serial_to_ros

ROS Noetic package for reading GPS and IMU data from serial ports and publishing as standard ROS messages. Supports bidirectional communication — receives sensor data from Arduino and sends SLAM odometry back.

Architecture

The package contains two independent nodes:

• serial_gps_node — reads binary GPS packets from serial, publishes sensor_msgs/NavSatFix and std_msgs/Float64MultiArray, and writes SLAM position back to Arduino.
• serial_imu_node — reads ASCII IMU data from serial, publishes sensor_msgs/Imu.

Serial Data Formats

GPS Node — Binary Protocol

GPS node uses a framed binary protocol with packed structs. The same serial port handles both receiving GPS data and sending SLAM data.

Frame structure:

[0xBB] [0xAA] [payload bytes...]

No length field or checksum — the payload size is determined by the struct type.

GPS Data (Arduino → ROS), 18 bytes payload

struct __attribute__((packed)) GPS_Data {
    uint32_t timestamp;   // microseconds
    int32_t  latitude;    // degrees × 1e7 (e.g. 221234567 = 22.1234567°)
    int32_t  longitude;   // degrees × 1e7 (e.g. 1201234567 = 120.1234567°)
    int32_t  altitude;    // millimeters (divide by 1000.0 for meters)
    uint8_t  GPSFixType;  // 0 = no fix
    uint8_t  RTKStatus;   // 0 = none, 1 = float, 2 = fixed
};

Field	Type	Unit	Conversion
timestamp	uint32_t	microseconds	—
latitude	int32_t	degrees × 10^7	value / 1e7 → degrees
longitude	int32_t	degrees × 10^7	value / 1e7 → degrees
altitude	int32_t	millimeters	value / 1000.0 → meters
GPSFixType	uint8_t	—	0 = no fix
RTKStatus	uint8_t	—	0 = none, 1 = float, 2 = fixed

SLAM Position (ROS → Arduino), 16 bytes payload

struct __attribute__((packed)) SLAM_position {
    uint32_t timestamp;   // microseconds (from ROS header stamp)
    float    x;
    float    y;
    float    z;
};

When the GPS node receives odometry messages (default topic: /Odometry), it packs the position into this struct and sends it over serial with the 0xBB 0xAA header.

GPS Published Topics

gps/fix (std_msgs/Float64MultiArray):

Index	Value
data[0]	timestamp (microseconds)
data[1]	latitude (degrees)
data[2]	longitude (degrees)
data[3]	altitude (meters)
data[4]	GPSFixType
data[5]	RTKStatus

gps/navsat_fix (sensor_msgs/NavSatFix):

• header.frame_id = gps_link
• latitude, longitude in degrees, altitude in meters
• RTK status mapping:
  • GPSFixType == 0 → STATUS_NO_FIX
  • RTKStatus == 2 (fixed) → STATUS_GBAS_FIX
  • RTKStatus == 1 (float) → STATUS_SBAS_FIX
  • otherwise → STATUS_FIX

IMU Node — ASCII Protocol

IMU node reads newline-terminated ASCII text, one sample per line:

timestamp ax ay az gx gy gz\n

Field	Unit	Notes
timestamp	—	Device timestamp (logged only, not used in ROS message)
ax ay az	g	Linear acceleration, multiplied by gravity param to get m/s²
gx gy gz	rad/s	Angular velocity, published directly

IMU Published Topic

imu/data_raw (sensor_msgs/Imu):

• header.frame_id = imu_link
• linear_acceleration = acceleration × gravity (m/s²)
• angular_velocity in rad/s
• orientation_covariance[0] = -1 (orientation not available)

Dependencies

• ROS Noetic
• roscpp
• sensor_msgs
• serial — ROS serial library

Install serial:

sudo apt-get install ros-noetic-serial

Build

cd <workspace>
catkin build
source devel/setup.bash

Configuration

GPS Node — config/serial_gps.yaml

serial:
  port: "/dev/ttyUSB0"
  baud_rate: 115200
  timeout_ms: 1000

gps:
  frame_id: "gps_link"
  topic: "gps/fix"

slam:
  odom_topic: "/Odometry"

Parameter	Description	Default
serial/port	Serial port path	/dev/ttyACM0
serial/baud_rate	Baud rate	115200
serial/timeout_ms	Read timeout (ms)	1000
gps/frame_id	TF frame ID	gps_link
gps/topic	Float64MultiArray topic	gps/fix
gps/navsat_topic	NavSatFix topic	gps/navsat_fix
slam/odom_topic	Odometry subscription topic	/odom

IMU Node — config/serial_imu.yaml

serial:
  port: "/dev/ttyACM0"
  baud_rate: 115200
  timeout_ms: 1000

imu:
  frame_id: "imu_link"
  topic: "imu/data_raw"
  gravity: 9.81

Parameter	Description	Default
serial/port	Serial port path	/dev/ttyACM0
serial/baud_rate	Baud rate	115200
serial/timeout_ms	Read timeout (ms)	1000
imu/frame_id	TF frame ID	imu_link
imu/topic	Published topic name	imu/data_raw
imu/gravity	Gravity constant (g → m/s²)	9.81

Usage

Launch GPS node:

roslaunch serial_to_ros serial_gps.launch

Launch IMU node:

roslaunch serial_to_ros serial_imu.launch

Verify output:

rostopic echo /gps/navsat_fix
rostopic echo /gps/fix
rostopic echo /imu/data_raw

Arduino Reference

The repository includes main.cpp as an Arduino-side reference implementation. It demonstrates:

• GPS data transmission at 5 Hz via Serial1 (binary protocol)
• SLAM position reception via Serial1 (binary protocol)
• Debug output at 10 Hz via Serial (USB, ASCII)