).
  • Odometry messages (/gps/utmpos topic).
  • Float64 messages (/gps/heading topic).
• Configurable serial port and baud rate.

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Setup Instructions

1. Clone the Repository

Clone this repository into your ROS workspace:

cd ~/catkin_ws/src
git clone https://github.com/JorandG/UM982ROS
cd ~/catkin_ws
catkin_make
source devel/setup.bash

2. Add the Python Code

Ensure the provided Python script (um982ros.py) is located in the correct directory within your ROS workspace. For example:

~/catkin_ws/src/UM982ROS/um982ros.py

Make the script executable:

chmod +x ~/catkin_ws/src/UM982ROS/um982ros.py

3. Configure Parameters

The driver parameters can be set via the command line:

• Port: Serial port to which the UM982 is connected (default: /dev/ttyUM982).
• Baud Rate: Baud rate for the serial connection (default: 115200).

Run the driver directly:

rosrun um982_driver um982_driver.py _port:=/dev/ttyUSB0 _baud:=115200

4. Serial Port Permissions

Ensure your user has permission to access the serial port:

sudo usermod -a -G dialout $USER

Log out and back in for the changes to take effect.

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Topics

Published Topics

• /gps/fix (sensor_msgs/NavSatFix): GPS position (latitude, longitude, altitude).
• /gps/utmpos (nav_msgs/Odometry): UTM coordinates with heading.
• /gps/heading (std_msgs/Float64): Heading angle (in degrees).

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How It Works

1. NMEA Sentence Parsing

• $GNGGA:
  • Extracts latitude, longitude, and altitude.
  • Converts coordinates to decimal degrees.
• $GNTHS:
  • Extracts heading angle.

2. ROS Message Publishing

• Position and heading data are converted to ROS message formats and published on their respective topics.

3. Serial Communication

• Reads data from the UM982 device via the serial port.

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Using RTK with RTKLIB

To achieve Real-Time Kinematic (RTK) corrections for improved GPS accuracy, use the str2str tool from the RTKLIB suite. Follow these steps:

1. Install RTKLIB

Install RTKLIB on your Linux system:

sudo apt install rtklib

2. RTKLIB Command Explanation

Use the following str2str command to set up RTK corrections:

str2str -in ntrip://<username>:<password>@<ntrip_server>:<port>/<mountpoint> -out serial://<serial_port>:<baud_rate>:8:n:1

Command Parameters

• <username>: Your NTRIP service username.
• <password>: Your NTRIP service password.
• <ntrip_server>: The URL of the NTRIP caster (e.g., www.euref-ip.net).
• <port>: The port used by the NTRIP caster (e.g., 2101).
• <mountpoint>: The specific data stream mount point (e.g., M0SE00ITA0).
• <serial_port>: The serial port connected to the UM982 (e.g., /dev/ttyUSB0).
• <baud_rate>: The baud rate of the serial connection (e.g., 115200).

3. Example Command

Replace placeholders with actual values, except credentials:

str2str -in ntrip://username:password@www.euref-ip.net:2101/M0SE00ITA0 -out serial://ttyUSB0:115200:8:n:1

4. Notes

• Ensure the serial port name matches your device (e.g., /dev/ttyUSB0).
• Verify the mount point and network credentials with your NTRIP provider.

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Troubleshooting

1. No Data Published

• Verify the serial port and baud rate:

  ls /dev/tty*

• Check permissions for the serial port.

2. GPS Not Locked

• The GPS may take some time to lock onto satellite data, especially after a reset or in poor signal conditions.

3. Incorrect Data

• Verify NMEA sentences output by the UM982.
• Check for potential interference or hardware issues.