Android获得相对于地平线的角度

Question

I've been working on trying to get the angle of an Android device (which I assume is being held with the back of the device parallel to the ground) relative to the horizon. I've been using the Rotation Vector sensor but the values I'm getting are too ambiguous to be of use.

For example, when I tilt the device to the right (from the position stated above, with little to no tilt in other directions), I get the following values:

X = 0.4
Y = -0.4
Z = -0.06

For similar tests (eg tilt to the left, tilt so the top of the phone faces downwards/upwards), I get equally confusing results.

To be very specific about what I expect: I expected that I would see a significant change in one axis (as I'm only rotating in one axis) and minimal to no change on the others. This way, I could figure out if a person was tilting left, right, up, down, or a combination (eg right/down, left/up, etc.). With these values, it's near impossible for me to ascertain this data.

I tagged this question with the math tag as it may be that I need to use the Rotation vector matrix or do some other mathematical transformation in order to get the values in the format I need them in. If that is the case, I would appreciate guidance as to what algorithms/formulae I need, hence the tag.

Below is my prototype code if you'd like to test for yourself (this was run on a Nexus 5 running Android 5.0.1):

MainActivity.xml:

<TextView
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:id="@+id/xAxis"
    android:text="Medium Text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="Medium Text"
    android:id="@+id/yAxis"
    android:layout_gravity="center" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="Medium Text"
    android:id="@+id/zAxis"
    android:layout_gravity="center" />
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/dir"/>
<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/calibrate"
    android:text="Calibrate"/>

</LinearLayout>

MainActivity.java:

package com.example.rotationvectortest;

import android.app.Activity;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.text.DecimalFormat;


public class MainActivity extends Activity implements SensorEventListener     {

private SensorManager sensorManager;
private Sensor sensor;
private TextView xAxisView;
private TextView yAxisView;
private TextView zAxisView;
private TextView mDir;
private Button mCalibrate;

float x = 0;
float y = 0;
float z = 0;

boolean cal = false;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    xAxisView = (TextView) findViewById(R.id.xAxis);
    yAxisView = (TextView) findViewById(R.id.yAxis);
    zAxisView = (TextView) findViewById(R.id.zAxis);
    mDir = (TextView) findViewById(R.id.dir);
    mCalibrate = (Button) findViewById(R.id.calibrate);
    mCalibrate.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            cal = true;
        }
    });
    xAxisView.setText("X = 0.0");
    yAxisView.setText("Y = 0.0");
    zAxisView.setText("Z = 0.0");
    sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
    sensor = sensorManager.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR);
    sensorManager.registerListener(this, sensor, 50000);

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@Override
public void onSensorChanged(SensorEvent event) {

    if (cal) {
        x = event.values[0];
        y = event.values[1];
        z = event.values[2];
        cal = false;
    }

    DecimalFormat format = new DecimalFormat("#.##");
    xAxisView.setText("X = " + format.format(event.values[0] - x));
    yAxisView.setText("Y = " + format.format(event.values[1] - y));
    zAxisView.setText("Z = " + format.format(event.values[2] - z));

}

@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {

}
}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.rotationvectortest" >
<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:screenOrientation="portrait">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

Answer 1

So the values you get from the rotation vector are are based off of internal coordinates, and are essentially useless when it comes to understanding the devices' angle relative to the ground (or some other fixed point in the world).

If you pass the data provided to you by the rotation vector sensor in SensorManager 's getRotationMatrixFromVector() call, the first three values are the azimuth, pitch, and roll (ie angles in the x,y, and z axes respectively) of the device.