MBS GPS Navigation Package

HUSKY_GPS

Hardware Requirements

1. Un-manned ground vehicle (UGV)| Un-manned aerial vehicle (UAV)
2. Global positiong system (GPS) device
3. Inertial measurement unit (IMU)
4. Logitech controller
  • Recommended GPS: EMLID REACH RS2

Optional Hardware Requirements

- LiDAR
- Camera
  • Recommended LiDAR: OUSTER

Software Requirements

1. Ubuntu 18.04
2. ROS-melodic
3. MYBOTSHOP GPS package
    - Installation of dependencies

Disclaimer:

The provided MYBOTSHOP GPS package allows for point to point navigation utilizing GPS coordinates. It integrates the MoveBase package which in turn allows for collision avoidance. This package is currently designed for 2D planes with a planned expansion for 3D planes. Caution must be exercised when using the package around people and or in an un-constrained environment as any fault in sensors or misconfiguration may lead to an accident.

Configuration

In the provided package, several configuration have to be adjusted which are:

  • Localization
    • GPS localization config file
    • Odom localization config file
  • MoveBase
    • Base local planner params
    • Costmap common params
      • Global costmap params
      • Local costmap params
    • Movebase params

In-depth information is documented by the authors of the robot localization package.

GPS Localization Config

In this configuration file, we combine three sensor readings, which are the robots odom, imu, and the gps.

  • frequency: 20
    • The frequency depicts the rate at which the node publishes information.
  • two_d_mode: true
    • It tells to ignore the height readings from the incoming sensors as we are navigating in 2D.
  • publish_tf: true
    • Publishes a transform from the map frame to the odom frame
  • transform_time_offset: 2
    • Offsets the transform as some packages require transforms to be future off-set by a few seconds.

Setting the sequence of transforms for this localization node.

  • odom_frame: odom
  • base_link_frame: base_link
  • world_frame: map
  • map_frame: map

It is important to change the odom to the odom published by your robot.

  • odom0: /your_robot/odom
    • This is typically published by the robots controller
  • odom0_config: [false, false, false, false, false, false, true, false, false, false, false, false,false, false, false]
    • The boolean values are (X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za).
    • v is velocity and a is acceleration
  • odom0_differential: true
    • This indicates whether the odom velocity should be computed from the given x and y positions.
  • imu0: /imu/data
  • imu0_config: [false, false, false, false, false, true, false, false, false, false, false, true, true, false, false]
    • The boolean values are (X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za).
    • v is velocity and a is acceleration
  • imu0_differential: false
  • odom1: /odometry/gps
    • This is typically published by the navsat node. Ensure that the correct topic is used according to what you have assigned.
  • odom1_config: [true, true, false, false, false, false, false, false, false, false, false, false, false, false, false]
    • The boolean values are (X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za).
    • v is velocity and a is acceleration
  • odom1_differential: false

It is highly important to tune the process noises.

  • process_noise_covariance:
    • This determines on how much to trust the incoming data. Each line represents X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za. Values for these are assigned along the diagonals.
  • initial_estimate_covariance:
    • This determines on how much to trust the initial data. Each line represents X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za. Values for these are assigned along the diagonals.

For more information, the following repository by MethylDragon has a great explanatory guide.

Odom Localization Config

In this configuration file, we combine two sensor readings, which are the robots odom, and imu.

  • frequency: 20
    • The frequency depicts the rate at which the node publishes information.
  • two_d_mode: true
    • It tells to ignore the height readings from the incoming sensors as we are navigating in 2D.
  • publish_tf: true
    • Publishes a transform from the odom frame to the map frame
  • transform_time_offset: 1
    • Offsets the transform as some packages require transforms to be future off-set by a few seconds.

Setting the sequence of transforms for this localization node.

  • odom_frame: odom
  • base_link_frame: base_link
  • world_frame: odom

It is important to change the odom to the odom published by your robot.

  • odom0: /your_robot/odom
    • This is typically published by the robots controller
  • odom0_config: [false, false, false, false, false, false, true, false, false, false, false, false,false, false, false]
    • The boolean values are (X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za).
    • v is velocity and a is acceleration
  • odom0_differential: false
    • This indicates whether the odom velocity should be computed from the given x and y positions.
  • imu0: /imu/data
  • imu0_config: [false, false, false, false, false, true, false, false, false, false, false, true, true, false, false]
    • The boolean values are (X, Y, Z, roll, pitch, yaw, Xv, Yv, Zv, rollv, pitchv, yawv, Xa, Ya, Za).
    • v is velocity and a is acceleration
  • imu0_differential: false

MoveBase Local Planner

It is recommended to configure the move base planner to ensure correct movement. Several important ones are:

  • meter_scoring: true
    • When true distance is measured in meters.
  • yaw_goal_tolerance: 0.157
  • Tolerance in radians for movebase.
  • xy_goal_tolerance: 0.25
  • Tolerance in xy coordinates for movebase.
  • path_distance_bias: 0.35
  • Weighting factor of how close the robot should stay to the path.
  • goal_distance_bias: 1.0
  • Weighting factor of how close the robot should attempt to reach the goal.
  • heading_lookahead: 0.325
  • Tolerance of looking ahead for available space for turning.

For more information, the following MoveBase Wiki has a brief explanation.

Costmap Common Params

The costmap will be used to integrate and utilize your existing sensor for collision avoidance.Important parameters for this are:

  • footprint: [[-0.21, -0.165], [-0.21, 0.165], [0.21, 0.165], [0.21, -0.165]]
  • The footprint defines a square size for the robot. The robots mid point is taken as 0,0 and the the corner points are the distance from the mid point.
  • footprint_padding: 0.1
  • Safety-gap that inflates the original footprint.
  • obstacle_layer:
  • Sensors that are utilized for sensing. Typically, scan is used for LiDARs and the sort. Important is to change the sensor_frame to match the URDF and the topic to match the input message of the LiDAR.

For more information, the following Costmap Wiki has a brief explanation.

Global Costmap Params

The global costmap of movebase node, as the name states publishes the global costmap. It takes the map, provided by the map server as a static layer. An important point to note is that some warning messages may occur if the on board computer system do not compute the transforms fast enough. These warnings can be ignored.

Local Costmap Params

The local costmap of movebase node publishes the local costmap. It ypically requires the odom frame to operate. However, as we want to depend solely on our GPS, we utilize the map frame for the local costmap as well.

MoveBase Params

The movebase params are important for changing the planner frequency and controller frequency. Usually the default settings are sufficient.

  • recovery_behavior_enabled: true
  • It rotates the robot to recover from faulty planning failures or positioning, at times this is not desirable and may need to be turned off.