The psdk_ros2 wrapper

This brief overview highlights the primary components and their roles within the psdk_ros2 wrapper’s code structure.

├── psdk_interfaces : provides the main interfaces (msg, srv)
├── psdk_wrapper : main wrapper code

Within the psdk_wrapper folder you can find:

• 3rdparty: folder contains essential libraries sourced from DJI Payload-SDK for FCU interaction which had required small modifications

• psdk_wrapper.cpp: main lifecycle node which set-up and initializes the psdk application

• modules: encapsulates specific functionalities of the wrapper

Modules

Telemetry

This module subscribes to the main data exposed by the PSDK libraries and publishes it on ROS 2 topics.

Available topics

Given the high number of topics available, these have been grouped under different categories mimicking the options from DJI Assistant 2. Below you can find the topics currently available as well as the maximum frequency at which you can retrieve them. Note that these frequencies are different depending on the drone model you are using. The latest information of the maximum frequency of each topic and the corresponding drones can be found in this table.

• IMU

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/imu	400 Hz	50 Hz	400 Hz

• Attitude

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/attitude	200 Hz	50 Hz	200 Hz

• Acceleration

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/acceleration_ground_fused	200 Hz	50 Hz	200 Hz
psdk_ros2/acceleration_body_fused	200 Hz	50 Hz	200 Hz
psdk_ros2/acceleration_body_raw	400 Hz	50 Hz	400 Hz

• Velocity

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/velocity_ground_fused	200 Hz	50 Hz	200 Hz

• Angular Velocity

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/angular_rate_ground_fused	200 Hz	50 Hz	200 Hz
psdk_ros2/angular_rate_body_raw	400 Hz	50 Hz	400 Hz

• Position

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/position_fused	200 Hz	50 Hz	200 Hz

• Altitude

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/altitude_sea_level	200 Hz	50 Hz	200 Hz
psdk_ros2/altitude_barometric	200 Hz	50 Hz	200 Hz

• GPS Data

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/gps_position_fused	200 Hz	50 Hz	200 Hz
psdk_ros2/gps_position	5 Hz	50 Hz	5 Hz
psdk_ros2/gps_velocity	5 Hz	50 Hz	5 Hz
psdk_ros2/gps_details	5 Hz	50 Hz	5 Hz
psdk_ros2/gps_signal_level	50 Hz	50 Hz	50 Hz
psdk_ros2/gps_control_level	5 Hz	50 Hz	5 Hz

• RTK Data

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/rtk_position	5 Hz	50 Hz	5 Hz
psdk_ros2/rtk_velocity	5 Hz	50 Hz	5 Hz
psdk_ros2/rtk_yaw	5 Hz	50 Hz	5 Hz
psdk_ros2/rtk_position_info	5 Hz	50 Hz	5 Hz
psdk_ros2/rtk_yaw_info	5 Hz	50 Hz	5 Hz

• Magnetometer

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/magnetic_field	100 Hz	50 Hz	100 Hz

• RC Channels Data

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/rc	50 Hz	50 Hz	50 Hz

• Gimbal Data

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/gimbal_angles	50 Hz	50 Hz	50 Hz
psdk_ros2/gimbal_status	50 Hz	-	50 Hz

• Flight Status

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/flight_status	50 Hz	50 Hz	50 Hz
psdk_ros2/display_mode	50 Hz	50 Hz	50 Hz
psdk_ros2/landing_gear_status	50 Hz	-	50 Hz
psdk_ros2/motor_start_error	50 Hz	-	50 Hz
psdk_ros2/flight_anomaly	50 Hz	50 Hz	50 Hz

• Battery Level

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/battery	50 Hz	-	50 Hz
psdk_ros2/psdk_ros2/single_battery_index1	50 Hz	50 Hz	50 Hz
psdk_ros2/psdk_ros2/single_battery_index2	50 Hz	50 Hz	50 Hz

• Control Information

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/height_above_ground	200 Hz	-	200 Hz
psdk_ros2/control_mode	50 Hz	50 Hz	50 Hz
psdk_ros2/home_point	50 Hz	50 Hz	50 Hz
psdk_ros2/home_point_status	50 Hz	50 Hz	50 Hz
psdk_ros2/home_point_altitude	1 Hz	50 Hz	1 Hz
psdk_ros2/relative_obstacle_info	100 Hz	50 Hz	100 Hz

• Health Management System (HMS)

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/hms_info_table	1 Hz	1 Hz	1 Hz

• ESC Data

ROS 2 Topic	M300 RTK	Matrice 30/30T	M350 RTK
psdk_ros2/esc_data	50 Hz	50 Hz	50 Hz

The user can set a specific publishing frequency to each category within the psdk_params.yaml file and this will be applied to all topics contained within it. The possible frequencies that can be set for any given category are: 1, 5, 10, 50, 100, 200, 400 Hz. If the frequency set by the user is higher than the maximum one handled internally by the PSDK libraries, an error message will appear. Setting a high number of topics to the maximum frequency may prevent some topics from initializing or may reduce the update frequency of certain topics. Please consider using a moderate number of topics to optimize performance and ensure all topics initialize properly.

Note: If 0 Hz frequency is set, the publisher of that topic will be disabled.

Coordinate frames

This wrapper is using the ROS standard convention REP 103 and REP 105. Thus, it transforms the FCU typical coordinate frames NED/FRD to ROS standards ENU/FLU. It is known, that there is room for improvement in the current implementation, thus users of this repo are asked to report any issue encountered and open PRs to improve the quality and robustness of the code.

Flight control

The following topics are exposed to send commands to the FCU of the aircraft:

/psdk_ros2/flight_control_setpoint_ENUposition_yaw

• Message Type: sensor_msgs::msg::Joy

• axes[0]: x command [m]

• axes[1]: y command [m]

  Warning:

  These commands are relative. Thus, the aircraft does not stop upon reaching the provided X/Y commands!! The low-level implementation of this functionality lacks a position controller for these axes. If this is desired, the user should implement his/hers own way of sending an XY command and stopping once the aircraft reaches it.

• axes[2]: z command [m]

  • This command is relative to the global Cartesian frame where the aircraft has been initialized.

  • The aircraft will stop at the designated z command once it reaches it.

• axes[3]: yaw command [rad]

  • The commanded yaw is assumed to be following REP 103, thus a FLU rotation wrt to ENU frame

  • The aircraft will stop at the designated yaw command once it reaches it.

/psdk_ros2/flight_control_setpoint_ENUvelocity_yawrate

These commands are with respect to a ENU oriented global Cartesian frame where the aircraft has been initialized.

• Message Type: sensor_msgs::msg::Joy

• axes[0]: x velocity command [m/s]

• axes[1]: y velocity command [m/s]

• axes[2]: z velocity command [m/s]

• axes[3]: yaw rate command [rad/s]

/psdk_ros2/flight_control_setpoint_FLUvelocity_yawrate

These commands are with respect to a body frame (FLU).

• Message Type: sensor_msgs::msg::Joy

• axes[0]: x velocity command [m/s]

• axes[1]: y velocity command [m/s]

• axes[2]: z velocity command [m/s]

• axes[3]: yaw rate command [rad/s]

/psdk_ros2/flight_control_setpoint_generic

• WIP: currently not implemented

/psdk_ros2/flight_control_setpoint_rollpitch_yawrate_thrust

• WIP: currently not implemented

Camera

This module implements the main functionalities related with different camera payloads that can be mounted on-board the copter. The PSDK libraries define a payload index for each camera mounted on-board a copter as follows:

typedef enum {
    DJI_MOUNT_POSITION_UNKNOWN = 0,
    DJI_MOUNT_POSITION_PAYLOAD_PORT_NO1 = 1,
    DJI_MOUNT_POSITION_PAYLOAD_PORT_NO2 = 2,
    DJI_MOUNT_POSITION_PAYLOAD_PORT_NO3 = 3,
    DJI_MOUNT_POSITION_EXTENSION_PORT = 4,
} E_DjiMountPosition;

Thus, when calling any of the services explained below, first the payload index or mount position needs to be specified so that the proper camera is selected. By default, the payload index is set to 1 in many services.

Camera settings

The following camera parameters can be set/get. Please note, that some of these are not available for all camera types or need the camera to be put in a particular mode before the parameter can be set. Check the API Documentation for more information regaring the inputs and outputs of these ROS 2 services.

Name	Type
psdk_ros2/camera_get_type	Service
psdk_ros2/camera_set_exposure_mode_ev	Service
psdk_ros2/camera_get_exposure_mode_ev	Service
psdk_ros2/camera_set_shutter_speed	Service
psdk_ros2/camera_get_shutter_speed	Service
psdk_ros2/camera_set_iso	Service
psdk_ros2/camera_get_iso	Service
psdk_ros2/camera_set_focus_target	Service
psdk_ros2/camera_get_focus_target	Service
psdk_ros2/camera_set_focus_mode	Service
psdk_ros2/camera_get_focus_mode	Service
psdk_ros2/camera_set_optical_zoom	Service
psdk_ros2/camera_get_optical_zoom	Service
psdk_ros2/camera_set_infrared_zoom	Service
psdk_ros2/camera_set_aperture	Service
psdk_ros2/camera_get_aperture	Service
psdk_ros2/camera_get_laser_ranging_info	Service

Camera commands

The following services can be called to start shooting photos or record videos with the payload installed on-board the copter. Check the API Documentation for more information regarding the inputs and outputs of these ROS 2 services.

Name	Type
psdk_ros2/camera_shoot_single_photo	Service
psdk_ros2/camera_shoot_burst_photo	Service
psdk_ros2/camera_shoot_interval_photo	Service
psdk_ros2/camera_stop_shoot_photo	Service
psdk_ros2/camera_record_video	Service

Camera streaming

The camera streaming is managed by a ROS 2 service. Calling the psdk_ros2/camera_setup_streaming you can select the payload index of the camera you want to stream, the camera source (e.g. zoom camera/wide camera) and whether to start or stop the streaming with a boolean. Moreover, one can set if the stream should be published decoded or encoded. Once the streaming is started, you can see the images either on the psdk_ros2/main_camera_stream if the main camera has been selected or the psdk_ros2/fpv_camera_stream if the FPV camera has been selected.

Please notice that the frequency of the streaming will depend on the computational resources available on the board where the psdk_ros2 wrapper is launched.

Name	Type
psdk_ros2/camera_setup_streaming	Service
psdk_ros2/main_camera_stream	Topic
psdk_ros2/fpv_camera_stream	Topic

Camera file management

Camera services for managing the SD card storage from the DJI payload. Calling the psdk_ros2/camera_get_file_list_info returns as a result the number of files and an array of file data. With this information you are able to manipulate the objects inside the SD card by calling the other services like psdk_ros2/camera_download_file_by_index or psdk_ros2/camera_delete_file_by_index. Inside these services you need to specify the location where the files will be saved. You can configure the path for the file download via a ROS 2 parameter (see psdk_params.yml).

Moreover, one can check the current storage capacity of the SD card (psdk_ros2/camera_get_sd_storage_info) and format it if desired (psdk_ros2/camera_format_sd_card).

Name	Type
psdk_ros2/camera_get_file_list_info	Service
psdk_ros2/camera_download_file_by_index	Action
psdk_ros2/camera_delete_file_by_index	Action
psdk_ros2/camera_get_sd_storage_info	Service
psdk_ros2/camera_format_sd_card	Service

Gimbal

Name	Type
psdk_ros2/gimbal_set_mode	Service
psdk_ros2/gimbal_reset	Service
psdk_ros2/gimbal_rotation	Publisher
psdk_ros2/gimbal_angles	Topic

Perception

The perception stereo streaming is managed by a ROS 2 service. Calling the psdk_ros2/start_perception you can select the direction of the stereo camera you want to stream (e.g. DOWN, FRONT, REAR, UP, LEFT, RIGHT) and whether to start or stop the streaming with a boolean. Once the streaming is started, you can see the images for left side stereo camera on the psdk_ros2/perception_stereo_left_stream and for right side stereo camera on the psdk_ros2/perception_stereo_right_stream. Currently only one direction stereo cameras (both left and right) feed can be access at a time.

Moreover, one can get the camera parameters on the psdk_ros2/perception_camera_parameters

Name	Type
psdk_ros2/start_perception	Service
psdk_ros2/perception_stereo_left_stream	Topic
psdk_ros2/perception_stereo_right_stream	Topic
psdk_ros2/perception_camera_parameters	Topic