Develop Reference

Android: Issue in calculating distance using Location manager

Currently I am working on an application, where I want to calculate distance a vehicle travels. My requirement is while driving car, my Android device should calculate total distance I traveled and send this information to server. In order to do this, I used Android's location manager api, set criteria and used getBestProvider. This way we can either use GPS or Network to get latitude and longitude. The following is the code snippet of this:
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);
criteria.setPowerRequirement(Criteria.POWER_HIGH);
provider = locationManager.getBestProvider(criteria, false);
locationManager.requestLocationUpdates(provider,30000,5, this);
onLocationChanged() call back method provide latitude and longitude every time. We always store previous coordinates and when we get new coordinates we find the distance between the two using distanceBetween() api. The following is the code snippet of this:
public void onLocationChanged(Location location) {
findLatLongDistance(location);
}
private void findLatLongDistance(Location location) {
// TODO Auto-generated method stub
try{
Date date = new Date();
TimeStamp2 = sdf.format(date);
getSavedLatLong();//get lat and long from preference
Location locationB = new Location("point B");
locationB.setLatitude(location.getLatitude());
locationB.setLongitude(location.getLongitude());
Location locationA = new Location("point A");
locationA.setLatitude(prelat_val); //lat from pref locationA.setLongitude(prelong_val); //long from pref
if(prelat_val>0.0 && prelong_val>0.0){
Toast.makeText(LocationService.this,"Location Odometer Sum "+odometer_sum, Toast.LENGTH_LONG).show();
float distance2 = getDistance(prelat_val,prelong_val,location.getLatitude(),location.getLongitude());
odometer_sum = odometer_sum + (distance2/1000);
Toast.makeText(LocationService.this,"Lat "+prelat_val+"Long "+prelong_val+"Sum "+odometer_sum, Toast.LENGTH_LONG).show();
}
saveData(lat,lng,odometer_sum);
}catch(Exception e){
e.printStackTrace();
}
}
public float getDistance(double d, double e, double f, double g) {
float [] dist = new float[2];
Location.distanceBetween(d,e,f, g, dist);
return dist[0] ;
}
This is the list of issue that we face here:
The location it provide is not accurate. There is a difference of about 300-400 metres while we testing this app in 5 km distance
When the mobile is in same location for long time, it always provide different latitude and longitude. If you check above code snippet, in requestLocationUpdates(), we are setting 30 seconds time interval and 5m distance. Here what we thought is, if my mobile device move 5m distance AND if it cross 30 seconds interval, it will provide new latitude and longitude. But what really happens is, it provide coordinates every 30 seconds irrespective of device movement. I am not sure how to fix this issue.
While device is moving, how to get accurate value. Do I need to do some more things in the code?
I really spend so many hours trying various options. But I feel I am missing something here. Please help me on this. Thanks in advance..
Thanks,

Your minTime value in requestLocationUpdates() is 30seconds. Thats too long for an app that tries to calculate accurate distances. I have used locationManager.requestLocationUpdates(provider, 0, 5, locationListener);
in my code for long and I get accurate updates. Though this drains the battery very fast. So you would have to try different values to strike a balance between accuracy and battery life and see what suits your app

Altitude always 0. I cannot obtain the altitude above sea level

I get the altitude always 0. I want to obtain the altitude above sea level in Android using GPS.
My code is:
public void onLocationChanged(Location location) {
double lat = (double) (location.getLatitude());
double lng = (double) (location.getLongitude());
double alt = (double) (location.getAltitude());
latitudine = (int) (lat * 1e6);
longitudine = (int) (lng * 1e6);
altitudine = (int) (alt * 1e6);
}

Did you check if this is device specific? Are you working in an emulator?
I would at first check, if your device supports the altitude determination with:
LocationManager locationManager; LocationProvider locationProvider;
/* Get LocationManager and LocationProvider for GPS */
locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
locationProvider = locationManager.getProvider(LocationManager.GPS_PROVIDER);
/* Check if GPS LocationProvider supports altitude */
locationProvider.supportsAltitude();
If you want to know if a location has a valid altitude set, use the following:
Location location;
/* Get current location from GPS */
location = Location(LocationManager.GPS_PROVIDER);
/* Check if the requested Location has its altitude set */
location.hasAltitude();

You should check whether the location contains altitude information: before calling location.getAltitude(), just call location.hasAltitude() to know if the returned location contains this type of information.
Depending on the location provider you use (NETWORK or GPS), it may not support altitude determination. If you have an application that works with altitude, try to find which location provider it is using.
If you want to check if a particular location provider supports altitude, first call LocationManager.getProvider(SensorManager.GPS_PROVIDER) to get the LocationProvider and then call the method locationProvider.supportsAltitude().

What is more quicker is seconds ans precise provider : GPS_PROVIDER or NETWORK_PROVIDER if both are enabled?

I need to find location with android. My question is what is more quicker is seconds ans precise provider : GPS_PROVIDER or NETWORK_PROVIDER if both are enabled ? Can you tell me how long it takes to return location, I am new to this stuff and don't have any idea about time .

You can select the Criteria yo want to get the best provider, like for example if your criteria is precision:
LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
Criteria c = new Criteria();
c.setAccuracy(Criteria.ACCURACY_FINE);
final String PROVIDER = lm.getBestProvider(c, true);
Also if you want quick location, you can get the last known location with a function like this (Extracted from here):
public static Location getLastKnownLocation(LocationManager locationManager)
{
Location bestResult = null;
float bestAccuracy = 0;
long bestTime = 0;
List<String> matchingProviders = locationManager.getAllProviders();
for (String provider: matchingProviders) {
Location location = locationManager.getLastKnownLocation(provider);
if (location != null) {
float accuracy = location.getAccuracy();
long time = location.getTime();
if ((time > minTime && accuracy < bestAccuracy)) {
bestResult = location;
bestAccuracy = accuracy;
bestTime = time;
}
else if (time < minTime &&
bestAccuracy == Float.MAX_VALUE && time > bestTime){
bestResult = location;
bestTime = time;
}
}
}
return bestResult;
}

In general, GPS_PROVIDER, takes more time than NETWORK_PROVIDER considering that you are requesting for a new location. NETWORK_PROVIDER is generally quick, but GPS_PROVIDER , i can't tell you(i don't know) the exact time for this.
GPS is accurate over NETWORK.

In my case i found that NETWORK_PROVIDER is quicker than GPS_PROVIDER , It is difficult to say that
"how long it takes to return location" it's not same always...
Check this ,which i am using for retrieving the current location :
http://code.google.com/p/messesinfoandroid/source/browse/trunk/src/cef/messesinfo/maps/MyLocation.java?spec=svn12&r=12

GPS => More accurate, more time needed
Network => Less accurate, less time needed
(And, of course, you can define your preferences about this with the object Criteria)

Also GPS provider works only outdoors, Network provider works indoors as well.

Problem in getting the Latitude and Longitude value using gps at different location

I used the following code to find the longitude and latitude for my android application
public double[] getlocation() {
LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
List<String> providers = lm.getProviders(true);
Location l = null;
for (int i = 0; i < providers.size(); i++) {
l = lm.getLastKnownLocation(providers.get(i));
if (l != null)
break;
}
double[] gps = new double[2];
if (l != null) {
gps[0] = l.getLatitude();
gps[1] = l.getLongitude();
}
return gps;
}
I got the accurate or exact latitude and longitude first time when i run the application after i tried to get the new co-ordinates from one miles away from my first location but i got the same latitude and longitude.
so please can you suggest me how this problem occurs. what is the solution for this ?

.getLastKnownLocation() will be inaccurate. You need to use a LocationListener to get accurate and up to date location updates. See this link. You generally ONLY want to use getLastKnownLocation ONCE upon starting to get a quick fix, then register a LocationListener to get more accurate, constant updates.
Also be aware that sitting in your house attempting to test will not work very well. You might need to go outside and walk around some.

Refresh Latitude/Longitude or load faster

i m using lat/lng to find where is my user and calculate the distance between him and another place in the map(its lat/lng is static).In order to do this i use :
private void findloc() {
// TODO Auto-generated method stub
try{
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
provider = locationManager.getBestProvider(criteria, false);
Location location = locationManager.getLastKnownLocation(provider);
Double lat = Double.valueOf(location.getLatitude());
Double lng = Double.valueOf(location.getLongitude());
Location location2 = new Location("gps");
location2.setLatitude(35.519583);
location2.setLongitude(24.016864);
float distance = location2.distanceTo(location);
TextView sitesdistancekm = (TextView) findViewById(R.id.sitesdistancekm);
sitesdistancekm.setText("Geographical Distance : "+distance/1000+" km");
Toast.makeText(otto.this, "lat: "+lat+"\nlng: "+lng,
Toast.LENGTH_LONG).show();
}
catch(Exception e){
TextView sitesdistancekm = (TextView) findViewById(R.id.sitesdistancekm);
sitesdistancekm.setText("No GPS signal");
}
}
My problem is that sometimes the location stacks and i m getting a wrong distance .i m calling findloc() as a refresh for the menu but it doesnt changes.
public boolean onOptionsItemSelected(MenuItem item) {
findloc();
return true;
}
Is there any way to improve it?Any idea please??
EDIT
Is that gonna work?
private void findloc() {
// TODO Auto-generated method stub
try{
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
provider = locationManager.getBestProvider(criteria, false);
Location location = locationManager.getLastKnownLocation(provider);
Double lat = Double.valueOf(location.getLatitude());
Double lng = Double.valueOf(location.getLongitude());
location2 = new Location("gps");
location2.setLatitude(35.519583);
location2.setLongitude(24.016864);
float distance = location2.distanceTo(location);
TextView sitesdistancekm = (TextView) findViewById(R.id.sitesdistancekm);
sitesdistancekm.setText("Geographical Distance : "+distance/1000+" km");
Toast.makeText(otto.this, "lat: "+lat+"\nlng: "+lng,
Toast.LENGTH_LONG).show();
onLocationChanged(location);
}
catch(Exception e){
TextView sitesdistancekm = (TextView) findViewById(R.id.sitesdistancekm);
sitesdistancekm.setText("No GPS signal");
}
}
private void onLocationChanged(Location location) {
// TODO Auto-generated method st
float distance = location2.distanceTo(location);
TextView sitesdistancekm = (TextView) findViewById(R.id.sitesdistancekm);
sitesdistancekm.setText("Geographical Distance : "+distance/1000+" km");
}

I've found that getLastKnownLocation() is not as reliable as registering a location listener. See this post for good information on how to implement one.
getLastKnownLocation docs state:
Returns a Location indicating the data from the last known location
fix obtained from the given provider. This can be done without
starting the provider. Note that this location could be out-of-date,
for example if the device was turned off and moved to another
location.
For me, I use getLastKnownLocation() to get an initial location, but then register a listener for anything else.

Referring to answer by Jack, getLastKnownLocation should not be used as sole measure of location detection. You need to divide your location detection logic to several steps:
Get the best provider you have for detailed accuracy
LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
// you need to specify the criteria here
criteria.setAccuracy(Criteria.ACCURACY_FINE);
String bestProvider = lm.getBestProvider(criteria, true);
However you cannot just use last known position as is. You need to check what is the last time the this location get fixed. Depending on the sensitivity that you need, you could check for elapsed time anywhere between 30 seconds to 5 minutes.
Location locate = lm.getLastKnownLocation(bestProvider);
if(System.currentTimeMillis() - locate.getTime() < TIME_TO_EXPIRE) {
// this is a valid location, let's use this location
// as the last time the provider check is within reasonable boundary
}
If the last known update has passed your boundary of expected time, you could assume the location is too old (the user has moved to different place) and needs to be updated. The next step for you is to request for location update by calling the following
lm.requestLocationUpdates(LocationManager.GPS_PROVIDER,
MIN_TIME, MIN_DISTANCE, locationListener);
As you can see, you don't call onLocationChange manually, but rather let the provider calls the listener if MIN_TIME and MIN_DISTANCE have been exceeded.
Note that if your position hasn't changed then onLocationChanged() will not get called. If certain period has passed without onLocationChanged getting called, you can assume your last known position is the most accurate one and you should use it.
There is also chance that the onLocationChanged() doesn't get called because the provider can't get a fix for your position. In this case, optionally, you could call other provide to see if they could provide you with location update before relying back on last known position