RTK Positioning

Hardware

AutomatePro offers an optional RTK GNSS position sensor, giving it cm-level positional accuracy. This is based on the u-blox F9P and R series devices and includes positional accuracy down to 1 cm with RTCM corrections from a nearby base station. If the option is included, there will be a blue FAKRA connector for antenna connection. "GNSS-2" is used for position and "GNSS-1" is used for heading.

GNSS Position Specifications

Parameter	Value
Receiver	u-blox F9P or F9R (see Wheel Speed & Direction Input)
Connector	GNSS-2 (FAKRA C - Signal Blue)
Supported Constellation	GPS, Galileo, BeiDou, GLONASS
Positional Accuracy	Down to 1 cm 1. Using u-blox PointPerfect correction <6 cm
Max Navigation Update Rate	Default 1 Hz (can be configured up to 7 Hz, or 5 Hz as the moving base for heading)

Info

¹ Depends on antenna, distance to base station, or correction service. See the receiver datasheet for more information.

External Antenna

The AutomatePro system is compatible with a variety of multi-band high-precision GNSS antennas that have a FAKRA Type C connector (Signal Blue). More information on antennas used with AutomatePro is available here.

Wheel Speed & Direction Input

The AutomatePro provides options for both wheel speed and direction input for applications requiring dead reckoning.

Connection Details

Pin Name & Number	Function	Description
WHEEL TIC / PIN 51	Tachometer input	5-24VDC input range (with respect to the common GND)
WHEEL DIR / PIN 52	Wheel rotation direction input	5-24VDC input range (with respect to the common GND)

Connector

Development Breakout Board

Important

This is a non-standard option. Contact Lemvos for more information.

ROS API

Node: automatepro_gnss_position_node

Publishers

Topic	Type	Description
/sensor/gnss/position/fix	sensor_msgs/msg/NavSatFix	GNSS position data (navigation satellite fix).
/sensor/gnss/position/fix_velocity	geometry_msgs/msg/ TwistWithCovarianceStamped	Velocity in local ENU frame.
/sensor/gnss/position/monhw	ublox_msgs/msg/MonHW	Hardware status of the GNSS position module.
/sensor/gnss/position/monsys	ublox_msgs/msg/MonSYS	System monitor status of the GNSS position module.
/sensor/gnss/position/nmea	nmea_msgs/msg/Sentence	Raw NMEA messages.
/diagnostics	diagnostic_msgs/msg/ DiagnosticArray	GNSS position ROS driver diagnostics.

Subscribers

Topic	Type	Description
/sensor/gnss/correction	rtcm_msgs/msg/Message	RTCM or SPARTN Correction data

Parameters

Parameter	Type	Packaged default	Runtime R/W	Description
device	string	/dev/serial/by-id/usb-u-blox_AG_-_www.u-blox.com_u-blox_GNSS_receiver_F9P-if00	read	Serial port for the F9P receiver.
frame_id	string	gnss_position	read	Frame ID for published messages.
config_on_startup	bool	false	read	Leaves receiver flash configuration unchanged at startup.
gpio.chipname	string	gpiochip0	read	GPIO chip used for receiver reset recovery.
gpio.line_num	int	134	read	GPIO line used for receiver reset recovery.
gpio.reset_time_s	int	1	read	Reset pulse duration in seconds.
recovery.cycle_time_s	int	1	read	Base interval between recovery attempts in seconds; it doubles after each failed attempt up to recovery.backoff_max_s.
recovery.backoff_max_s	int	60	read	Longest interval between recovery attempts in seconds.
recovery.gpio_pulse_limit	int	3	read	Consecutive pulses of the shared reset line before this node stops pulsing. A pulse resets both receivers.
watchdog.timeout_ms	int	3000	read	Watchdog timeout in milliseconds.
watchdog.cycle_time_ms	int	500	read	Watchdog check interval in milliseconds.
publish.all	bool	false	read	Enables all publisher groups when true.
publish.aid.hui	bool	false	read	Enables AID-HUI message publishing.
publish.nav.posllh	bool	false	read	Enables NAV-POSLLH message publishing.
publish.nav.posecef	bool	false	read	Enables NAV-POSECEF message publishing.
publish.nav.relposned	bool	false	read	Keeps relative-position heading messages disabled for the position receiver.
publish.nmea	bool	true	read	Enables NMEA sentence publishing.
publish.mon.hw	bool	true	read	Enables UBX-MON-HW hardware status publishing.
publish.mon.sys	bool	true	read	Enables UBX-MON-SYS system status publishing.
debug	int	0	read	Debug verbosity; range 0-4.

Configuration

Driver: automatepro_gnss_driver Container: automatepro-core-driver

info

Runtime configuration files are in the /opt/automatepro/config/ros directory. Packaged defaults are installed in /opt/automatepro/defconfig/ros. The runtime files are mounted into the Docker container and used by the ROS driver. Environment variables can be set in the /opt/automatepro/.env file.

The runtime configuration file is:

/opt/automatepro/config/ros/gnss_position_params.yaml

The packaged default source is:

/opt/automatepro/defconfig/ros/gnss_position_params.yaml

ROS Configuration

# Configuration Settings for F9P device in Moving Base Mode
automatepro_gnss_position_node:
  ros__parameters:
    debug: 0                    # Range 0-4 (0 means no debug statements will print)

    device: /dev/serial/by-id/usb-u-blox_AG_-_www.u-blox.com_u-blox_GNSS_receiver_F9P-if00 #/dev/ttyACM1
    frame_id: gnss_position

    config_on_startup: false    # If false, the node will not override configurations of the device on startup
                                # Device should be configured with u-center and configurations should be saved in flash
                                # Please use the configuration file provided by Lemvos

    # GPIO configuration
    gpio:
      chipname: "gpiochip0"
      line_num: 134
      reset_time_s: 1

    # Recovery configuration
    recovery:
      cycle_time_s: 1
      backoff_max_s: 60
      gpio_pulse_limit: 3

    # Watchdog configuration
    watchdog:
      timeout_ms: 3000
      cycle_time_ms: 500

    # Enable u-blox gnss message publishers
    publish:
      all: false
      aid:
        hui: false
      nav:
        all: false
        posllh: false
        posecef: false
        relposned: false
      nmea: true
      mon:
        hw: true
        sys: true

Important

Restart the automatepro-core-driver Docker container after changing the configuration. Configuration changes are applied only after the container restarts.

sudo systemctl restart automatepro-core-driver

Device Configuration

This section describes the configuration of the GNSS device. To explore the capabilities of the GNSS device, refer to the u-blox documentation for more details.

Check the configuration section for more details.

Automatic Recovery

The driver watches the data stream from the receiver. It checks every watchdog.cycle_time_ms and starts recovery when no message has arrived for watchdog.timeout_ms.

Recovery runs in three steps, the least invasive first:

1. Reopen the serial connection, leaving the receiver untouched.
2. Reset the receiver in software with a UBX CFG-RST hot start, which keeps the battery-backed data so re-acquisition is fast.
3. Pulse the reset line to power-cycle the receiver.

Each step ends by reopening the connection. The driver waits recovery.cycle_time_s between attempts and doubles the wait after each failed attempt, up to recovery.backoff_max_s.

info

The reset line is shared, so a pulse resets the position and the heading receiver together. Each node stops pulsing after recovery.gpio_pulse_limit consecutive pulses, counting the other node's pulses as well, and resumes only once data arrives again.

Example

This example prints the latitude, longitude, and altitude by subscribing to the /sensor/gnss/position/fix topic. The tutorial package is available in the AutomatePro tutorials repository, and its README explains how to build and run the examples.

Python

Source: gnss_position.py

import rclpy
from rclpy.executors import ExternalShutdownException
from rclpy.node import Node
from sensor_msgs.msg import NavSatFix


class GNSSPositionSubscriber(Node):

    def __init__(self):
        super().__init__('gnss_position_subscriber')
        self.subscription = self.create_subscription(
            NavSatFix,
            '/sensor/gnss/position/fix',
            self.listener_callback,
            10)

    def listener_callback(self, msg):
        self.get_logger().info('Latitude: %f' % msg.latitude)
        self.get_logger().info('Longitude: %f' % msg.longitude)
        self.get_logger().info('Altitude: %f' % msg.altitude)


def main(args=None):
    rclpy.init(args=args)
    node = GNSSPositionSubscriber()
    try:
        rclpy.spin(node)
    except (KeyboardInterrupt, ExternalShutdownException):
        pass
    finally:
        node.destroy_node()
        rclpy.try_shutdown()


if __name__ == '__main__':
    main()

Run the node using the following command:

ros2 run automatepro_python_tutorials gnss_position_node

C++

Source: gnss_position.cpp

#include <rclcpp/rclcpp.hpp>
#include <sensor_msgs/msg/nav_sat_fix.hpp>

class GNSSPositionSubscriber : public rclcpp::Node
{
public:
  GNSSPositionSubscriber()
  : Node("gnss_position_subscriber")
  {
    subscription_ = this->create_subscription<sensor_msgs::msg::NavSatFix>(
      "/sensor/gnss/position/fix",
      10,
      std::bind(&GNSSPositionSubscriber::listener_callback, this, std::placeholders::_1));
  }

private:
  void listener_callback(const sensor_msgs::msg::NavSatFix::SharedPtr msg)
  {
    RCLCPP_INFO(this->get_logger(), "Latitude: %f", msg->latitude);
    RCLCPP_INFO(this->get_logger(), "Longitude: %f", msg->longitude);
    RCLCPP_INFO(this->get_logger(), "Altitude: %f", msg->altitude);
  }
  rclcpp::Subscription<sensor_msgs::msg::NavSatFix>::SharedPtr subscription_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  auto node = std::make_shared<GNSSPositionSubscriber>();
  rclcpp::spin(node);
  rclcpp::shutdown();
  return 0;
}

Run the node using the following command:

ros2 run automatepro_cpp_tutorials gnss_position_node