I'm working on Trilateration to find position of unknown location, to find distance i use path-loss with constant is 2 like in the articles, i'm using 2 phone and one laptop as the transmitter and reference. Here's the code :
distance1 = (double) Math.pow(10, ((rssi.get(k)-rssi1.get(a))/10*2));
rssi is rssi value 1m from reference and rssi1 is unknown location rssi.
And here's Trilateration code which formula is from This :
double r1 = Math.pow(distance1,2 );
double r2 = Math.pow(distance2,2 );
double r3 = Math.pow(distance3,2 );
double x1 = Math.pow(X1,2 );
double x2 = Math.pow(X2,2 );
double x3 = Math.pow(X3,2 );
double y1 = Math.pow(Y1,2 );
double y2 = Math.pow(Y2,2 );
double y3 = Math.pow(Y3,2 );
double A = r1 - r2 - x1+x2 - y1+y2;
double B = r2 - r3 - x2+x3 - y2+y3;
double C = ((-2*X1)+(2*X2));
double D = ((-2*Y1)+(2*Y2));
double E = ((-2*X2)+(2*X3));
double F = ((-2*Y2)+(2*Y3));
double x0 = (((A*F)-(B*D))/((F*C)-(E*D)));
double y0 = (((A*E)-(C*B))/((D*E)-(C*F)));
Log.v("x", String.valueOf(x0));
Log.v("y", String.valueOf(y0));
at first it gives quite accurate result but later the result is not change or even have a big error. I wonder why the result is not change is it because when do new calculation the previous result is not cleared or what? or there's some error in my code? I'm a little bit confuse, because there's more than one way to do trilateration from many source, like this:
double delta = 4*((X1-X2)*(Y1-Y3)-(X1-X3)*(Y1-Y2));
double x0 = (1/delta) * ((2*A*(y1-y3))-(2*B*(y1-y2)));
double y0 = (1/delta) * ((2*B*(x1-x2))-(2*A*(x1-x3)));
It's using delta to calculate which i don't understand where's it come from. I understand the first code which it's a linear equation. Is my constant to calculate distance is wrong? is there any code to do Trilateration with explanation of the formula? Also i trying to expanding time for receiving rssi signal and than average it, but the result is still bad.
Full code:
ArrayList<String> buildings;
DatabaseHelper db;
ArrayAdapter<String> arrayAdapter;
ArrayList<PositionData> positionsData;
String building;
TextView result;
TextView result2;
TextView result3;
Button locate;
public void onCreate(Bundle saveInstanceState) {
super.onCreate(saveInstanceState);
setContentView(R.layout.locate_wifi);
db = new DatabaseHelper(this);
buildings = db.getBuildings_wifi();
locate = (Button) findViewById(R.id.locate);
result = (TextView) findViewById(R.id.result);
result2 = (TextView) findViewById(R.id.result2);
result3 = (TextView) findViewById(R.id.result3);
arrayAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, buildings);
locate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Intent intent = new Intent(getApplicationContext(), Scan.class);
intent.putExtra("isLearning", false);
startActivityForResult(intent,0);
}
});
arrayAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, buildings);
// Set The Adapter
if (buildings.size()==0) {
Toast.makeText(this, "No building data available.", Toast.LENGTH_LONG).show();
locate.setEnabled(false);
}
else{
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setCancelable(false);
builder.setTitle("Choose building");
builder.setAdapter(arrayAdapter, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// the user clicked on colors[which]
building = buildings.get(which);
}
});
builder.show();
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode,
Intent intent) {
// TODO Auto-generated method stub
if(resultCode==RESULT_OK){
PositionData positionData = (PositionData) intent
.getSerializableExtra("PositionData");
positionsData=db.getWifiPositions(building);
ArrayList<Router> wifis = db.getFriendlyWifis(building);
HashMap<String, Double> rssi = positionData.getValues();
HashMap<String, Double> rssi1 = positionsData.get(0).getValues();
HashMap<String, Double> rssi2 = positionsData.get(1).getValues();
HashMap<String, Double> rssi3 = positionsData.get(2).getValues();
double X1 = positionsData.get(0).getX();
Double X2 = positionsData.get(1).getX();
Double X3 = positionsData.get(2).getX();
Double Y1 = positionsData.get(0).getY();
Double Y2 = positionsData.get(1).getY();
Double Y3 = positionsData.get(2).getY();
double distance1 = 0;
double distance2 = 0;
double distance3 = 0;
for (String k : rssi.keySet()) {
for (String a : rssi1.keySet()) {
if (k.equals(a)) {
Log.d("value",((Math.pow(10, ((rssi.get(k)-rssi1.get(a))/10*2))))+"");
distance1 = (double) Math.pow(10, ((rssi.get(k)-rssi1.get(a))/10*2));
}
}
for (String b : rssi2.keySet()) {
if (k.equals(b)) {
Log.d("value2",((Math.pow(10, ((rssi.get(k)-rssi2.get(b))/10*2))))+"");
distance2 = (double) Math.pow(10, ((rssi.get(k)-rssi2.get(b))/10*2));
}
}
for (String c : rssi3.keySet()) {
if (k.equals(c)) {
Log.d("value3",((Math.pow(10, ((rssi.get(k)-rssi3.get(c))/10*2))))+"");
distance3 = (double) Math.pow(10, ((rssi.get(k)-rssi3.get(c))/10*2));
}
}
}
double r1 = Math.pow(distance1,2 );
double r2 = Math.pow(distance2,2 );
double r3 = Math.pow(distance3,2 );
double x1 = Math.pow(X1,2 );
double x2 = Math.pow(X2,2 );
double x3 = Math.pow(X3,2 );
double y1 = Math.pow(Y1,2 );
double y2 = Math.pow(Y2,2 );
double y3 = Math.pow(Y3,2 );
double A = r1 - r2 - x1+x2 - y1+y2;
double B = r2 - r3 - x2+x3 - y2+y3;
//double delta = 4*((X1-X2)*(Y1-Y3)-(X1-X3)*(Y1-Y2));
//double x0 = (1/delta) * ((2*A*(y1-y3))-(2*B*(y1-y2)));
//double y0 = (1/delta) * ((2*B*(x1-x2))-(2*A*(x1-x3)));
double C = ((-2*X1)+(2*X2));
double D = ((-2*Y1)+(2*Y2));
double E = ((-2*X2)+(2*X3));
double F = ((-2*Y2)+(2*Y3));
double x0 = (((A*F)-(B*D))/((F*C)-(E*D)));
double y0 = (((A*E)-(C*B))/((D*E)-(C*F)));
Log.v("x", String.valueOf(x0));
Log.v("y", String.valueOf(y0));
result.setText("X: "+ x0);
result2.setText("Y: "+ y0);
super.onActivityResult(requestCode, resultCode, intent);
}
}
public class CustomOnItemSelectedListener implements
AdapterView.OnItemSelectedListener {
public void onItemSelected(AdapterView<?> parent, View view, int pos,
long id) {
building = parent.getItemAtPosition(pos).toString();
locate.setEnabled(true);
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
locate.setEnabled(false);
}
}
}
