time_sync_utils

This repository contains utilities for handling and monitoring time-synchronized data in ROS 2. It consists of two main packages: nmea_gpsd for bridging GPS data and topic_monitor for validating message synchronization.

1. topic_monitor

The topic_monitor package is a diagnostic tool used to verify that various ROS 2 topics are active and that their timestamps are synchronized within a specified threshold. It reads a list of target topics from a configuration file, monitors them for 5 seconds, and reports a summary of message counts and synchronization offsets.

Nodes

• topic_monitor_node: The primary C++ node that subscribes to topics and performs timing analysis.

Parameters

• topics_file (string, default: config/topics.yaml): The path to the YAML file listing topics to monitor.
• relative_path (bool, default: true): If true, the node looks for the topics_file relative to the package's share directory.
• sync_threshold_warn_seconds (double, default: 0.1): The time difference (in seconds) between a topic's timestamp and the reference topic that triggers a warning.
• sync_threshold_error_seconds (double, default: 1.0): The time difference that triggers an error.

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2. nmea_gpsd

The nmea_gpsd package is a ROS 2 utility designed to bridge ROS-based NMEA data to the gpsd service. It provides nodes to convert standard ROS messages (like NavSatFix) into NMEA sentences and forward them to gpsd via various protocols.

Note: The serial and TCP implementations in this package are currently considered partially developed and may require further refinement for specific production environments.

Nodes

navsat_gpsd_serial

This node converts ROS sensor_msgs/msg/NavSatFix and geometry_msgs/msg/TwistWithCovarianceStamped messages into standard NMEA $GPGGA and $GPRMC sentences. These sentences are published to a ROS topic and optionally written to a serial port.

• Subscribed Topics:

• gnss_1/llh_position (sensor_msgs/msg/NavSatFix): Source of position and fix status.

• gnss_1/velocity (geometry_msgs/msg/TwistWithCovarianceStamped): Source of speed and course.

• Published Topics:

• nmea_constructed (nmea_msgs/msg/Sentence): The generated NMEA sentences.

• Parameters:

• serial_port (string, default: /dev/tnt1): The virtual or physical serial port to write NMEA sentences to.

• baud_rate (int, default: 9600): Baud rate for the serial port.

• nmea_talker_id (string, default: GP): The talker ID prefix (e.g., GP for GPS, GN for GLONASS).

• default_num_satellites (int, default: 4): Default satellite count used in GGA sentences.

• default_hdop (double, default: 1.5): Default Horizontal Dilution of Precision.

• default_geoid_separation (double, default: 0.0): Default geoidal separation in meters.

nmea_gpsd_socket

This node acts as a TCP server that listens for a connection from gpsd. Once connected, it forwards NMEA sentences from a ROS topic directly to the TCP client.

• Subscribed Topics:

• Defined by nmea_topic parameter (default: /nmea) (nmea_msgs/msg/Sentence).

• Parameters:

• gpsd_host (string, default: 0.0.0.0): The address the TCP server binds to.

• gpsd_port (int, default: 3001): The port gpsd will connect to.

• nmea_topic (string, default: /nmea): The ROS topic containing NMEA sentences to forward.

nmea_gpsd_udp

This node forwards NMEA data to gpsd via UDP. It can also synthesize $GPRMC sentences by combining raw NMEA GGA data with SBG-specific UTC time messages.

• Subscribed Topics:

• nmea_topic (default: /nmea): ROS topic for incoming NMEA sentences.

• utc_topic (default: /sbg/utc_time): ROS topic for sbg_driver/msg/SbgUtcTime used to generate RMC sentences.

• Parameters:

• gpsd_host (string, default: 127.0.0.1): The destination IP where gpsd is listening for UDP.

• gpsd_port (int, default: 3001): The destination UDP port.

License

Both packages are licensed under the Apache License 2.0.