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Problem with Heading Calculation

gtk
Associate

‎2025-03-16 8:36 PM - edited ‎2025-03-16 11:29 PM

I'm using ST MotionFX v2.7.1 and have encountered an issue with heading calculation.

I'm following the sample code from the document:
um2220-getting-started-with-motionfx-sensor-fusion-library-in-xcubemems1-expansion-for-stm32cube-stmicroelectronics

 

#define STATE_SIZE (size_t)(2450)
static uint8_t mfxstate[STATE_SIZE];
MFX_knobs_t iKnobs;
MFX_input_t data_in_scale;

void main() {
    /* Sensor Fusion API initialization function */
    MotionFX_initialize((MFXState_t *)mfxstate);

    /* Modify knobs settings & set the knobs */
    MotionFX_getKnobs((MFXState_t *)mfxstate, &iKnobs);

    iKnobs.LMode = 2;
    iKnobs.modx = 1;
    iKnobs.output_type = 1;
    iKnobs.start_automatic_gbias_calculation = 1;
  
    //orientation

    MotionFX_setKnobs((MFXState_t *)mfxstate, &iKnobs);

    MotionFX_enable_6X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);
    MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);

    /* Enable 9-axis sensor fusion */
    MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_ENABLE);

    // init last_time
    clock_gettime(CLOCK_MONOTONIC, &last_time);

    get_sensor_data_scale(&data_in_scale);

    MFX_input_t sensor_in;
    MFX_output_t sensor_out;

    for(int i =0; i< 9999999999; i++)
    {
        get_sensor_data(&sensor_in);

        float delta_time = get_delta_time();
        MotionFX_propagate((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time);
        MotionFX_update((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time, NULL);

        printf("Heading: %f\n", sensor_out.heading);
    }
}

 

 

When I run the code, the heading value is incorrect. However, if I re-run MotionFX_initialize, the heading calculation becomes correct.

 

#define STATE_SIZE (size_t)(2450)
static uint8_t mfxstate[STATE_SIZE];
MFX_knobs_t iKnobs;
MFX_input_t data_in_scale;

void main() {
    for(int i =0; i< 9999999999; i++)
    {
        /* Sensor Fusion API initialization function */
        MotionFX_initialize((MFXState_t *)mfxstate);

        /* Modify knobs settings & set the knobs */
        MotionFX_getKnobs((MFXState_t *)mfxstate, &iKnobs);

        iKnobs.LMode = 2;
        iKnobs.modx = 1;
        iKnobs.output_type = 1;
        iKnobs.start_automatic_gbias_calculation = 1;

        //orientation

        MotionFX_setKnobs((MFXState_t *)mfxstate, &iKnobs);

        MotionFX_enable_6X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);
        MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_DISABLE);

        /* Enable 9-axis sensor fusion */
        MotionFX_enable_9X((MFXState_t *)mfxstate, MFX_ENGINE_ENABLE);

        // init last_time
        clock_gettime(CLOCK_MONOTONIC, &last_time);

        get_sensor_data_scale(&data_in_scale);

        MFX_input_t sensor_in;
        MFX_output_t sensor_out;

        get_sensor_data(&sensor_in);

        float delta_time = get_delta_time();
        MotionFX_propagate((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time);
        MotionFX_update((MFXState_t *)mfxstate, &sensor_out, &sensor_in, &delta_time, NULL);

        printf("Heading: %f\n", sensor_out.heading);
    }
}

 

 

Does anyone know why this happens? Any insights would be greatly appreciated! Let me know if you need more details.

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2 REPLIES 2
Federica Bossi
ST Employee

‎2025-03-21 1:52 AM

Hi @gtk ,

Can you share the outputs you get in both cases?

Thanks!

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gtk
Associate
In response to Federica Bossi

‎2025-03-25 1:50 AM 

//without 9x

mag: [-0.208000, -0.996000, 0.565000]
acc: [9.514451, 1.042671, 0.016750]
gyro: [0.009163, -0.059559, 0.056047]
Yaw: 350.114685, Pitch: -0.101226, Roll: 6.254028
Quaternion: [W=0.005579, X=-0.054271, Y=0.086079, Z=0.994794]
Gravity: [X=-0.108937, Y=-0.001756, Z=-0.994047]
Linear Acceleration: [X=0.933735, Y=0.014994, Z=8.520404]
Heading: 350.114685
Heading Error: 0.417009
==============================
mag: [-0.214000, 0.873000, 0.604000]
acc: [9.762706, 1.114456, -0.442074]
gyro: [-0.070555, -0.111177, 0.226325]
Yaw: 350.849396, Pitch: 2.392230, Roll: 6.477042
Quaternion: [W=-0.016269, X=-0.057963, Y=0.078449, Z=0.995099]
Gravity: [X=-0.112805, Y=0.041474, Z=-0.992751]
Linear Acceleration: [X=1.001651, Y=-0.400600, Z=8.769955]
Heading: 350.849396
Heading Error: 0.300941
==============================
mag: [-0.214000, 0.858000, 0.616000]
acc: [9.881749, 0.461216, -0.324825]
gyro: [-0.071166, -0.021686, -0.625525]
Yaw: 5.967731, Pitch: 2.589645, Roll: 4.119998
Quaternion: [W=-0.024422, X=-0.034713, Y=-0.052819, Z=0.997702]
Gravity: [X=-0.071846, Y=0.045066, Z=-0.996397]
Linear Acceleration: [X=0.389371, Y=-0.279760, Z=8.885352]
Heading: 5.967731
Heading Error: 0.106927
==============================
mag: [-0.115000, 0.807000, 0.649000]
acc: [9.217143, 0.588634, 0.117248]
gyro: [-0.707075, -0.092699, -0.029016]
Yaw: 6.942193, Pitch: 0.362013, Roll: 3.827046
Quaternion: [W=-0.005173, X=-0.033138, Y=-0.060616, Z=0.997598]
Gravity: [X=-0.066745, Y=0.006304, Z=-0.997750]
Linear Acceleration: [X=0.521889, Y=0.123552, Z=8.219393]
Heading: 6.942193
Heading Error: 0.091870
==============================
mag: [0.053000, 0.789000, 0.685000]
acc: [9.414551, 0.581455, -0.057428]
gyro: [-1.808310, -0.272140, 0.388510]
Yaw: 7.401766, Pitch: 0.368290, Roll: 3.591856
Quaternion: [W=-0.005229, X=-0.031067, Y=-0.064616, Z=0.997413]
Gravity: [X=-0.062649, Y=0.006415, Z=-0.998015]
Linear Acceleration: [X=0.518807, Y=-0.051012, Z=8.416535]
Heading: 7.401766
Heading Error: 0.089419
==============================

 

//with 9x

mag: [0.056000, 0.906000, 0.580000]
acc: [9.843464, 0.562313, 0.478564]
gyro: [0.030390, 0.082467, 0.527176]
Yaw: 0.548519, Pitch: -2.783378, Roll: 3.265410
Quaternion: [W=0.024141, X=-0.028600, Y=-0.004091, Z=0.999291]
Gravity: [X=-0.056961, Y=-0.048481, Z=-0.997199]
Linear Acceleration: [X=0.505351, Y=0.430083, Z=8.846266]
Heading: 0.548519
Heading Error: 0.100627
==============================
mag: [0.026000, 0.921000, 0.583000]
acc: [9.811160, -0.222532, 1.222133]
gyro: [0.006414, 1.013576, 0.492967]
Yaw: 3.713483, Pitch: -7.100546, Roll: -1.289394
Quaternion: [W=0.062252, X=0.009218, Y=-0.033033, Z=0.997471]
Gravity: [X=0.022502, Y=-0.123580, Z=-0.992079]
Linear Acceleration: [X=-0.200030, Y=1.098553, Z=8.819080]
Heading: 3.713483
Heading Error: 0.049027
==============================
mag: [0.059000, 0.945000, 0.547000]
acc: [9.217143, -0.576670, 0.567098]
gyro: [-0.872772, 0.035125, 0.729219]
Yaw: 10.832839, Pitch: -3.520864, Roll: -3.573319
Quaternion: [W=0.033510, X=0.028126, Y=-0.095257, Z=0.994491]
Gravity: [X=0.062326, Y=-0.061293, Z=-0.996172]
Linear Acceleration: [X=-0.514344, Y=0.505806, Z=8.220971]
Heading: 10.832839
Heading Error: 0.064499
==============================
mag: [0.191000, 0.963000, 0.472000]
acc: [10.156923, -0.013759, 3.787236]
gyro: [-1.945602, 0.439211, -0.312762]
Yaw: 13.846349, Pitch: -20.449083, Roll: -0.072748
Quaternion: [W=0.176287, X=-0.020776, Y=-0.118736, Z=0.976930]
Gravity: [X=0.001270, Y=-0.349375, Z=-0.936982]
Linear Acceleration: [X=-0.012489, Y=3.437861, Z=9.219941]
Heading: 13.846349
Heading Error: 0.046600
==============================
mag: [0.083000, 0.939000, 0.535000]
acc: [9.631699, -0.590428, 0.399003]
gyro: [-0.426230, 0.458759, 0.186466]
Yaw: 13.611735, Pitch: -2.372174, Roll: -3.504874
Quaternion: [W=0.024167, X=0.027907, Y=-0.119053, Z=0.992201]
Gravity: [X=0.061133, Y=-0.041313, Z=-0.997274]
Linear Acceleration: [X=-0.529295, Y=0.357690, Z=8.634424]
Heading: 13.611735
Heading Error: 0.064753
==============================
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