如何获得独立于设备旋转的磁场矢量? [英] How can I get the magnetic field vector, independent of the device rotation?

问题描述

我想要存档的是一种位置的磁性指纹".我使用 MAGNETIC_FIELD 传感器，如果我得到 3 个值对于(不幸的是没有进一步解释)X、Y 和 Z 轴.

What I want to archieve is a sort of "magnetic fingerprint" of a location. I use the MAGNETIC_FIELD sensor and in the event I get the 3 values for the (unfortunately not further explained) X, Y and Z axis.

问题是，随着我旋转设备，这些值会发生变化，所以我猜 3 轴是相对于设备的.我需要的是补偿设备旋转，以便我获得相同的 3 个值，无论设备如何旋转.

Problem is, that the values change as I rotate the device, so I guess the 3 axis are relative to the device. What I'd need is to compensate the device rotation so that I get the same 3 values, regardless of how the device is rotated.

我尝试与旋转矩阵相乘(我知道如何得到它)，尝试与倾角矩阵相乘等等，但没有任何效果.无论我尝试什么，当我旋转设备时，值仍然会发生变化.

I tried to multiply with the rotation matrix (I know how to get that), tried to multiply with the inclination matrix and so on, but nothing works. Regardless of what I try, still the values change when I rotate the device.

那么有人知道怎么做吗?最好使用代码，因为我读了很多东西，比如那么你必须使用旋转矩阵来补偿它"，但没有找到一个具体的工作示例.

So does anyone know how to do it right? Preferrably with code, because I read a lot of stuff like 'well then you'll have to compensate that using rotation matrix' but did not find a single concrete, working example.

推荐答案

这样做

private static final int TEST_GRAV = Sensor.TYPE_ACCELEROMETER;
private static final int TEST_MAG = Sensor.TYPE_MAGNETIC_FIELD;
private final float alpha = (float) 0.8;
private float gravity[] = new float[3];
private float magnetic[] = new float[3];

public void onSensorChanged(SensorEvent event) {
    Sensor sensor = event.sensor;
    if (sensor.getType() == TEST_GRAV) {
            // Isolate the force of gravity with the low-pass filter.
              gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];
              gravity[1] = alpha * gravity[1] + (1 - alpha) * event.values[1];
              gravity[2] = alpha * gravity[2] + (1 - alpha) * event.values[2];
    } else if (sensor.getType() == TEST_MAG) {

            magnetic[0] = event.values[0];
            magnetic[1] = event.values[1];
            magnetic[2] = event.values[2];

            float[] R = new float[9];
            float[] I = new float[9];
            SensorManager.getRotationMatrix(R, I, gravity, magnetic);
            float [] A_D = event.values.clone();
            float [] A_W = new float[3];
            A_W[0] = R[0] * A_D[0] + R[1] * A_D[1] + R[2] * A_D[2];
            A_W[1] = R[3] * A_D[0] + R[4] * A_D[1] + R[5] * A_D[2];
            A_W[2] = R[6] * A_D[0] + R[7] * A_D[1] + R[8] * A_D[2];

            Log.d("Field","
X :"+A_W[0]+"
Y :"+A_W[1]+"
Z :"+A_W[2]);

        }
    }

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