Develop Reference

Plotting coordinates on Route in Gmap (Google Maps Android API)

I'm currently working on one Android application using Google map.
My requirement is to draw a route between source-destination and plot markers at every 500 meters on that route.
I have drawn a route, but not getting how to plot markers at every 500 meters. Is there any Google API available to get coordinates on route, or I have to implement any other logic?

Objectives
The objective is getting a list of LatLng coordinates along the route returned by the Directions API web service at every N meters. Later we can create markers for this list of coordinates.
Solution
The solution has two steps. The first one is getting a list of LatLng that form a route returned by Directions API. You can use a Java Client for Google Maps Services to execute Directions API request and extract a list of LatLng. Have a look at private List<LatLng> getDirectionsPathFromWebService(String origin, String destination) method in my example. This method calls Directions API and loop through legs and steps of the route object to get a complete list of LatLng that form a route.
The second step is implemented in the method private List<LatLng> getMarkersEveryNMeters(List<LatLng> path, double distance). It loops through all LatLng from the first step and creates a list of LatLng at every N meters where N is a distance in meters passed as a second parameter of the method. This method uses internally SphericalUtil class from the Google Maps Android API Utility Library. Have a look at comment to figure out what is happening in this method.
Finally, I create markers from the list that was obtained in second step.
Code snippet
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {
private GoogleMap mMap;
private String TAG = "so47784512";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
#Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
String origin = "Avinguda Diagonal, 101, 08005 Barcelona, Spain";
String destination = "Carrer de París, 67, 08029 Barcelona, Spain";
LatLng center = new LatLng(41.391942,2.179413);
//Define list to get all latlng for the route
List<LatLng> path = this.getDirectionsPathFromWebService(origin, destination);
//Draw the polyline
if (path.size() > 0) {
PolylineOptions opts = new PolylineOptions().addAll(path).color(Color.BLUE).width(5);
mMap.addPolyline(opts);
}
List<LatLng> markers = this.getMarkersEveryNMeters(path, 500.0);
if (markers.size() > 0) {
for (LatLng m : markers) {
MarkerOptions mopts = new MarkerOptions().position(m);
mMap.addMarker(mopts);
}
}
mMap.getUiSettings().setZoomControlsEnabled(true);
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(center, 13));
}
private List<LatLng> getDirectionsPathFromWebService(String origin, String destination) {
List<LatLng> path = new ArrayList();
//Execute Directions API request
GeoApiContext context = new GeoApiContext.Builder()
.apiKey("AIzaSyBrPt88vvoPDDn_imh-RzCXl5Ha2F2LYig")
.build();
DirectionsApiRequest req = DirectionsApi.getDirections(context, origin, destination);
try {
DirectionsResult res = req.await();
//Loop through legs and steps to get encoded polylines of each step
if (res.routes != null && res.routes.length > 0) {
DirectionsRoute route = res.routes[0];
if (route.legs !=null) {
for(int i=0; i<route.legs.length; i++) {
DirectionsLeg leg = route.legs[i];
if (leg.steps != null) {
for (int j=0; j<leg.steps.length;j++){
DirectionsStep step = leg.steps[j];
if (step.steps != null && step.steps.length >0) {
for (int k=0; k<step.steps.length;k++){
DirectionsStep step1 = step.steps[k];
EncodedPolyline points1 = step1.polyline;
if (points1 != null) {
//Decode polyline and add points to list of route coordinates
List<com.google.maps.model.LatLng> coords1 = points1.decodePath();
for (com.google.maps.model.LatLng coord1 : coords1) {
path.add(new LatLng(coord1.lat, coord1.lng));
}
}
}
} else {
EncodedPolyline points = step.polyline;
if (points != null) {
//Decode polyline and add points to list of route coordinates
List<com.google.maps.model.LatLng> coords = points.decodePath();
for (com.google.maps.model.LatLng coord : coords) {
path.add(new LatLng(coord.lat, coord.lng));
}
}
}
}
}
}
}
}
} catch(Exception ex) {
Log.e(TAG, ex.getLocalizedMessage());
}
return path;
}
private List<LatLng> getMarkersEveryNMeters(List<LatLng> path, double distance) {
List<LatLng> res = new ArrayList();
LatLng p0 = path.get(0);
res.add(p0);
if (path.size() > 2) {
//Initialize temp variables for sum distance between points and
//and save the previous point
double tmp = 0;
LatLng prev = p0;
for (LatLng p : path) {
//Sum the distance
tmp += SphericalUtil.computeDistanceBetween(prev, p);
if (tmp < distance) {
//If it is less than certain value continue sum
prev = p;
continue;
} else {
//If distance is greater than certain value lets calculate
//how many meters over desired value we have and find position of point
//that will be at exact distance value
double diff = tmp - distance;
double heading = SphericalUtil.computeHeading(prev, p);
LatLng pp = SphericalUtil.computeOffsetOrigin(p, diff, heading);
//Reset sum set calculated origin as last point and add it to list
tmp = 0;
prev = pp;
res.add(pp);
continue;
}
}
//Add the last point of route
LatLng plast = path.get(path.size()-1);
res.add(plast);
}
return res;
}
}
Conclusion
You can see a result of sample code in the following screenshot
The sample project can be found on GitHub:
https://github.com/xomena-so/so47784512
Do not forget to replace an API key with your's.
I hope this helps!

Chat Application with Maps

I want to build a basic chat application which includes location sharing. I proficient enough in Java, but haven't worked enough on Android Platform. How do I approach this problem and what are the steps to be taken?

Send location values latitude and longitude to the other person via chat message. You can get user's last known location by:
private double[] getGPS()
{
LocationManager lm = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
List<String> providers = lm.getProviders(true);
/* Loop over the array backwards, and if you get an accurate location, then break out the loop */
Location l = null;
for (int i = providers.size() - 1; i >= 0; 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;
}

Polylines appearing on map where they shouldn't

I have a array of about 7000 locations, each one was recorded using the location manager on android, when loading these locations I filter out any that are further then 1km from the previous or have an accuracy higher then 50 using this:
if (c.moveToFirst())
do {
lat = c.getString(0);
lng = c.getString(1);
ac = c.getString(2);
alt = c.getString(3);
if (l1 != null) {
l2 = new Location("MAP");
l2.setLatitude(Double.parseDouble(lat));
l2.setLongitude(Double.parseDouble(lng));
l2.setAltitude(Double.parseDouble(alt));
l2.setAccuracy(Float.parseFloat(ac));
if (l1.distanceTo(l2) < 1000
&& l2.getAccuracy() < 51) {
opts.add(new LatLng(Double.parseDouble(lat),
Double.parseDouble(lng)));
list.add(l2);
l1 = l2;
}
} else {
l1 = new Location("MAP");
l1.setLatitude(Double.parseDouble(lat));
l1.setLongitude(Double.parseDouble(lng));
l1.setAccuracy(Float.parseFloat(ac));
l1.setAltitude(Double.parseDouble(alt));
if (l1.getAccuracy() > 50)
l1 = null;
}
} while (c.moveToNext());
So that removes the possibilities for these random lines assuming its working as it should.
When it is working correctly it should come up like this:
However, when I zoom in a little more or move around sometimes I get these random lines:
Im adding the lines like this:
Location[] locations = Arrays.copyOfRange(mLocations, a, b);
if (mStartLine != null)
mStartLine.remove();
if (mMiddleLine != null)
mMiddleLine.remove();
if (mEndLine != null)
mEndLine.remove();
if (mMarker != null) {
mMarker.remove();
mMarker = null;
}
PolylineOptions so = new PolylineOptions();
PolylineOptions mo = new PolylineOptions();
PolylineOptions eo = new PolylineOptions();
so.color(Color.GREEN);
eo.color(Color.GREEN);
mo.color(Color.BLACK);
if (locations.length < 2) {
if (locations.length == 0)
return;
// Add just a dot instead.
MarkerOptions m = new MarkerOptions();
m.position(new LatLng(locations[0].getLatitude(), locations[0]
.getLongitude()));
mMarker = mMap.addMarker(m);
return;
}
so.add(new LatLng(locations[0].getLatitude(), locations[0].getLongitude()));
so.add(new LatLng(locations[1].getLatitude(), locations[1].getLongitude()));
mStartLine = mMap.addPolyline(so);
for(int i = 1; i < (locations.length - 1); i++){
mo.add(new LatLng(locations[i].getLatitude(), locations[i].getLongitude()));
}
mMiddleLine = mMap.addPolyline(mo);
eo.add(new LatLng(locations[locations.length - 2].getLatitude(), locations[locations.length - 2].getLongitude()));
eo.add(new LatLng(locations[locations.length - 1].getLatitude(), locations[locations.length - 1].getLongitude()));
mEndLine = mMap.addPolyline(eo);
The bar at the bottom is a selector to only show that span of locations (Because when you have something like 7000 locations showing then it gets pretty crazy and you get StackOverflowError's)

There appears to be a bug open for it: https://code.google.com/p/gmaps-api-issues/issues/detail?id=5313
EDIT
It appears if you filter vertices that are closer than 1 meter to each other the the bug is resolved. I will write some code to fix this later tonight and put it here.
UPDATE
This bug was handled in Google issue tracker
https://issuetracker.google.com/issues/35821816
It was fixed in Google Play Services - 9.2.56
https://developers.google.com/maps/documentation/android-api/releases#june_27_2016

Here is an approach that fixed this issue for us. Not necessarily the ideal solution, but it works. At certain zoom levels you may see a polyline extend beyond where it should be (like the pictures show above). If you keep changing your zoom level the extension would disappear and then reappear. This happened to us everytime when two coordinates were exactly the same. e.g.
Lets say you have 3 coordinates A,B,C. Bus starts from A and goes to B, the bus then turns around and comes to C. If A and C are the exact same coordinates you would see this polyline extension problem.
After a few approaches we settled on offseting the latitude of point C by .00001. That has fixed all our issues.

NullPointerException Sometimes

I have a function in my application and when user clicks button, it will display the nearest office. Functionality works in part of Sweden but does not work in the north of Sweden. I use try-catch statement and I'll catch the null pointer exception. When I shut down my network and the location, I get the error message, but in north Sweden, there is no message, the app just crashes. My code is down there. onFindOfficeClick () is a single function and independent. How can I solve this problem? I tried debug but fails to hit the error ... do not know what to do. I take all coordinates from xml file. Does anybaody have any suggestions?
private void onFindOfficeClick() {
try {
LocationManager lm = (LocationManager)getSystemService(Service.LOCATION_SERVICE);
List<String> providersName = lm.getProviders(false);
if(providersName.size()>0){
Location location = lm.getLastKnownLocation(providersName.get(0));
float results [] = new float [1];
final double longitude = location.getLongitude();
final double latitude = location.getLatitude();
final int officeCount = mOfficesInfo.length;
double minDistance = 0;
int officeNum = 0;
for(int i=0; i<officeCount; i++){
Location.distanceBetween(latitude, longitude,
mOfficesInfo[i].getLatitude(), mOfficesInfo[i].getLongitude(), results);
if(i==0){
minDistance = results[0];
} else if(results[0]<minDistance){
minDistance=results[0];
officeNum = i;
}
}
int countryPosition = mCountries.indexOf(mOfficesInfo[officeNum].getCountry());
mCountrySpiner.setSelection(countryPosition);
mFindedOfficeName = mOfficesInfo[officeNum].getOfficeName();
mOfficesSpiner.setSelection(officeNum);
}
}
catch (NullPointerException e)
{
Toast.makeText(getApplicationContext(),"check your network and GP:s connections",Toast.LENGTH_SHORT).show();
}
}

put a null check before calling
LocationManager lm = (LocationManager)getSystemService(Service.LOCATION_SERVICE);
if(lm!=null){
lm.getProviders(false);.
}
and also might be
Location location = lm.getLastKnownLocation(providersName.get(0));
giving you null in the location variable so just do modify your code and put null check before getting latitude and laongitude from location.
if(location!=null){
final double longitude = location.getLongitude();
final double latitude = location.getLatitude();
}
becuase it is not good practice to catch NullPointerException in you code.

GPS - Getting the distance,time while running and walking

i have a situation where i need to use GPS technique.
i need to find the distance between two points when the person is walking.
When the person starts walking he will click on Start button and when he stops he clicks on stop button
after this it should show him
1.time taken
2.Distance travelled in Kms.
3.from where to where(places name) eg: a to b
Do i need to have google maps for this?
I saw the code here link to get the current location which gives me latitude longitude.
please help how to go with this
**
Edited:
**
This is the code i am using
private EditText editTextShowLocation;
private Button buttonGetLocation;
private ProgressBar progress;
private LocationManager locManager;
private LocationListener locListener = new MyLocationListener();
private boolean gps_enabled = false;
private boolean network_enabled = false;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
editTextShowLocation = (EditText) findViewById(R.id.editTextShowLocation);
progress = (ProgressBar) findViewById(R.id.progressBar1);
progress.setVisibility(View.GONE);
buttonGetLocation = (Button) findViewById(R.id.buttonGetLocation);
buttonGetLocation.setOnClickListener(this);
locManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
}
#Override
public void onClick(View v) {
progress.setVisibility(View.VISIBLE);
// exceptions will be thrown if provider is not permitted.
try {
gps_enabled = locManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
} catch (Exception ex) {
}
try {
network_enabled = locManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
} catch (Exception ex) {
}
// don't start listeners if no provider is enabled
if (!gps_enabled && !network_enabled) {
AlertDialog.Builder builder = new Builder(this);
builder.setTitle("Attention!");
builder.setMessage("Sorry, location is not determined. Please enable location providers");
builder.setPositiveButton("OK", this);
builder.setNeutralButton("Cancel", this);
builder.create().show();
progress.setVisibility(View.GONE);
}
if (gps_enabled) {
locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locListener);
}
if (network_enabled) {
locManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locListener);
}
}
class MyLocationListener implements LocationListener {
#Override
public void onLocationChanged(Location location) {
if (location != null) {
// This needs to stop getting the location data and save the battery power.
locManager.removeUpdates(locListener);
String londitude = "Londitude: " + location.getLongitude();
String latitude = "Latitude: " + location.getLatitude();
String altitiude = "Altitiude: " + location.getAltitude();
String accuracy = "Accuracy: " + location.getAccuracy();
String time = "Time: " + location.getTime();
editTextShowLocation.setText(londitude + "\n" + latitude + "\n" + altitiude + "\n" + accuracy + "\n" + time);
progress.setVisibility(View.GONE);
}
}
#Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
#Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
#Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
}
#Override
public void onClick(DialogInterface dialog, int which) {
if(which == DialogInterface.BUTTON_NEUTRAL){
editTextShowLocation.setText("Sorry, location is not determined. To fix this please enable location providers");
}else if (which == DialogInterface.BUTTON_POSITIVE) {
startActivity(new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS));
}
}
It is showing the Logitude Latitude which i am entering from emulator control.
In this i am manually entering the details of longitude and latitude
by going to window->showview->other->emulator control for testing in the emulator
but what i need is i will have two edittext where i enter the place name(A) and (B)
it should give me the distance
please help

try using Google Distance Matrix Api
https://developers.google.com/maps/documentation/distancematrix/

You can use currentTimeinMillis() to get your start and end time for your journey.
You can then use the formulas explained here to find the distance and lastly you will have to use a reverse geocoding service such as Nominatim to be able to get the address of a place from your GPS coordinates.
That being said, the distance formula will get you the distance between one point and the next, not the actual displacement. If this is not what you need, but rather you want the actual distance travelled you will need to calculate this value at a shorter interval.

You can find out the distance between two locations(in terms of latitude and longitude) by making use of Spherical Trigonometry
Coming to time make use of simple date objects and compare the startTime and endTime.
(OR)
You can get approximate distance using below code
double distance;
Location locationA = new Location("point A");
locationA.setLatitude(latA);
locationA.setLongitude(lngA);
Location locationB = new Location("point B");
locationB.setLatitude(latB);
LocationB.setLongitude(lngB);
distance = locationA.distanceTo(locationB);

For getting the distance between 2points(A to B) there is a function called distanceTo in android.
For e.g.
double distance = startLocation.distanceTo(finishLocation)/1000;
For time taken as npinti said you can use currentTimeinMillis() or you can also use Timer and show it to user when he clicks on start button. Its just like stopwatch.
Edited
Place A - New York
Place B - Paris
In this case you first need to convert the string into Location(i.e you need latitude & longitude). For that you have use the concept of Geocoding.
List<Address> foundGeocode = null;
foundGeocode = new Geocoder(this).getFromLocationName("address here", 1);
foundGeocode.get(0).getLatitude(); //getting latitude
foundGeocode.get(0).getLongitude();//getting longitude
After that you can calculate the distance from the distanceTo method.
Hope this will help....

I suppose the question is one of walking..
Are you walking on the streets, or as the crow flies?
If it's streets, and your connected to the net, use google's api.. It calculates routing based on two points and returns XML.. Should be easy enough to figure out.
If it's crow flies.. well then, just do (a*a) + (b*b) = (c*c) this is by far the easier..
You could have your user tap for major turns.. Or you could keep a runnable running every 10 seconds from when they hit start, and plot the points. Still a*a+b*b=c*c but just a bunch of steps.
Of course you'd have to run it in a service.. And given the choice I'd go with that option. You could adjust the cycle time based on speed traveled. Faster would be smaller pauses.
It requires less on your dataplan.
EDIT
Ah.. I see what you're looking for. Tis not what I thought you were asking for.
Simplify.. convert lat/long to GPS. and then do simple math on the last point stored
void addDistance()
{
newX = ...
newY = ...
deltaX = absolute(m_oldX - newX)
deltaY = absolute(m_oldY = newY)
m_distance += sqrt(deltaX^2 + deltaY^2);
m_oldX = newX;
m_oldY = newY;
}
void startOver()
{
newX = ...
newY = ...
m_distance = 0;
m_oldX = newX;
m_oldY = newY;
}