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ProgrammingGuide.md

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Onboard SDK Programming Guide

All structures and functions are implemented in DJI_Type.handDJI_API.h. For more details, please refer source code.

System Configuration

Before starting with the official library, developers should modify the DJI_HardDriver to inheritance the HardDriver class, implement the lock and unlock functions, together with several other virtual functions. Then to create a new API sample with your inheritanced class working as the pointer of hardware interface. And creating two life-long threads(or one, at least) running sendPoll and readPoll functions repeatedly at last. (Note: the frequency should be lower 100Hz)

We provide the example program in Linux and Windows platform with QT and pure terminal running environment.

Callback mechanism

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

Activation function in QT sample code as an example:

1.Define the callback function.

static void activationCallback(CoreAPI* This, Header* header, UserData userData);

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

api->activate(&data, DJIonboardSDK::activationCallback, this);

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

Activation

api->activate(&data, DJIonboardSDK::activationCallback, this);

Obtain/Release Control Authorization

Before obtaining Control Authorization, please ensure that:

  • The 'enable API control' box is checked in the assistant software.
  • The mode selection bar of the remote controller is placed at the F position.
api->setControl(true, DJIonboardSDK::setControlCallback, this);

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).

flight->task(type);

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 Autopilot，horizontal velocity control(HORI_VEL)related control modes can be used.
FlightData data;
data.flag = flightFlag;
data.x = flightx;
data.y = flighty;
data.z = flightz;
data.yaw = flightyaw;
flight->setFlight(&data);

Receive Flight Data

If developers want to get Flight Data, please check corresponding item in DJI 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
typedef struct QuaternionData
{
    float32_t q0;
    float32_t q1;
    float32_t q2;
    float32_t q3;
} QuaternionData;

QuaternionData q;

2、Get the quaternion

q = flight->getQuaternion()

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

typedef struct BroadcastData
{
    unsigned short dataFlag;
    TimeStampData timeStamp;
    QuaternionData q;
    CommonData a;
    VelocityData v;
    CommonData w;
    PossitionData pos;
    MagnetData mag;
    RadioData rc;
    GimbalData gimbal;
    FlightStatus status;
    BatteryData battery;
    CtrlInfoData ctrlInfo;

    //! @note these variables are not send from FMU,
    //! just a record for user.
    uint8_t controlStatus;
    uint8_t activation;
} BroadcastData;

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 */

FlightData data;
data.flag = 0x90;
data.x = offset_x;
data.y = offset_y;
data.z = target_z;
data.yaw = target_yaw;
flight->setFlight(&data);