PX4 User Guide
  • Introduction
  • Getting Started
    • Basic Concepts
    • Vehicles/Frames
    • Flight Controllers
    • Sensors
    • Radio Systems
    • Flight Modes
    • Vehicle Status Notifications
      • LED Meanings
      • Tune/Sound Meanings
      • Preflight Checks
    • Payloads & Cameras
    • Flight Reporting
  • Basic Assembly
    • Mounting the Flight Controller
    • Mounting the GPS/Compass
    • Vibration Isolation
    • Cable Wiring
    • CUAV Pixhawk V6X Wiring QuickStart
    • CUAV V5+ Wiring Quickstart
    • CUAV V5 nano Wiring Quickstart
    • Holybro Pixhawk 6C Wiring Quickstart
    • Holybro Pixhawk 6X Wiring Quickstart
    • Holybro Pixhawk 5X Wiring Quickstart
    • Holybro Pixhawk 4 Wiring Quickstart - Discontinued
    • Holybro Pixhawk 4 Mini Wiring Quickstart - Discontinued
    • Holybro Durandal Wiring Quickstart
    • Holybro Pix32 v5 Wiring Quickstart
    • Cube Wiring Quickstart
    • Pixracer Wiring Quickstart
    • mRo (3DR) Pixhawk Wiring Quickstart
  • Standard Configuration
    • Firmware
    • Airframe
    • Sensor Orientation
    • Compass
    • Gyroscope
    • Accelerometer
    • Airspeed
    • Level Horizon Calibration
    • Radio Setup
    • Joystick Setup
    • Flight Modes
    • Battery
    • Safety
      • Failsafe Simulation
    • ESC Calibration
    • Actuators
    • Autotune
  • Vehicle Types & Setup
    • Multicopters
      • Multicopter Config/Tuning
        • MC Filter/Control Latency Tuning
        • MC PID Tuning (Manual/Basic)
        • MC PID Tuning Guide (Manual/Advanced)
        • MC Setpoint Tuning (Trajectory Generator)
          • MC Jerk-limited Type Trajectory
        • Multicopter Racer Setup
      • X500 v2 (Pixhawk 6C)
      • X500 v2 (Pixhawk 5X)
      • X500 (Pixhawk 4)
      • S500 V2 (Pixhawk 4)
      • DJI F450 (CUAV v5+)
      • DJI F450 (CUAV v5 nano)
      • QAV250 (Pixhawk4 Mini) - Discontinued
      • DJI F450 + RTK (Pixhawk 3 Pro)
      • QAV250 (Pixhawk Mini)
      • QAV-R 5" Racer (Pixracer)
      • Omnicopter
    • Planes
      • Fixed Wing Config/Tuning
        • Fixedwing PID Tuning Guide
        • Fixedwing Advanced Tuning Guide
        • Fixedwing Trimming Guide
      • Reptile Dragon 2 (ARK6X)
      • Turbo Timber Evolution (Pixhawk 4 Mini)
      • Wing Wing Z84 (Pixracer)
    • VTOL
      • VTOL Config/Tuning
        • QuadPlane Configuration
        • Back-transition Tuning
        • VTOL w/o Airspeed Sensor
        • VTOL Weather Vane
      • Standard VTOL
        • FunCub QuadPlane (Pixhawk)
        • Ranger QuadPlane (Pixhawk)
        • Falcon Vertigo QuadPlane (Dropix)
      • Tailsitter VTOL
        • Build: TBS Caipiroshka Tailsitter Build (Pixracer)
      • Tiltrotor VTOL
        • Build: Convergence Tiltrotor (Pixfalcon)
    • Airships (experimental)
    • Autogyros (experimental)
      • ThunderFly Auto-G2 (Holybro pix32)
    • Balloons (experimental)
    • Helicopter (experimental)
      • Helicopter Config/Tuning
    • Rovers (experimental)
      • Traxxas Stampede
    • Submarines (experimental)
      • BlueROV2
    • Airframes Reference
  • Flying
    • First Flight Guidelines
    • Flying 101
    • Missions
      • Package Delivery Mission
    • GeoFence
    • Safety Point Planning
    • Flight Modes
      • Position Mode (MC)
      • Altitude Mode (MC)
      • Manual/Stabilized Mode (MC)
      • Acro Mode (MC)
      • Orbit Mode (MC)
      • Position Mode (FW)
      • Altitude Mode (FW)
      • Stabilized Mode (FW)
      • Acro Mode (FW)
      • Manual Mode (FW)
      • Takeoff Mode
      • Land Mode
      • Return Mode
      • Hold Mode
      • Mission Mode
      • Follow Me Mode
      • Offboard Mode
    • Terrain Following/Holding
  • Flight Log Analysis
    • Log Analysis using Flight Review
    • Log Analysis using PlotJuggler
  • Advanced Configuration
    • Finding/Updating Parameters
    • Full Parameter Reference
    • ECL/EKF Overview & Tuning
    • Flight Termination Configuration
    • Bootloader Flashing onto Betaflight Systems
    • Land Detector Configuration
    • Prearm/Arm/Disarm Configuration
    • IMU Factory Calibration
    • Sensor Thermal Compensation
    • Compass Power Compensation
    • Advanced Controller Orientation
    • Static Pressure Buildup
    • Serial Port Configuration
    • MAVLink Telemetry (OSD/GCS)
    • PX4 Ethernet Setup
    • Bootloader Update
  • Hardware (Drones&Parts)
    • Complete Vehicles
      • ModalAI Starling
      • PX4 Vision Kit
      • MindRacer BNF & RTF
        • MindRacer 210
        • NanoMind 110
      • Holybro Kopis 2
      • Bitcraze Crazyflie 2.1
    • Flight Controllers (Autopilots)
      • Pixhawk Series
        • Silicon Errata
      • Pixhawk Standard Autopilots
        • CUAV Pixhawk V6X (FMUv6X)
        • Holybro Pixhawk 6X (FMUv6X)
        • Holybro Pixhawk 6C (FMUv6C)
        • Holybro Pixhawk 6C Mini(FMUv6C)
        • Holybro Pix32 v6 (FMUv6C)
        • Holybro Pixhawk 5X (FMUv5X)
        • Holybro Pixhawk 4 (FMUv5) - Discontinued
        • Holybro Pixhawk 4 Mini (FMUv5) - Discontinued
        • Drotek Pixhawk 3 Pro (FMUv4pro)
        • mRo Pixracer (FMUv4)
        • Hex Cube Black (FMUv3)
        • mRo Pixhawk (FMUv3)
        • Holybro Pixhawk Mini (FMUv3) - Discontinued
      • Manufacturer-Supported Autopilots
        • AirMind MindPX
        • AirMind MindRacer
        • ARK Electronics ARKV6X
        • CUAV X7
        • CUAV Nora
        • CUAV V5+ (FMUv5)
        • CUAV V5 nano (FMUv5)
        • CUAV Pixhack v3 (FMUv3)
        • CubePilot Cube Orange+ (CubePilot)
        • CubePilot Cube Orange (CubePilot)
        • CubePilot Cube Yellow (CubePilot)
        • Holybro Kakute H7v2
        • Holybro Kakute H7mini
        • Holybro Kakute H7
        • Holybro Durandal
        • Holybro Pix32 v5
        • ModalAI Flight Core v1
        • ModalAI VOXL Flight
        • ModalAI VOXL 2
        • mRobotics-X2.1 (FMUv2)
        • mRo Control Zero F7)
        • NXP RDDRONE-FMUK66 FMU
        • Sky-Drones AIRLink
        • SPRacing SPRacingH7EXTREME
        • ThePeach FCC-K1
        • ThePeach FCC-R1
      • Experimental Autopilots
        • BeagleBone Blue
        • Raspberry Pi 2/3 Navio2
        • Raspberry Pi 2/3/4 PilotPi
          • PilotPi with Raspberry Pi OS
          • PilotPi with Ubuntu Server
      • Discontinued Autopilots/Vehicles
        • Drotek Dropix (FMUv2)
        • Omnibus F4 SD
        • BetaFPV Beta75X 2S Brushless Whoop
        • Bitcraze Crazyflie 2.0
        • Aerotenna OcPoC-Zynq Mini
        • CUAV v5
        • Holybro Kakute F7 (Discontinued)
        • Holybro Pixfalcon
        • Holybro pix32 (FMUv2)
        • mRo AUAV-X2
        • 3DR Pixhawk 1
        • Snapdragon Flight
        • Intel® Aero RTF Drone (Discontinued)
      • Pixhawk Autopilot Bus (PAB) & Carriers
        • ARK Electronics Pixhawk Autopilot Bus Carrier
    • Flight Controller Peripherals
      • ADSB/FLARM (Traffic Avoidance)
      • Air Traffic Avoidance: ADSB/FLARM
      • Air Traffic Avoidance: UTM
      • Airspeed Sensors
        • TFSlot Airspeed Sensor
      • Barometers
      • Camera
      • Distance Sensors (Rangefinders)
        • Lightware SFxx Lidar
        • Ainstein US-D1 Standard Radar Altimeter
        • LeddarOne Lidar
        • Benewake TFmini Lidar
        • Lidar-Lite
        • TeraRanger
        • Lanbao PSK-CM8JL65-CC5
        • Avionics Anonymous Laser Altimeter UAVCAN Interface
      • ESCs & Motors
        • PWM ESCs and Servos
        • DShot ESCs
        • OneShot ESCs and Servos
        • DroneCAN ESCs
          • Zubax Telega
          • PX4 Sapog ESC Firmware
            • Holybro Kotleta
            • Zubax Orel
        • VESC
      • TBS Crossfire (CRSF) Telemetry
      • FrSky Telemetry
      • Gimbal (Mount) Configuration
      • GPS/Compass
        • ARK GPS
        • Holybro DroneCAN M8N GPS
        • LOCOSYS Hawk A1 GNSS
        • Hex Here2
        • Holybro M8N & M9N GPS
        • Sky-Drones SmartAP GPS
      • Grippers
        • Servo Gripper
      • Optical Flow
        • ARK Flow
        • PMW3901
        • PX4FLOW (Deprecated)
      • Precision Landing
      • Parachute
      • Power Modules/PDB
        • CUAV HV pm
        • CUAV CAN PMU
        • Holybro PM02
        • Holybro PM07
        • Holybro PM06 V2
        • Holybro PM02D (digital)
        • Holybro PM03D (digital)
        • Pomegranate Systems Power Module
        • Sky-Drones SmartAP PDB
      • Satellite Coms (Iridium/RockBlock)
      • Telemetry Radios
        • SiK Radio
          • RFD900 (SiK) Telemetry Radio
          • HolyBro (SIK) Telemetry Radio
        • Telemetry Wifi
          • ESP8266 WiFi Module
          • ESP32 WiFi Module
          • 3DR Telemetry Wifi (Discontinued)
        • Microhard Serial Telemetry Radio
          • ARK Electron Microhard Serial Telemetry Radio
          • Holybro Microhard P900 Telemetry Radio
        • CUAV P8 Telemetry Radio
        • HolyBro XBP9X - Discontinued
      • RTK GPS
        • ARK RTK GPS
        • RTK GPS Heading with Dual u-blox F9P
        • CUAV C-RTK
        • CUAV C-RTK2 PPK/RTK GNSS
        • CUAV C-RTK 9Ps
        • Femtones MINI2 Receiver
        • Freefly RTK GPS
        • Holybro H-RTK-F9P
        • Holybro H-RTK-M8P
        • Holybro H-RTK Unicore UM982 GPS
        • Locosys Hawk R1
        • Locosys Hawk R2
        • Septentrio AsteRx-RIB
        • Septentrio mosaic-go
        • Trimble MB-Two
        • CubePilot Here+ (Discontined)
      • Remote ID
      • Smart Batteries
        • Rotoye Batmon Battery Smartification Kit
      • Tachometers (Revolution Counters)
        • ThunderFly TFRPM01 Tachometer Sensor
      • I2C Peripherals
        • I2C bus accelerators
        • TFI2CADT01 I2C address translator
      • CAN Peripherals
      • DroneCAN Peripherals
        • PX4 DroneCAN Firmware
        • ARK CANnode
    • Companion Computers
      • Pixhawk + Companion Setup
        • RasPi Pixhawk Companion
      • Companion Computer Peripherals
      • Holybro Pixhawk RPI CM4 Baseboard
      • Auterion Skynode
      • Computer Vision
        • Obstacle Avoidance
        • Safe Landing
        • Collision Prevention
        • Path Planning Interface
        • Motion Capture (MoCap)
        • Visual Inertial Odometry (VIO)
          • Realsense T265 Tracking Camera (VIO)
      • Video Streaming
  • Development
    • Getting Started
      • Recommended Hardware/Setup
      • Toolchain Installation
        • MacOS Setup
        • Ubuntu Setup
        • Windows Setup
        • Visual Studio Code IDE
        • Other/Generic Tools
      • Building the Code
      • Writing your First Application
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    • Concepts
      • PX4 Architecture
      • PX4 Flight Stack Architecture
        • Controller Diagrams
      • Events Interface
      • Flight Modes
      • Flight Tasks
      • Control Allocation
      • PWM limit state machine
      • System Startup
      • SD Card Layout
    • Simulation
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        • Vehicles
        • Multi-Vehicle Sim
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        • Worlds
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      • Simulate Failsafes
      • HITL Simulation
      • Simulation-In-Hardware
    • Hardware
      • Flight Controller Reference Design
      • Manufacturer’s Board Support Guide
      • Flight Controller Porting Guide
        • PX4 Board Configuration (kconfig)
        • NuttX Board Porting Guide
      • Serial Port Mapping
      • Airframes
        • Adding a New Airframe
      • Device Drivers
      • Telemetry Radio
        • SiK Radio
      • Sensor and Actuator I/O
        • DroneCAN
        • I2C Bus
        • UART/Serial Ports
          • Port-Configurable Serial Drivers
      • RTK GPS (Integration)
    • Middleware
      • uORB Messaging
      • uORB Graph
      • uORB Message Reference
        • ActionRequest
        • ActuatorArmed
        • ActuatorControlsStatus
        • ActuatorMotors
        • ActuatorOutputs
        • ActuatorServos
        • ActuatorServosTrim
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        • Airspeed
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        • CollisionConstraints
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On this page
  • PX4 Configuration
  • Companion Computer Setup
  • Trajectory Interface
  • PX4 Waypoint Interface
  • Companion Waypoint Interface
  • Companion Bezier Trajectory Interface
  • Supported Hardware
  1. Hardware (Drones&Parts)
  2. Companion Computers
  3. Computer Vision

Path Planning Interface

PreviousCollision PreventionNextMotion Capture (MoCap)

Last updated 1 year ago

PX4 uses a number of MAVLink interfaces for integrating path planning services from a companion computer (including obstacle avoidance in missions, , and future services):

  • There are two interfaces:

    • : Used by PX4 to send the desired path. May be used by path planning software to send PX4 a stream of setpoints for the planned path.

    • may (alternatively) be used by path planning software to send PX4 the planned path as a bezier curve. The curve indicates the (moving) position setpoint of the vehicle over a given time period.

  • The is used for "proof of life" detection.

  • and send the vehicle local position and altitude, respectively.

Path planning is enabled on PX4 in automatic modes (landing, takeoff, hold, mission, return) if . In these modes planning software is expected to supply setpoints to PX4; if the software cannot support a particular flight mode it must mirror back setpoints from the vehicle.

:::tip The message flows from PX4 UORB topics, through MAVLink, to ROS and back again are all documented in . :::

All services that use this interface send and receive messages of the same type/format. Developers can therefore use this interface to create their own new companion-side path planning services or tweak the existing planner software.

:::note The is recommended for developing path planning software. It comes with software pre-installed and can be used as the base for your own algorithms. :::

PX4 Configuration

Path planning is activated in PX4 by the to 1.

Companion Computer Setup

Companion-side hardware setup and hardware/software configuration is provided in the Github repo.

The actual setup/configuration required depends on the planner being used.

:::warning Only one planner can run on the companion computer at a time (at the time of writing). This means that offboard features that use different planners cannot be enabled on the same vehicle at the same time (e.g., a vehicle can support obstacle avoidance and collision prevention, but not also safe landing - or vice versa). :::

Trajectory Interface

PX4 sends information about the desired path to the companion computer (when COM_OBS_AVOID=1, in auto modes), and receives back a stream of setpoints for the planned path from the path planning software.

:::warning Route planning software should not mix these interfaces while executing a task (PX4 will use the last received message of either type). :::

PX4 Waypoint Interface

The fields set by PX4 as shown:

  • time_usec: UNIX Epoch time.

  • valid_points: 3

    • pos_x[0], pos_y[0], pos_z[0]: Type adapted x-y-z NED local position of current mission waypoint.

    • vel_x[0], vel_y[0], vel_z[0]: Type adapted x-y-z NED local velocity of current mission waypoint.

    • acc_x[0], acc_y[0], acc_z[0]: NaN

    • pos_yaw[0]: Current yaw angle

    • vel_yaw[0]: NaN

  • Point 1 - Current waypoint (Unmodified/not type adapted)):

    • pos_x[1], pos_y[1], pos_z[1]: x-y-z NED local position of current mission waypoint

    • vel_x[1], vel_y[1], vel_z[1]: NaN

    • acc_x[1], acc_y[1], acc_z[1]: NaN

    • pos_yaw[1]: Yaw setpoint

    • vel_yaw[1]: Yaw speed setpoint

  • Point 2 - Next waypoint in local coordinates (unmodified/not type adapted):

    • pos_x[2], pos_y[2], pos_z[2]: x-y-z NED local position of next mission waypoint

    • vel_x[2], vel_y[2], vel_z[2]: NaN

    • acc_x[2], acc_y[2], acc_z[2]: NaN

    • pos_yaw[2]: Yaw setpoint

    • vel_yaw[2]: Yaw speed setpoint

  • All other indices/fields are set as NaN.

Notes:

  • Point 0 is the current waypoint/target modified based on the type of target. For example, it makes sense when landing to specify the target x, y coordinates and a descent velocity. To achieve this FlightTaskAutoMapper modifies land waypoints in Point 0 to set the z component of position to NAN and the z-velocity to a desired value.

  • Points 1 and 2 are not used by the safe landing planner.

  • Point 1 is used by local and global planners.

Handling of Companion Failure

PX4 safely handles the case where messages are not received from the offboard system:

  • If no planner is running and COM_OBS_AVOID is enabled at/from boot:

    • preflight checks will fail (irrespective of vehicle mode) and it won't fly until COM_OBS_AVOID is set to 0.

  • If no planner is running and COM_OBS_AVOID is enabled after boot:

    • the vehicle will run normally in manual modes.

  • When external path planning is enabled:

    • if the HEARTBEAT is lost PX4 will emit a status message (which is displayed in QGroundControl) stating either "Avoidance system lost" or "Avoidance system timeout" (depending on the vehicle state). This is irrespective of the current flight mode.

    • A planner will mirror back setpoints it receives when the vehicle is in a mode/state for which it doesn't provide path planning. (i.e. the vehicle will follow its desired path, delayed by a very small amount). :::

Companion Waypoint Interface

The fields for the messages from the companion computer are set as shown:

  • time_usec: UNIX Epoch time.

  • valid_points: 1

  • Current vehicle information:

    • pos_x[0], pos_y[0], pos_z[0]: x-y-z NED vehicle local position setpoint

    • vel_x[0], vel_y[0], vel_z[0]: x-y-z NED velocity setpoint

    • acc_x[0], acc_y[0], acc_z[0]: NaN

    • pos_yaw[0]: Yaw angle setpoint

    • vel_yaw[0]: Yaw speed setpoint

    • command[0]: NaN.

  • All other indices/fields are set as NaN.

A planner that implements this interface must:

  • Mirror back setpoints it receives when it doesn't support planning for the current vehicle state (e.g. the local planner would mirror back messages sent during safe landing because it does not support Land mode).

Companion Bezier Trajectory Interface

The message defines the path that the vehicle should follow in terms of a curve (defined by the control points), starting at the message timestamp and reaching the final point after time delta. PX4 calculates its new setpoint (the expected current position/velocity/acceleration along the curve) using the time that the message was sent, the current time, and the total time for the curve (delta).

:::note For example, say the message was sent 0.1 seconds ago, and delta (curve duration) is 0.3s. PX4 can calculate its setpoint at the 0.1s position in the curve. :::

In more detail, the TRAJECTORY_REPRESENTATION_BEZIER is parsed as follows:

  • The number of Bezier control points determines the degree of the Bezier curve. For example, 3 points make a quadratic Bezier curve with constant acceleration.

  • The Bezier curve must be the same degree in x, y, z, and yaw, with all Bezier control points finite

  • The delta array should have the value corresponding with the last Bezier control point to indicate the duration that the waypoint takes to execute the curve to that point, from beginning to end. Other values in the delta array are ignored.

  • The timestamp of the MAVLink message should be the time that the curve starts, and communication delay and clock mismatch will be compensated for on the flight controller via the timesync mechanism.

  • Bezier curves expire after the execution time of the Bezier curve has been reached. Ensure that new messages are sent at a high enough rate and with a long enough execution time. If this does not happen the vehicle will switch to Hold mode.

Supported Hardware

The desired path information is sent by PX4 using messages, as described below in .

Path planner software sends back setpoints for the planned path using either TRAJECTORY_REPRESENTATION_WAYPOINTS (see ) or (see ). The difference is that the waypoint just specifies the next setpoint destination, while the bezier trajectory describes the exact vehicle motion (i.e. a setpoint that moves in time).

PX4 sends the desired path in messages at 5Hz.

Point 0 - Current waypoint type adapted by FlightTaskAutoMapper (see ):

command[0]: The for the current waypoint.

command[1]: The for the current waypoint.

command[2]: The for the next waypoint.

if you switch to an autonomous mode (e.g. Land Mode) it will immediately fall back to .

if a trajectory message is not received for more than 0.5 seconds and the vehicle is in an autonomous mode (Return, Mission, Takeoff, Land), the vehicle will switch into . :::note A planner must always provide points in this timeframe.

If the execution time of the last-supplied Bezier trajectory expires during path planning (when using the ), this is treated the same as not getting a new message within 0.5 seconds (i.e. vehicle switches to ).

The path planning software (running on the companion computer) may send the planned path to PX4 as a stream of messages that have the setpoint in Point 0.

Emit setpoints at more than 2Hz when receiving messages from PX4. PX4 will enter if no message is received for more than 0.5s.

The path planning software (running on the companion computer) may send the planned path to PX4 as a stream of messages.

The control points should all be specified in local coordinates ().

Tested companion computers and cameras are listed in .

TRAJECTORY_REPRESENTATION_WAYPOINTS
MAVLink Command
MAVLink Command
MAVLink Command
Hold mode
Hold mode
TRAJECTORY_REPRESENTATION_WAYPOINTS
Hold mode
TRAJECTORY_REPRESENTATION_BEZIER
MAV_FRAME_LOCAL_NED
PX4/PX4-Avoidance
TRAJECTORY_REPRESENTATION_WAYPOINTS
PX4 Waypoint Interface
TRAJECTORY_REPRESENTATION_BEZIER
Companion Waypoint Interface
Companion Bezier Trajectory Interface
notes below
Hold mode
Bezier Trajectory Interface
safe landing
MAVLink Path Planning Protocol
TRAJECTORY_REPRESENTATION_WAYPOINTS
TRAJECTORY_REPRESENTATION_BEZIER
HEARTBEAT/Connection Protocol
LOCAL_POSITION_NED
ALTITUDE
PX4/PX4-Avoidance > Message Flows
PX4 Vision Autonomy Development Kit
PX4 avoidance
setting
PX4/PX4-Avoidance
COM_OBS_AVOID=1
COM_OBS_AVOID