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Onboard SDK Programming Guide

All structures and functions are implemented in DJI_Pro_App.cpp. For more details, please refer source code.

Callback mechanism

For all commands which has return value mentioned in OPEN Protocol, developers can get the return value by callback functions.

Activation function as an example:

1.Define the callback function.

void cb_user_notice(unsigned short result)  
{  
    printf("Activation result is %d \r\n", result);  
}

2.Pass the name of callback function when you call to activate.

DJI_Pro_Activate_API(&user_act_data, cb_user_notice);

3.The meaning of return values(result) is explained in each commands in OPEN Protocol.

Initialization (for linux)

{
    int baudrate = 115200;
    char uart_name[32] = {"/dev/ttyUSB0"};
    Pro_Hw_Setup(uart_name,baudrate);
    DJI_Pro_Setup(NULL);
}

Activation

activate_data_t user_act_data; 
{
    

    char key_buf[65] = "Input-your-app_key-here";   /* Input your app_key */
    char app_bundle_id[32] = "1234567890";

    user_act_data.app_id = 10086;                   /* Input your app_id */
    user_act_data.app_api_level = 2;                /* Input your app_level */
    user_act_data.app_ver = 0x02030A00; 
    user_act_data.app_key = key_buf;  
    strcpy((char*)user_act_data.app_bundle_id, app_bundle_id);

    DJI_Pro_Activate_API(&user_act_data,NULL);
}

Obtain/Release Control Authorization

Before obtaining Control Authorization, please ensure that:

  • The 'enable API control' box is checked in the N1 assistant software.
  • The IOC mode inside the DJI GO APP is off.
  • The mode selection bar of the remote controller is placed at the F position.
/* Get controller */
DJI_Pro_Control_Management(1,NULL);
/* Release controller */
DJI_Pro_Control_Management(0,NULL);

Take off, Land and Return to home (RTH)

The return value of this function please refer to Request Switch Result(Below codes do not use callback function).

/* Take off */
DJI_Pro_Status_Ctrl(4,NULL);
/* Land */
DJI_Pro_Status_Ctrl(6,NULL);
/* Return to home */
DJI_Pro_Status_Ctrl(1,NULL);

Movement Control

We recommend developers to send yours Movement Control commands in 50Hz frequency. Developers can implement that by usleep(20000)、ros::Duration(1/50) or other ways which depend on the develop environment.

In Movement Control, specific meanings of arguements are decided by control mode byte. For more info about Movement Control, please refer to Control mode byte part in Appendix.

We recommend developers to use HORI_POS mode in horizontal movement. More details are shown in Position Control in this document. In this mode, speed and attitude are controlled by autopilot, thus developers do not concern about that.

Please note that if the following conditions are met that the control mode is functional:

  • Only when the GPS signal is good (health_flag >=3)，horizontal position control (HORI_POS) related control modes can be used.
  • Only when GPS signal is good (health_flag >=3)，or when Gudiance system is working properly with N1 Autopilot，horizontal velocity control(HORI_VEL)related control modes can be used.
{
    attitude_data_t user_ctrl_data;

    while(1)
    {
        user_ctrl_data.ctrl_flag = 0x40;                /* control_mode_byte */
        user_ctrl_data.roll_or_x = 0;
        user_ctrl_data.pitch_or_y = 2;
        user_ctrl_data.thr_z = 0;
        user_ctrl_data.yaw = 0;
        DJI_Pro_Attitude_Control(&user_ctrl_data);  

        usleep(20000);                                  /* 50 Hz */ 
    }
}

Receive Flight Data

If developers want to get Flight Data, please check corresponding item in DJI N1 assistant software. And examine the coordinate of part data.

Developers need to declare correct structure variables to save Flight Data.

Get quaternion as an example:

  1. Declare quaternion struction
    api_quaternion_data_t quat;
  1. Get the quaternion
    DJI_Pro_Get_Quaternion(&quat);

Other data types and functions to obtain the corresponding data sent outside from autopilot, please refer DJI_Pro_App.h.

GPS to North-East Coordinate

Convert GPS to North-East Coordinate. (GPS in radian，North-East Coordinate in meter)

For example, origin_longti and origin_lati , as the longitude and latitude of original position，are decided by developers and the position of UAV taking off is recommended to be the original position. longti and lati are longitude and latitude of UAV's current posistion. x and y are offset to the original position in the North and the East directions. The unit of offset is meter.

#define C_EARTH (double) 6378137.0
/* From GPS to Ground */
{
    double dlati = lati-origin_lati;
    double dlongti= longti-origin_longti;

    double x = dlati * C_EARTH;
    double y = dlongti * C_EARTH * cos(lati / 2.0 + origin_lati / 2.0);
}

Quaternion to RPY

Convert quaternion to roll, pitch and yaw in radian in body coordinate.

    api_quaternion_data_t q;
    DJI_Pro_Get_Quaternion(&q);

    float roll  = atan2(2.0 * (q.q3 * q.q2 + q.q0 * q.q1) , 1.0 - 2.0 * (q.q1 * q.q1 + q.q2 * q.q2));
    float pitch = asin(2.0 * (q.q2 * q.q0 - q.q3 * q.q1));
    float yaw   = atan2(2.0 * (q.q3 * q.q0 + q.q1 * q.q2) , - 1.0 + 2.0 * (q.q0 * q.q0 + q.q1 * q.q1));

Position Control(HORI_POS)

The input horizatal arguements is the offset between current position and target position, when HORI_POS as the mode of horizatal movement control. The unit of offset is meter.

For example, in ground frame, target is target position and current is UAV's current position. The coordinates of these positions are caculated by GPS, Guidance or other sensors. In most cases, GPS is a correct way to do this work.

Because, to autopilot, the maximum frequency of receiving data is 50Hz, the frequency of caculating off set should be over 50Hz to ensure the controlling is vaild.

void update_offset()
{
    offset_x = target_x - current_x;
    offset_y = target_y - current_y;
}


/* Command thread */
attitude_data_t user_ctrl_data;

/* HORI_POS|VERT_VEL|YAW_RATE|HORI_GROUND_FRAME|YAW_GROUND_FRAME */
user_ctrl_data.ctrl_flag = 0x88;
user_ctrl_data.thr_z = 0;
user_ctrl_data.yaw = 0;

while(1)                                            
{
    update_offset();
    if (/*offset is small enough*/)
        break;
    user_ctrl_data.roll_or_x = offset_x;
    user_ctrl_data.pitch_or_y = offset_y;
    
    DJI_Pro_Attitude_Control(&user_ctrl_data);

    usleep(20000);                                  /* 50 Hz */
}