How intepret the results from BNO085 sensor?

Other Hardware Sensors
1

Hi!

I'm testing my new sensor BNO085 and I want to determine the boat's course. I use the ready-made code from the examples (SH2_ROTATION_VECTOR - determining the course based on data from accelerometer, gyroscope and magnetometer). I get the result in quaternions, then I transform them into Eulerians and degrees - function below:

void quaternionToEuler(float qr, float qi, float qj, float qk, euler_t* ypr, bool degrees) {
  Serial.println(RAD_TO_DEG);

    float sqr = sq(qr);
    float sqi = sq(qi);
    float sqj = sq(qj);
    float sqk = sq(qk);

    ypr->yaw = atan2(2.0 * (qi * qj + qk * qr), (sqi - sqj - sqk + sqr));
    ypr->pitch = asin(-2.0 * (qi * qk - qj * qr) / (sqi + sqj + sqk + sqr));
    ypr->roll = atan2(2.0 * (qj * qk + qi * qr), (-sqi - sqj + sqk + sqr));

    if (degrees) {
      ypr->yaw *= RAD_TO_DEG;
      ypr->pitch *= RAD_TO_DEG;
      ypr->roll *= RAD_TO_DEG;
    }
}

According to the documentation, the Y axis marked on the sensor points north (screen below), so if the sensor receives a result of 0, then north is where the Y axis points on the sensor?

image
image627×781 68.7 KB

2

No, the result will be 1+0i+0j+0k, top row in that table. A result of 0 is not valid, rotations represented as quaternions have magnitude 1, ie a^2+b^2+c^2+d^2 = 1, where a,b,c,d are the coefficients of 1,i,j,k

3

okey, so how interpet the result in euler and then in deegres from this function? For example, I have a 90 deegres and this is a East. So in which direction (which axis on sensor) is East?

4

I check this now. You have right, where I received for examaple 0+0i+0j+1k the Y axis pointed at South so this is agree with documentation.

5

Dealing with 3D angle representations always requires a cool head to get things right (or just try all the variants as there's only a finite number!)

At least with quaternions a rotation is relatively intuitive, the vector part of the quarternion gives the axis of rotation, the scalar part the angle (more exactly the cosine of half the angle)

6

Thanks for your answer. I tested my results and it's ok, but I have to design arm to sensor calibrate (in three axis).

7

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