void getHeading(void)
{
    heading = 180 * atan2(Mxyz[1], Mxyz[0]) / PI;
    if (heading < 0) heading += 360;
}

void getTiltHeading(void)
{
    float pitch = asin(-Axyz[0]);
    float roll = asin(Axyz[1] / cos(pitch));

    float xh = Mxyz[0] * cos(pitch) + Mxyz[2] * sin(pitch);
    float yh = Mxyz[0] * sin(roll) * sin(pitch) + Mxyz[1] * cos(roll) - Mxyz[2] * sin(roll) * cos(pitch);
    float zh = -Mxyz[0] * cos(roll) * sin(pitch) + Mxyz[1] * sin(roll) + Mxyz[2] * cos(roll) * cos(pitch);
    tiltheading = 180 * atan2(yh, xh) / PI;
    if (yh < 0)    tiltheading += 360;
}



void Mxyz_init_calibrated ()
{

    Serial.println(F("Before using 9DOF,we need to calibrate the compass frist,It will takes about 2 minutes."));
    Serial.print("  ");
    Serial.println(F("During  calibratting ,you should rotate and turn the 9DOF all the time within 2 minutes."));
    Serial.print("  ");
    Serial.println(F("If you are ready ,please sent a command data 'ready' to start sample and calibrate."));
    while (!Serial.find("ready"));
    Serial.println("  ");
    Serial.println("ready");
    Serial.println("Sample starting......");
    Serial.println("waiting ......");

    get_calibration_Data ();

    Serial.println("     ");
    Serial.println("compass calibration parameter ");
    Serial.print(mx_centre);
    Serial.print("     ");
    Serial.print(my_centre);
    Serial.print("     ");
    Serial.println(mz_centre);
    Serial.println("    ");
}


void get_calibration_Data ()
{
    for (int i = 0; i < sample_num_mdate; i++)
    {
        get_one_sample_date_mxyz();
        /*
        Serial.print(mx_sample[2]);
        Serial.print(" ");
        Serial.print(my_sample[2]);                            //you can see the sample data here .
        Serial.print(" ");
        Serial.println(mz_sample[2]);
        */



        if (mx_sample[2] >= mx_sample[1])mx_sample[1] = mx_sample[2];
        if (my_sample[2] >= my_sample[1])my_sample[1] = my_sample[2]; //find max value
        if (mz_sample[2] >= mz_sample[1])mz_sample[1] = mz_sample[2];

        if (mx_sample[2] <= mx_sample[0])mx_sample[0] = mx_sample[2];
        if (my_sample[2] <= my_sample[0])my_sample[0] = my_sample[2]; //find min value
        if (mz_sample[2] <= mz_sample[0])mz_sample[0] = mz_sample[2];

    }

    mx_max = mx_sample[1];
    my_max = my_sample[1];
    mz_max = mz_sample[1];

    mx_min = mx_sample[0];
    my_min = my_sample[0];
    mz_min = mz_sample[0];



    mx_centre = (mx_max + mx_min) / 2;
    my_centre = (my_max + my_min) / 2;
    mz_centre = (mz_max + mz_min) / 2;

}






void get_one_sample_date_mxyz()
{
    getCompass_Data();
    mx_sample[2] = Mxyz[0];
    my_sample[2] = Mxyz[1];
    mz_sample[2] = Mxyz[2];
}


void getAccel_Data(void)
{
    accelgyro.getMotion9(&ax, &ay, &az, &gx, &gy, &gz, &mx, &my, &mz);
    Axyz[0] = (double) ax / 16384;
    Axyz[1] = (double) ay / 16384;
    Axyz[2] = (double) az / 16384;
}

void getGyro_Data(void)
{
    accelgyro.getMotion9(&ax, &ay, &az, &gx, &gy, &gz, &mx, &my, &mz);
    Gxyz[0] = (double) gx * 250 / 32768;
    Gxyz[1] = (double) gy * 250 / 32768;
    Gxyz[2] = (double) gz * 250 / 32768;
}

void getCompass_Data(void)
{
    I2C_M.writeByte(MPU9150_RA_MAG_ADDRESS, 0x0A, 0x01); //enable the magnetometer
    delay(10);
    I2C_M.readBytes(MPU9150_RA_MAG_ADDRESS, MPU9150_RA_MAG_XOUT_L, 6, buffer_m);

    mx = ((int16_t)(buffer_m[1]) << 8) | buffer_m[0] ;
    my = ((int16_t)(buffer_m[3]) << 8) | buffer_m[2] ;
    mz = ((int16_t)(buffer_m[5]) << 8) | buffer_m[4] ;

    Mxyz[0] = (double) mx * 1200 / 4096;
    Mxyz[1] = (double) my * 1200 / 4096;
    Mxyz[2] = (double) mz * 1200 / 4096;
}

void getCompassDate_calibrated ()
{
    getCompass_Data();
    Mxyz[0] = Mxyz[0] - mx_centre;
    Mxyz[1] = Mxyz[1] - my_centre;
    Mxyz[2] = Mxyz[2] - mz_centre;
}