我正在尝试制作一个每隔5秒钟就能获得一个位置的车速表应用程序。计算距离并获得用户速度，但我的初始数据首先显示高值，甚至没有移动手机，而是一种随机值。请检查我的代码。
MainActivity.java
public class MainActivity extends Activity {
private static final int REQUEST_CODE_PERMISSION = 2;
String mPermission = Manifest.permission.ACCESS_FINE_LOCATION;
TextView tvRunning, tvMax;
int maxv = 0;
// GPSTracker class
GPSTracker gps;
GPSTracker GPSTrackerBefore = new GPSTracker(MainActivity.this);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tvRunning = (TextView) findViewById(R.id.tvRunnung);
tvMax = (TextView) fin
dViewById(R.id.tvMax);
try {
if (ActivityCompat.checkSelfPermission(this, mPermission)
!= MockPackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this, new String[]{mPermission},
REQUEST_CODE_PERMISSION);
// If any permission above not allowed by user, this condition will
//execute every time,else your else part will work
}
} catch (Exception e) {
e.printStackTrace();
}
//----------------initializing the first gps----------------//
if(GPSTrackerBefore.canGetLocation){
GPSTrackerBefore.getLocation();
}
final Handler ha = new Handler();
ha.postDelayed(new Runnable() {
@Override
public void run() {
//call function
[enter image description here][1]
gps = new GPSTracker(MainActivity.this);
// check if GPS enabled
if (gps.canGetLocation()) {
double lon2 = gps.getLongitude(), lat2 = gps.getLatitude();
double lon1 = GPSTrackerBefore.getLongitude(), lat1 = GPSTrackerBefore.getLatitude();
int R = 6371; // km
double x = (lon2 - lon1) * Math.cos((lat1 + lat2) / 2);
double y = (lat2 - lat1);
int d = (int) Math.sqrt(x * x + y * y) * R;
int v=d/5; //this is the velocity divided by interval time
Toast.makeText(getApplicationContext(), String.valueOf(v), Toast.LENGTH_SHORT).show();
// Toast.makeText(getApplicationContext(),
// gps.getLatitude()+"||"+gps.getLongitude()+
// "\n"+GPSTrackerBefore.getLatitude()+"||"+GPSTrackerBefore.getLongitude(),
// Toast.LENGTH_SHORT).show();
GPSTrackerBefore = gps;
tvRunning.setText(String.valueOf(v));
if (v > maxv) {
maxv = v;
tvMax.setText(String.valueOf(maxv));
}
} else {
// can't get location
// GPS or Network is not enabled
// Ask user to enable GPS/network in settings
gps.showSettingsAlert();
}
ha.postDelayed(this, 5000);
}
}, 5000);
}
}
GPSTracker.java
package bytebiters.com.speedo;
public class GPSTracker extends Service implements LocationListener {
private final Context mContext;
// flag for GPS status
boolean isGPSEnabled = false;
// flag for network status
boolean isNetworkEnabled = false;
// flag for GPS status
boolean canGetLocation = false;
Location location; // location
double latitude; // latitude
double longitude; // longitude
// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 1; // 1 meters
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 3000 ; // 1 sec
// Declaring a Location Manager
protected LocationManager locationManager;
public GPSTracker(Context context) {
this.mContext = context;
getLocation();
}
public Location getLocation() {
try {
locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE);
// getting GPS status
isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
// getting network status
isNetworkEnabled = locationManager
.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if (!isGPSEnabled && !isNetworkEnabled) {
// no network provider is enabled
} else {
this.canGetLocation = true;
// First get location from Network Provider
if (isNetworkEnabled) {
locationManager.requestLocationUpdates(
LocationManager.NETWORK_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("Network", "Network");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
// if GPS Enabled get lat/long using GPS Services
if (isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("GPS Enabled", "GPS Enabled");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
return location;
}
/**
* Stop using GPS listener
* Calling this function will stop using GPS in your app
* */
public void stopUsingGPS(){
if(locationManager != null){
locationManager.removeUpdates(GPSTracker.this);
}
}
/**
* Function to get latitude
* */
public double getLatitude(){
if(location != null){
latitude = location.getLatitude();
}
// return latitude
return latitude;
}
/**
* Function to get longitude
* */
public double getLongitude(){
if(location != null){
longitude = location.getLongitude();
}
// return longitude
return longitude;
}
/**
* Function to check GPS/wifi enabled
* @return boolean
* */
public boolean canGetLocation() {
return this.canGetLocation;
}
/**
* Function to show settings alert dialog
* On pressing Settings button will lauch Settings Options
* */
public void showSettingsAlert(){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
// Setting Dialog Title
alertDialog.setTitle("GPS is settings");
// Setting Dialog Message
alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");
// On pressing Settings button
alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
mContext.startActivity(intent);
}
});
// on pressing cancel button
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
// Showing Alert Message
alertDialog.show();
}
@Override
public void onLocationChanged(Location location) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public IBinder onBind(Intent arg0) {
return null;
}
}
答案 0 :(得分：0)
在GPSTracker中，如果没有可用的位置，尝试读取纬度或经度将返回0。在尝试使用方法估算速度之前，您需要多个读数。
除了代码，GPS坐标本质上是有噪声的（位置不确切）。由位置估计中的噪声引起的速度测量总是存在误差。有更复杂的方法可用于估计噪声测量的速度和位置，例如Kalman Filter。