indoor navigation using smartphone with inbulit sensors

Hi,
This is the code for saving readings of accelerometer and gyroscope sensor readings from smartphone .
I need to add the sampling period between these readings for position estimation.
Please help with this code.

package com.example.sensorsave2;

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener2;
import android.hardware.SensorManager;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

@RequiresApi(api = Build.VERSION_CODES.P)
public class MainActivity extends AppCompatActivity implements SensorEventListener2 {

SensorManager manager;
Button buttonStart;
Button buttonStop;
boolean isRunning;
final String TAG = "SensorLog";
FileWriter writer;


@override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

isRunning = false;

manager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);

buttonStart = (Button)findViewById(R.id.buttonStart);
buttonStop = (Button)findViewById(R.id.buttonStop);

buttonStart.setOnTouchListener(new View.OnTouchListener() {
@override
public boolean onTouch(View view, MotionEvent motionEvent) {
buttonStart.setEnabled(false);
buttonStop.setEnabled(true);

Log.d(TAG, "Writing to " + getStorageDir());
try {
writer = new FileWriter(new File(getStorageDir(), "sensors_" + System.currentTimeMillis() + ".csv"));
} catch (IOException e) {
e.printStackTrace();
}

manager.registerListener(MainActivity.this, manager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER));
manager.registerListener(MainActivity.this, manager.getDefaultSensor(Sensor.TYPE_GYROSCOPE));
manager.registerListener(MainActivity.this, manager.getDefaultSensor(Sensor.TYPE_GYROSCOPE_UNCALIBRATED));

isRunning = true;
return true;
}
});
buttonStop.setOnTouchListener(new View.OnTouchListener() {
@RequiresApi(api = Build.VERSION_CODES.P)
@override
public boolean onTouch(View view, MotionEvent motionEvent) {
buttonStart.setEnabled(true);
buttonStop.setEnabled(false);
isRunning = false;
manager.flush(MainActivity.this);
manager.unregisterListener(MainActivity.this);
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
return true;
}
});
}

private String getStorageDir() {
return this.getExternalFilesDir(null).getAbsolutePath();
// return "/storage/emulated/0/Android/data/com.iam360.sensorlog/";
}

@override
public void onFlushCompleted(Sensor sensor) {

}

@override
public void onSensorChanged(SensorEvent evt) {
if(isRunning) {
try {
switch(evt.sensor.getType()) {
case Sensor.TYPE_ACCELEROMETER:
writer.write(String.format("%d; ACC; %f; %f; %f; %f; %f; %f\n", evt.timestamp, evt.values[0], evt.values[1], evt.values[2], 0.f, 0.f, 0.f));
break;
case Sensor.TYPE_GYROSCOPE_UNCALIBRATED:
writer.write(String.format("%d; GYRO_UN; %f; %f; %f; %f; %f; %f\n", evt.timestamp, evt.values[0], evt.values[1], evt.values[2], evt.values[3], evt.values[4], evt.values[5]));
break;
case Sensor.TYPE_GYROSCOPE:
writer.write(String.format("%d; GYRO; %f; %f; %f; %f; %f; %f\n", evt.timestamp, evt.values[0], evt.values[1], evt.values[2], 0.f, 0.f, 0.f));
break;
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

@override
public void onAccuracyChanged(Sensor sensor, int i) {

}
}