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.

QoS Configuration

Each topic in the topics.yaml file can optionally specify custom QoS (Quality of Service) settings. If not specified, default values are used.

Available QoS Options:

• history_depth (integer, default: 10): The depth of the message history queue.
• reliability (string, default: "reliable"): The reliability policy. Options:
  • "reliable": Ensures message delivery (may retry)
  • "best_effort": Does not guarantee message delivery
• durability (string, default: "volatile"): The durability policy. Options:
  • "volatile": Only subscribers that are alive at publication time receive messages
  • "transient_local": Late-joining subscribers may receive previously published messages

Example:

topics:
  - name: /example_topic
    type: sensor_msgs/msg/NavSatFix
    qos:
      history_depth: 5
      reliability: best_effort
      durability: transient_local

---

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.