I am using Sensortag CC2541 (connected to Nexus phone)
I am using the Magnetometer of this sensor to make a simple compass. I am using the following equations to find North, South, West, and East.
Direction (y>0) = 90 - [arcTAN(x/y)]*180/pi
Direction (y<0) = 270 - [arcTAN(x/y)]*180/pi
Direction (y=0, x<0) = 180.0
Direction (y=0, x>0) = 0.0
Here's the code i'm using in my updateMagnetometer method
@Override
public void onUpdateMagnetometer(SensorTagManager mgr, Point3D b) {
super.onUpdateMagnetometer(mgr, b);
double m=0;
if(b.x < 0.0 && (b.y < 0.01 && b.y > 0.0))
m = 180;
else if(b.x > 0.0 && (b.y < 0.01 && b.y > 0.0))
m = 0;
else if(b.y > 0.0)
m = 90 - (Math.atan(b.x/b.y))*(180/Math.PI);
else if(b.y < 0.0)
m = 270 - (Math.atan(b.x/b.y))*(180/Math.PI);
final float rot = (float) m;
runOnUiThread(new Runnable() {
@Override
public void run() {
pointer.setRotation(-rot); //pointer is the image of my compass
}
});
}
But when I run it, the compass is always stuck between North and West NO MATTER how much I move, rotate, or change the position of the sensor.
Any mistakes I might be doing?
And also, I have looked a lot on the internet for making compass help. But I can't find anything. Any coding tips, pseudo code, or hint to make compass using magnetometer, accelerometer, and/or gyroscope???
Extra info
So this is in my main class. These methods are called every x seconds to update the readings.
PS: my sensor has 2 buttons (right and left)
mStManager.enableSensor(Sensor.MAGNETOMETER,MAGNETOMETER_UPDATE_PERIOD);
mStManager.enableSensor(Sensor.ACCELEROMETER,MAGNETOMETER_UPDATE_PERIOD);
@Override
public void onUpdateAmbientTemperature(SensorTagManager mgr, double temp) {
super.onUpdateAmbientTemperature(mgr, temp);
}
@Override
public void onUpdateAccelerometer(SensorTagManager mgr, Point3D acc) {
super.onUpdateAccelerometer(mgr, acc);
}
@Override
public void onUpdateBarometer(SensorTagManager mgr, double pressure, double height) {
super.onUpdateBarometer(mgr, pressure, height);
}
@Override
public void onUpdateGyroscope(SensorTagManager mgr, Point3D ang) {
super.onUpdateGyroscope(mgr, ang);
}
@Override
public void onUpdateHumidity(SensorTagManager mgr, double rh) {
super.onUpdateHumidity(mgr, rh);
}
@Override
public void onUpdateInfraredTemperature(SensorTagManager mgr, double temp) {
super.onUpdateInfraredTemperature(mgr, temp);
}
@Override
public void onUpdateKeys(SensorTagManager mgr, boolean left, boolean right) {
super.onUpdateKeys(mgr, left, right);
if (right) {
mgr.calibrateMagnetometer();
}
}
@Override
public void onUpdateMagnetometer(SensorTagManager mgr, Point3D b) {
super.onUpdateMagnetometer(mgr, b);
}
}
So basically in the onUpdateMagnetometer method, the b contains my reading. It is of class Point3D which is shown below
public class Point3D {
public double x, y, z;
public Point3D(double x, double y, double z) {
this.x = x;
this.y = y;
this.z = z;
}
public double norm() {
return Math.sqrt(x*x + y*y + z*z);
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
long temp;
temp = Double.doubleToLongBits(x);
result = prime * result + (int) (temp ^ (temp >>> 32));
temp = Double.doubleToLongBits(y);
result = prime * result + (int) (temp ^ (temp >>> 32));
temp = Double.doubleToLongBits(z);
result = prime * result + (int) (temp ^ (temp >>> 32));
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Point3D other = (Point3D) obj;
if (Double.doubleToLongBits(x) != Double.doubleToLongBits(other.x))
return false;
if (Double.doubleToLongBits(y) != Double.doubleToLongBits(other.y))
return false;
if (Double.doubleToLongBits(z) != Double.doubleToLongBits(other.z))
return false;
return true;
}
public String toString() {
return "[" + this.x + ", " + this.y + ", " + this.z + "]";
}
}
One problem you have is that you're handling the 3D magnetometer as a 2D sensor. It isn't.
One way to do this is to use data from both the magnetometer AND the accelerometer:
That final value represents the device's rotation around a vector pointed towards the center of the earth, which is exactly what you want for a compass. Using THAT value, you can then calculate the location of west, east, and south.
The code would look something like this: (ignoring the setup of the sensors)
// globals
private float[] gravityData = new float[3];
private float[] geomagneticData = new float[3];
private boolean hasGravityData = false;
private boolean hasGeomagneticData = false;
private double rotationInDegrees;
@Override
public void onSensorChanged(SensorEvent event) {
switch (event.sensor.getType()){
case Sensor.TYPE_ACCELEROMETER:
System.arraycopy(event.values, 0, gravityData, 0, 3);
hasGravityData = true;
break;
case Sensor.TYPE_MAGNETIC_FIELD:
System.arraycopy(event.values, 0, geomagneticData, 0, 3);
hasGeomagneticData = true;
break;
default:
return;
}
if (hasGravityData && hasGeomagneticData) {
float identityMatrix[] = new float[9];
float rotationMatrix[] = new float[9];
boolean success = SensorManager.getRotationMatrix(rotationMatrix, identityMatrix,
gravityData, geomagneticData);
if (success) {
float orientationMatrix[] = new float[3];
SensorManager.getOrientation(rotationMatrix, orientationMatrix);
float rotationInRadians = orientationMatrix[0];
rotationInDegrees = Math.toDegrees(rotationInRadians);
// do something with the rotation in degrees
}
}
}
I hope that helps!