How to round double values returned by Interface Location

Question

How to round double values returned by Interface Location

Asked 7 years, 8 months ago

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1

I own a ArrayList that stores GPS coordinate objects and their elements are always being compared with the double values returned by the methods getLatitude() and getLongitude() of Interface Location.

Problem

From the tests I’ve done I found it very difficult that the Smartphone user capture a GPS coordinate exactly like any of the elements of my ArrayList. So the solution I find for this problem, is to round up the values double of the objects of my ArrayList and also round the double values returned by the methods getLatitude() and getLongitude() of Interface Location, to be able to detect more successfully when the user is near the places I intend to control.

Can anyone tell me how best to round up the doubles returned by the methods getLatitude() and getLongitude() or indicate another solution to this problem?

Down below follows my ArrayList:

ArrayList<Coordenada> coordenadasPKs = new ArrayList<>();
    coordenadasPKs.add(new Coordenada(41.148185, -8.584755, 336.1));
    coordenadasPKs.add(new Coordenada(40.82614, -8.59654, 296));
    coordenadasPKs.add(new Coordenada(40.168235, -8.62813666666667, 199));
    coordenadasPKs.add(new Coordenada(39.69546, -8.50684666666667, 135));
    coordenadasPKs.add(new Coordenada(39.6148033333333, -8.49502833333333, 125));
    coordenadasPKs.add(new Coordenada(39.411415, -8.52799166666667, 99));
    coordenadasPKs.add(new Coordenada(39.1335366666667, -8.761665, 59));

Already tested how it keeps using Math.round() of life?

– user42676

2016/10/16 at 17:00
i had to do this once with php to generate a more "precise" google map in case I didn’t arredondei , I only limited the houses because the latitudo is compasta for seconds degrees in case I limited to minutes

– Jasar Orion

2016/10/16 at 17:00
calculates all distances by Italics and picks up the object that generated the smallest of them

– guijob

2016/10/16 at 17:09
@Gamen, the problem I find in the Math Class round() method, is that it makes a rounding to a very short and inaccurate value.

– Vitor Mendanha

2016/10/16 at 17:25
@J. William, could you give me an example of how to do this?

– Vitor Mendanha

2016/10/16 at 17:25
@Vitormendanha Cara, I don’t know if it’s the best way to do this, I actually think it’s the worst possible, but have you ever thought about doing a cast of the value in a String, format it to two decimal places, sla, as many as you like, and then convert to double again?

– user42676

2016/10/16 at 21:07
@Gamen, I have tried unsuccessfully to use the Class: Decimalformat numberFormat = new Decimalformat("#.000"), to round the Latitude and Longitude values of the Location object and the Arraylist objects. I hoped to find other solutions that were more precise...

– Vitor Mendanha

2016/10/16 at 21:14
2

Here is a Haversine Java implementation, which calculates distance between 2 coordinates: http://stackoverflow.com/questions/23776344/haversine-formula-in-java-producing-incorrectresult - you can use this to evaluate the user’s closest points.

– Bacco

2016/10/16 at 22:25

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2 answers

2

Rounding up values may not be the best option.

What is normally used in this situation is the API Geofencingclient. It allows circular zones to be defined from a location and radius.

These zones are then monitored, and events are launched when the user enters or leaves this circle.

Giving a full explanation of how to use the API is something that would be too long for an answer.
You can find a tutorial here or consult Creating and Monitoring Geofences in the documentation.

Another option is to create Latlngbounds and check if the user’s location is inside it.

A Latlngbounds is a rectangle defined by the coordinates of its northeast and southwest corners.

You can create one from a coordinate and distance to the corners as follows:

//Calcula o ponto à distância 'raio' do 'centro*' na direção 45º(canto superior direito)
LatLng norhtEast = SphericalUtil.computeOffset(centro, raio, 45);

//Calcula o ponto à distância 'raio' do 'centro' na direção 225º(canto inferior esquerdo)
LatLng southWest = SphericalUtil.computeOffset(centro, raio, 225);

LatLngBounds bounds = new LatLngBounds(southWest,norhtEast);

Where

center - Latlng from the centre of the rectangle.
radius - Distance, in meters, from the center to the upper right(northeast) and lower left(southwest) corners of the Bounds

To check whether a Latlng is inside the Latlngbounds use:

boolean contains = bounds.contains(point);

Edit, after your comment.

If you are not using the google maps api you do not have access to the class Latlngbounds.

Basically what you want is to know whether or not the user is near a particular location. To determine this you only need to define what "being close" is and a way to calculate the distance between two coordinates.

To calculate the distance should be used spherical trigonometry, usually we use the "haversine formula".

As Bacco said, there are several implementations on the net, the class Sphericalutil of lib com.google.maps.android:android-maps-utils and this mine class helper, are examples of this.

Add a method to your class Coordinated indicating, according to the criterion(x meters), if the coordinates passed as argument are close to the.

private boolean isNear(int criterio, double lat, double long){

    return GeoMath.getDistance(this.lat, this.long, lat, long) <= criterio;
}

ramaral, my app does not use Google Maps, as it does not need it for the role it is performing. Question: if I add in Gradle the line "Compile 'com.google.android.gms:play-services-maps:9.6.1'", so that through an Interface Location object I can create Latlng Class objects, I could create Latlngbounds objects ?

– Vitor Mendanha

2016/10/16 at 20:09
Yes, I think that would be enough, but I find it a little exaggerated if the intention is just to use the Latlngbounds class. A less "heavy" solution is to use the com.google.maps.android:android-maps-utils:0.4+ to calculate the distance between coordinates. See this reply.

– ramaral

2016/10/16 at 21:56
Today I’m short on time, tomorrow I’ll complete the answer with an alternative to Bounds.

– ramaral

2016/10/16 at 22:00
2

If it is to calculate distance in two pairs of strings (the user and the point of interest), Haversine is simple and fast. It has online mount implementations. Probably the libs mentioned in the reply use something like this internally.

– Bacco

2016/10/16 at 22:17
@Bacco Yes it is true. A Sphericalutil that I refer uses Haversine. I myself have the mine "helper class".

– ramaral

2016/10/17 at 08:50
@ramaral, I created in my project a Geomath Class like yours, but I’m not getting to import the Geopoint Class? I added in Gradle the line Compile 'com.google.maps.android:android-maps-utils:0.4+' and I still don’t see the option to import the Geopoint Class?

– Vitor Mendanha

2016/10/17 at 11:05
Eliminate the method public static double getDistance(GeoPoint point1, GeoPoint point2) of my class and use the public static double getDistance(double startLatitude, double startLongitude,
 double endLatitude, double endLongitude)

– ramaral

2016/10/17 at 11:10
There is another problem: It is not possible to add in Gradle the line 'com.google.maps.android:android-maps-utils:0.4+', because Android Studio shows errors in the file: C: Users Menda Androidstudioprojects Testes_gps_2 app build Intermediates manifests full debug Androidmanifest.xml

– Vitor Mendanha

2016/10/17 at 11:12
If you want to use my class you don’t need com.google.maps.android:android-maps-utils:0.4+

– ramaral

2016/10/17 at 11:14
right, but your "class helper" class has Geopoint class objects that can’t care?

– Vitor Mendanha

2016/10/17 at 11:19
Also eliminate the getGeoPointAlongBearing. It is not necessary for distance calculation. Geopoint is a class of the old google maps api.

– ramaral

2016/10/17 at 11:22
the "isNear" method, which he exemplified above, does not seem to be well discriminated ? Se eu criar um assim está correto: private boolean isNear(int criterio, double startLatitude, double startLongitude, double endLatitude, double endLongitude){

 return GeoMath.getDistance(startLatitude, startLongitude, endLatitude, endLongitude) <= criterio;
 }

– Vitor Mendanha

2016/10/17 at 11:26
If the method is created in its Coordinates class, it already has the startLatitude, startLongitude, no need to pass them. That’s what I meant by this.lat, this.long

– ramaral

2016/10/17 at 11:28
1

@ramaral, you are right in what I need to solve my problem, that is, the best solution will be to check if the user is close to any of the coordinates of the Arraylist coordinates. I will take your reply as accepted. Thank you.

– Vitor Mendanha

2016/10/17 at 15:45

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by guijob • **1,809** points · Answer 1 · 2016-10-16T17:51:54+00:00

As I suggested in the commentary:

int indice = 0;

// lat - latitude do cliente
// lon - longitude do cliente

double menorDistanciaAoQuadrado = Math.Pow(coordenadasPKs[i].getLatitude() - lat, 2) + Math.Pow(coordenadasPKs[i].getLongitude() - lon, 2);

double distanciaAoQuadrado;
for (int i = 1; i < coordenadasPKs.length; i++) {
    distanciaAoQuadrado = Math.Pow(coordenadasPKs[i].getLatitude() - lat, 2) + Math.Pow(coordenadasPKs[i].getLongitude() - lon, 2);
    if (distanciaAoQuadrado < menorDistanciaAoQuadrado) {
        menorDistanciaAoQuadrado = distanciaAoQuadrado;
        indice = i;
    }
}

The nearest point is coordenadasPKs[indice]. So I would solve this problem.