AR app using the compass to rotate the camera problem

Android Processing

planktron

AR app using the compass to rotate the camera problem

in Android Processing • 2 years ago

Hi guys!

I have been trying to make the camera work with the data from the magnetic field sensor in the phone. It sort of works but orientation of the camera is messed up. The final outcome should be something similar to first-person camera (google sky map for example). I've tried to manipulate the sensor data but no luck so far :(

Any ideas anyone? Has anybody tried this? Maybe to use some other library?

The code I've been tweaking:

// android_sensorData
// Eric Pavey - 2010-10-10
// http://www.akeric.com
//
// Query the phone's accelerometer and magnetic field data, display on screen.
// Made with Android 2.1, Processing 1.2
//-----------------------------------------------------------------------------------------
// Imports required for sensor usage:
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorManager;
import android.hardware.SensorEventListener;
import android.os.Bundle;
import android.view.WindowManager;
//-----------------------------------------------------------------------------------------
// Screen Data:
float sw, sh;
// Font Data:
String[] fontList;
PFont androidFont;
// Setup variables for the SensorManager, the SensorEventListeners,
// the Sensors, and the arrays to hold the resultant sensor values:
SensorManager mSensorManager;
MySensorEventListener accSensorEventListener;
MySensorEventListener magSensorEventListener;
Sensor acc_sensor;
float[] acc_values;
Sensor mag_sensor;
float[] mag_values;
float SmoothingConst = 0.05f;
//-----------------------------------------------------------------------------------------
void setup() {
size(screenWidth, screenHeight, P3D);
// Set this so the sketch won't reset as the phone is rotated:
orientation(PORTRAIT);
// Setup Fonts:
fontList = PFont.list();
androidFont = createFont(fontList[0], 16, true);
textFont(androidFont);
}
//-----------------------------------------------------------------------------------------
void draw() {
camera(0, 0, 0, mag_values[0], mag_values[1], 0, 0.0, 1.0, 0.0);
background(196, 236, 255);
lights();
beginShape();
vertex(-400, 400,-100);
vertex(-400, -400, -100);
vertex(400,-400, -100);
vertex(400,400,-100);
endShape(CLOSE);
}
//-----------------------------------------------------------------------------------------
// Override the parent (super) Activity class:
// States onCreate(), onStart(), and onStop() aren't called by the sketch. Processing is entered at
// the 'onResume()' state, and exits at the 'onPause()' state, so just override them:
void onResume() {
super.onResume();
println("RESUMED! (Sketch Entered...)");
// Build our SensorManager:
mSensorManager = (SensorManager)getSystemService(Context.SENSOR_SERVICE);
// Build a SensorEventListener for each type of sensor:
magSensorEventListener = new MySensorEventListener();
accSensorEventListener = new MySensorEventListener();
// Get each of our Sensors:
acc_sensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mag_sensor = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
// Register the SensorEventListeners with their Sensor, and their SensorManager:
mSensorManager.registerListener(accSensorEventListener, acc_sensor, SensorManager.SENSOR_DELAY_GAME);
mSensorManager.registerListener(magSensorEventListener, mag_sensor, SensorManager.SENSOR_DELAY_GAME);
}
void onPause() {
// Unregister all of our SensorEventListeners upon exit:
mSensorManager.unregisterListener(accSensorEventListener);
mSensorManager.unregisterListener(magSensorEventListener);
println("PAUSED! (Sketch Exited...)");
super.onPause();
}
//-----------------------------------------------------------------------------------------
// Setup our SensorEventListener
class MySensorEventListener implements SensorEventListener {
void onSensorChanged(SensorEvent event) {
int eventType = event.sensor.getType();
if (eventType == Sensor.TYPE_ACCELEROMETER) {
acc_values = LowPass( event.values, acc_values );
}
else if (eventType == Sensor.TYPE_MAGNETIC_FIELD) {
mag_values = event.values;
}
}
void onAccuracyChanged(Sensor sensor, int accuracy) {
// do nuthin'...
}
}
float[] LowPass (float[] input, float[] output) {
if (output == null) return input;
for ( int i=0; i<input.length; i++ ) {
output[i] = output[i] + SmoothingConst * (input[i] - output[i]);
}
return output;
}
void onCreate(Bundle bundle) {
super.onCreate(bundle);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
}

Replies(5)

Jesse Sco..

Re: AR app using the compass to rotate the camera problem

2 years ago

Have you tried inverting the mag_values?

I started to work form Eric's same sketch with accelerometer (but skipped the magnetics), but found that I needed to invert the values to get the accelerometer to feel correct (ie. 10-acc_values[0] ...)

nimamotam..

Re: AR app using the compass to rotate the camera problem

2 years ago

I've been hoping to do this too!

Basically, it involves complex math that is beyond my comprehension.

You can get a compass using 2 degrees of information by using:

float CompassDegree = degree (atan2 (YvaluefromMagnet, XvaluefromMagnet));

but the device has to be flat on the table, not very practical. Haven't figured out the math involved for true compassing.

planktron

Re: AR app using the compass to rotate the camera problem

2 years ago

Actually by inverting some of the values makes the sketch work pretty close, but the readings are somewhat off. I've tried to search what has been done in native Java 3D compass apps but haven't found any helpful code, so it could be ported to Processing (if there is at all something similar in native apps :S).

nimamotam..

Re: Re: AR app using the compass to rotate the camera problem

2 years ago

Which sensor values are you inverting?

this may be a dumb question, but how many degrees is it off, because the magnetometer will point to magnetic north, not true north. So maybe it's actually right because it's pointing to magnetic north.

I've been reading this page for background material: http://www.movable-type.co.uk/scripts/latlong.html

I was able to make a 2D compass based on what I;ve learned, but again, the device needs to be flat on the Z axis to use it properly :(

planktron

Re: AR app using the compass to rotate the camera problem

2 years ago

My idea was to use the magnetic north as a anchor point for the camera's "center of the scene" point ( camera()). So the eye of the camera would stay still and the point produced by the magnetic field would fly around the eye and point to the right direction producing the effect of Layar for example. So there is no need to calculate the degree for compass.

Code works fine when I point the phone in front, up or down but it doesn't work when I tilt the phone sideways or change the direction on horizontal plane. Actually when I try to tilt the phone sideway the square I have drawn rotates horizontally.

The code so far in draw():

void draw() {
camera(0, 0, 0, 10-mag_values[0], 10-mag_values[1], mag_values[2], 0.0, 0.0, 1.0);
background(196, 236, 255);
lights();
beginShape();
vertex(-400, 400,-100);
vertex(-400, -400, -100);
vertex(400,-400, -100);
vertex(400,400,-100);
endShape(CLOSE);
}

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