android maps auto-rotate

问题:

If you open the Google maps app, there is a button on the top right of the screen that you can press to center the map on your current location. The button's icon then changes. If you press the same button again, the map auto-rotates based on your compass heading. In other words, the map becomes egocentric (as opposed to allocentric AKA north always up).

Google recently launched maps API V2 for Android and I certainly like it more than the old one. By default, android maps V2 will include the "center on location" button. However, pressing it more than once does not enable auto-rotation; it merely tries to center the map on your location again.

Does anyone know how I can auto-rotate the map using maps API v2 just like the google maps app does? Will I have to implement this functionality myself or is it in the API and i'm just not seeing it? I appreciate all help.

回答1:

Ok here's how I think it should be done a year later. Please correct me if you spot any issues.

Most of the following code deals with a discrepancy between coordinate systems. I'm using a rotation vector sensor. From the docs: Y is tangential to the ground at the device's current location and points towards magnetic north. Bearing in google maps, on the other hand, seems to point to true north. this page shows how the conversion is done

1) get the current declination from your current GPS location

@Override
public void onLocationChanged(Location location) {
    GeomagneticField field = new GeomagneticField(
            (float)location.getLatitude(),
            (float)location.getLongitude(),
            (float)location.getAltitude(),
            System.currentTimeMillis()
        );

    // getDeclination returns degrees
    mDeclination = field.getDeclination();
} 

2) calculate bearing from declination and magnetic north

    @Override
public void onSensorChanged(SensorEvent event) {
    if(event.sensor.getType() == Sensor.TYPE_ROTATION_VECTOR) {
        SensorManager.getRotationMatrixFromVector(
                mRotationMatrix , event.values);
        float[] orientation = new float[3];
        SensorManager.getOrientation(mRotationMatrix, orientation);
        float bearing = Math.toDegrees(orientation[0]) + mDeclination;
        updateCamera(bearing);  
    }
}

3) update maps

private void updateCamera(float bearing) {
    CameraPosition oldPos = mMap.getCameraPosition();

    CameraPosition pos = CameraPosition.builder(oldPos).bearing(bearing).build();
            mMap.moveCamera(CameraUpdateFactory.newCameraPosition(pos));
}

回答2:

I have successfully implemented aleph_null solution and here I will add some details that are not mentioned in the accepted solution:

For the above solution to work you need to implement android.hardware.SensorEventListener interface.

You need also to register to the SensorEventListener in your onResume and onPause methods as follow:

@Override
    protected void onResume() {
     super.onResume();
     mSensorManager.registerListener(this,
             mRotVectSensor,
             SensorManager.SENSOR_STATUS_ACCURACY_LOW);
    }

@Override
protected void onPause() {
    // unregister listener
    super.onPause();
    mSensorManager.unregisterListener(this);
}

Note to "@Bytecode": To avoid flickering, use low value for the sampling period, something like SensorManager.SENSOR_STATUS_ACCURACY_LOW.

I have noticed also that the sensor sends sometime more data than the device can handle and as a result, the map camera starts to move in a strange way!

To control the amount of data handled by onSensorChanged, I suggest the following implementation:

@Override
public void onSensorChanged(SensorEvent event) {
    if(event.sensor.getType() == Sensor.TYPE_ROTATION_VECTOR) {
        SensorManager.getRotationMatrixFromVector(
                mRotationMatrix, event.values);
        float[] orientation = new float[3];
        SensorManager.getOrientation(mRotationMatrix, orientation);
        if (Math.abs(Math.toDegrees(orientation[0]) - angle) > 0.8) {
            float bearing = (float) Math.toDegrees(orientation[0]) + mDeclination;
            updateCamera(bearing);
        }
        angle = Math.toDegrees(orientation[0]);
    }
}

回答3:

It is possible by registering your application with Sensor Listener for Orientation and getting the angle relative to true north inside onSensorChanged and update camera accordingly. Angle can be used for bearing. The following code can be used:

Instead of using Sensor.TYPE_ORIENTATION try using getOrinetation api. Sensor.TYPE_ORIENTATION
has been deprecated.

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
    if (sensorManager != null)
        sensorManager.registerListener(this,
                sensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION),
                SensorManager.SENSOR_DELAY_GAME);
}

public void onSensorChanged(SensorEvent event) {

    float degree = Math.round(event.values[0]);

    Log.d(TAG, "Degree ---------- " + degree);

    updateCamera(degree);

}

private void updateCamera(float bearing) {
    CameraPosition oldPos = googleMap.getCameraPosition();

    CameraPosition pos = CameraPosition.builder(oldPos).bearing(bearing)
            .build();

    googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(pos));

}

回答4:

Sorry, you'll have to implement it yourself with the sensor manager and the camera

if those functions were available to the map api V2 they would certainly be either on the GoogleMap or the UiSettings