GNSS Odometry ROS Package

This ROS package computes odometry heading for a robot using GNSS (Global Navigation Satellite System) data or wheel odometry data. It is designed to work with ROS Melodic and provides a modular and configurable implementation.

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Table of Contents

1. Overview
2. Features
3. Calculation
4. Dependencies
5. Installation
6. Usage
7. Parameters
8. Launch Files

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Overview

The gnss_odom package computes odometry for a robot using either:

• GNSS data: Computes heading and speed based on consecutive GNSS fixes.
• Wheel odometry data: Computes heading and speed based on displacement from wheel encoders.

The package publishes the computed odometry as an Odometry message, which can be used by other ROS nodes for navigation, localization, or mapping.

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Features

• Computes heading from GNSS fixes or odometry data.
• Uses least-squares fitting for a smoother heading estimate.
• Corrects heading direction based on velocity sign.
• Publishes odometry messages with orientation information.

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Calculation

The node supports two methods for heading calculation:

1. Direct GNSS Bearing

   • Uses pyproj.Geod.inv() to get the GNSS bearing.
   • Converts it to radians and applies an optional offset.

2. Least-Squares Line Fitting

   • Stores recent GNSS/odometry positions.
   • Fits a line using np.linalg.lstsq().
   • Computes the heading angle from the line slope.
   • Corrects direction based on movement and velocity.

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Dependencies

ROS Packages

• rospy
• sensor_msgs
• nav_msgs
• geometry_msgs

Python Libraries

• pyproj (for geodetic calculations)
• numpy (for basic mathematical operations)

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Installation

1. Clone the Repository:

   cd ~/catkin_ws/src
   git clone https://github.com/ikh-innovation/gnss_odom.git

2. Install Dependencies: Ensure that the required ROS packages are installed:

   sudo apt-get install ros-melodic-sensor-msgs ros-melodic-nav-msgs ros-melodic-geometry-msgs

   Install the pyproj Python library:

   pip install pyproj numpy

3. Build the Package:

   cd ~/catkin_ws
   catkin_make
   source devel/setup.bash

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Usage

Running the Node

To run the gnss_odom node, use the following command:

rosrun gnss_odom gnss_odom

Launch Files

The package includes launch files for easy configuration and execution. To use a launch file:

roslaunch gnss_odom gnss_odom.launch

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Parameters

The following parameters can be configured for the gnss_odom node:

Parameter Name	Description	Default Value
cmd_vel_topic	Command velocity topic	/aristos/wheel/cmd_vel
fix_topic	GNSS fix topic	/aristos/filter/positionlla/gnss
odom_topic	Odometry input topic	/aristos/odometry/gps/onlyRTK
odom_pub_topic	Published odometry topic	gnss_heading/odom
use_odometry	Use odometry instead of GNSS for heading	true
velocity_threshold	Minimum velocity for heading update	0.2 m/s
distance_threshold	Minimum distance for heading update	0.05 m
heading_offset	Additional heading offset (radians)	0.0
use_fitted_heading	Enable least-squares heading estimation	true
num_fit_points	Number of past points used for fitting	4
gnss_ellipsoid	Ellipsoid model used by pyproj	WGS84

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Published Topics

• gnss_heading/odom (nav_msgs/Odometry)
  Publishes computed odometry data with orientation.

Subscribed Topics

• /aristos/wheel/cmd_vel (geometry_msgs/Twist)
  Stores velocity data for heading correction.
• /aristos/filter/positionlla/gnss (sensor_msgs/NavSatFix)
  Processes GNSS data to compute heading.
• /aristos/odometry/gps/onlyRTK (nav_msgs/Odometry)
  Processes odometry data when enabled.

Launch Files

The package includes the following launch files:

gnss_odom.launch

Launches the gnss_odom node with default parameters. You can override parameters using the arg tag.

Example:

<launch>

  <node name="gnss_odom_node" pkg="gnss_odom" type="gnss_odom" output="screen">
    <param name="cmd_vel_topic" value="/aristos/wheel/cmd_vel" />
    <param name="fix_topic" value="/aristos/filter/positionlla/gnss" />
    <param name="odom_topic" value="/aristos/odometry/gps/onlyRTK"/>
    <param name="odom_pub_topic" value="gnss_heading/odom" />
    <param name="use_odometry" value="true"/>
    <param name="velocity_threshold" value="0.2"/>
    <param name="distance_threshold" value="0.05"/>
    <param name="heading_offset" value="0.0"/>
    <param name="use_fitted_heading" value="true"/>
    <param name="num_fit_points" value="4"/>
    <param name="gnss_ellipsoid" value="WGS84"/> <!--pyproj supported ellipsoids-->
  </node>

</launch>