如何通过道路找到两个地方之间的距离？我应该使用Json吗？如何从地图上提取距离并将其显示在textview上？

Question

我找到了两个地理位置点，并得到了两个点之间的距离。但是它显示的是最短的距离。我想通过公路找到距离。如何使用它？我对JSON不太了解？终点如何通过道路找到距离？？？

    import java.util.List;
    import java.util.Locale;

    import android.app.Activity;
    import android.content.Context;
    import android.content.Intent;
    import android.location.Address;
    import android.location.Geocoder;
    import android.location.Location;
    import android.net.Uri;
    import android.os.Bundle;
    import android.util.FloatMath;
    import android.util.Log;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.TextView;
    import android.widget.Toast;

    public class WhereDoYouLive extends Activity {
        /** Called when the activity is first created. */


        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);  // Set up GUI

    final EditText addressfield = (EditText) findViewById(R.id.address);  // Reference edit field
            final EditText addressfield2 = (EditText) findViewById(R.id.secaddress);
            final Button launchmapbtn = (Button) findViewById(R.id.launchmap);  // Reference search button
          final TextView lat=(TextView)findViewById(R.id.lat);
          final TextView lon=(TextView)findViewById(R.id.lon);
          final TextView lat2=(TextView)findViewById(R.id.lat2);
          final TextView lon2=(TextView)findViewById(R.id.lon2);
          final TextView result=(TextView)findViewById(R.id.res);
           final double latitude = 0 ;
          final double longitude = 0;
          final double latitude2 = 0;
          final double longitude2 = 0;


            launchmapbtn.setOnClickListener(new OnClickListener(){  
                    public void onClick(View v) { 
                        // List<Address> addresses=null;
                         String aa=addressfield.getText().toString();
                         String bb=addressfield2.getText().toString();
                         Geocoder geocoder = new Geocoder(getApplicationContext(),Locale.getDefault()); 


                        try {


    List<Address> addresses;
    addresses = geocoder.getFromLocationName(aa, 1);

    if(addresses.size() > 0) {
        double latitude= addresses.get(0).getLatitude();
        double longitude= addresses.get(0).getLongitude();
       String lt=Double.toString(latitude);
        String lg=Double.toString(longitude);
        lat.setText(lt);
        lon.setText(lg);
    }

                        } catch (Exception e){


                        }   



                        try {


                            List<Address> addresses2 ;
                            addresses2 = geocoder.getFromLocationName(bb, 1);

                            if(addresses2.size() > 0) {
                                double latitude2= addresses2.get(0).getLatitude();
                                double longitude2= addresses2.get(0).getLongitude();
                                String lt2=Double.toString(latitude2);
                                String lg2=Double.toString(longitude2);
                                lat2.setText(lt2);
                                lon2.setText(lg2);

                                double finaldistance=distFrom ( latitude, longitude, latitude2, longitude2 );
                                String finaldistance1=Double.toString(finaldistance)    ;
                                result.setText(finaldistance1);


                            }

                            } catch (Exception e) {
                            // TODO: handle exception
                        }



                        }
            });
        }


       public static double distFrom(double lat1, double lng1, double lat2, double lng2) {
            double EARTH_RADIUS = 6371.00

; 

        double earthRadius = EARTH_RADIUS;
        double dLat = Math.toRadians(lat2-lat1);
        double dLng = Math.toRadians(lng2-lng1);



        double a = Math.sin(dLat/2) * Math.sin(dLat/2) +
                Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) *
                Math.sin(dLng/2) * Math.sin(dLng/2);
        double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
        double dist = earthRadius * c;

        return new Float(dist).floatValue();


    }


}

这是xml文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >

    <TextView 
        android:id="@+id/lat" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" />

      <TextView 
        android:id="@+id/lon" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" />

      <TextView 
        android:id="@+id/lat2" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" />

      <TextView 
        android:id="@+id/lon2" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" />
      <TextView 
        android:id="@+id/res" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" />


<EditText 
android:text="Enter your address" 
android:id="@+id/address" 
android:layout_width="fill_parent" 
android:layout_height="wrap_content">
</EditText>

<EditText 
android:text="Enter your secondaddress" 
android:id="@+id/secaddress" 
android:layout_width="fill_parent" 
android:layout_height="wrap_content">
</EditText>

<Button 
android:text="Search" 
android:id="@+id/launchmap" 
android:layout_width="150px" 
android:layout_height="wrap_content">
</Button>

</LinearLayout>

这是使用google maps查找距离的链接。只需给出坐标即可。 Google地图测距仪

我试过的座标分别是8.495,76.929167和8.5580957,76.8807437，但我得到的答案是8565.2763671。我不知道它的单位是多少（即以公里还是英里为单位）。但是正确的答案应该是11.5公里或11.7公里我如何获得正确答案？