如何跟踪用户走了多少英里？

Question

我已经在android studio中制作了一些java代码，它计算了有多少步骤，但我不确定如何计算用户行走多少英里。这是代码。

如果有人能告诉我怎么做，那将不胜感激，谢谢。

    package com.example.andyheggis.healthapp;

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements SensorEventListener {


    TextView tv_steps;

    SensorManager sensorManager;

    boolean running = false;


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



        tv_steps = (TextView) findViewById(R.id.tv_steps);

        sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
    }

    @Override
    protected void onResume() {
        super.onResume();
        running = true;
        Sensor countSensor = sensorManager.getDefaultSensor(Sensor.TYPE_STEP_COUNTER);
        if(countSensor != null) {
            sensorManager.registerListener(this, countSensor, SensorManager.SENSOR_DELAY_UI);
        }  else {
            Toast.makeText(this, "Sensor not found!", Toast.LENGTH_LONG).show();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        running = false;
        //if you unregister the hardware will stop detecting steps
        //sensorManager.unregisterListener(this);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if(running) {
            tv_steps.setText(String.valueOf(event.values[0]));
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {

    }
}