DistanceTo() with string

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Hi folks,

I'm newish to android, very inexperienced. I'm trying to develop an application that transmits the coordinates of one phone (client a) to (client b) via a java server, I then want to check the distance between clients. I have managed to get the coordinates of client a, send them via a socket to the server and then onto client b. The problem is I send them in a string format. In order to make use to make use of the distanceTo() method in the android.loaction I need to have a double lat and double long of client a.

I'm just attaching a snippet of code from client a how I'm sending the coordinates.

Java

public void onLocationChanged(Location location) {
            // TODO Auto-generated method stub
             latitude = location.getLatitude();
             longitude = location.getLongitude();
             coordinates = (""+latitude + longitude);
             Transmit(coordinates);         
        }

The transmit method is a follows

Java

private void Transmit(final String message) {
    Thread trans = new Thread(new Runnable() {
        public void run() {
            Log.d("TRANSMIT", "CALLED");
            // TODO Auto-generated method stub
            try {
                s = new Socket("192.168.1.1", 2222); // connect to
                                                        // server
                Log.d("CONNECTED", "Connected");
                DataOutputStream _OutPut = new DataOutputStream(
                        s.getOutputStream());
                _OutPut.writeBytes(message + "\n");
                _OutPut.flush();
                _OutPut.close();
            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    });
    trans.start();

So client b recieves the coordinates as a string and I'm unsure as to how to use the coorinates in string format in the distanceTo() method or how to extract them out of a string, or should i send them in a double array? So I need to take them out as individual doubles i.e.

Java

client a lat = client a long =

Any help on this would be appreciated, as I'm starting to find my feet but there are certain things that throw up problems.

Thanks in advance.

Regards,
Gary

Posted 17-Mar-13 6:48am

GaryDoo

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Prasad Khandekar · Accepted Answer · 2013-03-17T07:52:00

Solution 1

Hello,
First of all I will suggest to use a separator or a JSON structure to transmit this information. This way on client you do not have any problems separating the latitude & Longitude values. Now converting a string to numeric form can easily be achieved using

Java

double lat = DOuble.parseDouble("latitude_value_string")

I am putting a pseudo code below.

JavaScript

public void onLocationChanged(Location location) {
    // TODO Auto-generated method stub
    latitude = location.getLatitude();
    longitude = location.getLongitude();
    coordinates = ("" + latitude + "," + longitude);
    Transmit(coordinates);         
}

On the receiving your code will look like something below, assuming that you have retrieved the string in strData.

C#

string[] coOrds = strData.split(ne Char[] {','});
double latitude = Double.parseDouble(coOrds[0]);
double longitude = Double.parseDouble(coOrds[1]);
}

Regards,

Posted 17-Mar-13 7:52am

Prasad Khandekar

Updated 17-Mar-13 19:53pm

v2

Comments

GaryDoo 17-Mar-13 15:26pm

Hi Prasad, thank you for your speedy reply, I had looked at parseDouble already, however, this issue I was having was that there are two doubles within the one string a latitude double and a longitude double. I'm wondering how, when I have the following line of code

double lat = double.parseDouble(location);

do I extract or parse one of the doubles? i.e. the latitude double?

I have used tcp/ip sockets to transmit the coordinates, now as I've said I'm quite inexperienced in android/java, could you explain the JSON structure method or separator method?

Regards,
Gary

Prasad Khandekar 18-Mar-13 1:53am

Hello,

I have updated the solution with example.

Regards,

GaryDoo 3-Apr-13 13:50pm

Prasad...I've tried to implement this, but I seem to get errors...

String[] Loc = location.split(",");
double Clatitude = Double.parseDouble(Loc[0]);
double Clongitude = Double.parseDouble(Loc[1]);

These are the lines of code I am using to split the string and then to parse them to doubles, does this look incorrect to you?

Prasad Khandekar 3-Apr-13 16:19pm

In order for this to work you need to ensure that the location string indeed contains the coordinates separated by the comma ",". Also you can add a condition (loc.length > 1) then compute Clongitude.

What is the error you are getting?

GaryDoo 3-Apr-13 17:06pm

my apologies Prasad, it was an oversight on my behalf, I was testing with a simple string and had forgotten to comment it out, it was this that was causing me errors as it was trying to split a string with no ","!!!

However, if I could I would like to ask your advice, is there anyway for me to test that these 'Clatitude' and 'Clongitude' are correct? Is there any way to display them for testing purpose? I am trying to calculate the distance and display it, I am using the following code
(should I open a new discussion?)

public void onLocationChanged(Location location) {
// TODO Auto-generated method stub
Location parent = new Location("parent");

Platitude = location.getLatitude();
Plongitude = location.getLongitude();

parent.setLatitude(Platitude / 1e6);
parent.setLongitude(Plongitude / 1e6);

Location child = new Location("child");

child.setLatitude(Clatitude / 1e6);
child.setLongitude(Clongitude / 1e6);

distance = parent.distanceTo(child);

String distanceSt = String.valueOf(distance);

TextView myTextview = (TextView) findViewById(R.id.distTo);
myTextview.setText(distanceSt);
}
}
I am testing with a mobile device and an emulator. I sent test coordinates to the emulator an I got a result of 9.5 meters, so to test I input the coordinates of my mobile device and I get a distance of 9.3 meters where I'm sure this should be zero.

Can you see where I'm going wrong?

Regards,
Gary

Prasad Khandekar 3-Apr-13 17:40pm

Since you are using LocationManeger Listener the readings you are getting are almost correct. Please have a look at this document in Android SDK to get more info on how to accurately get the user's location. Will also suggest to have a look at this (http://code.google.com/p/andtracker/source/browse/trunk/LiveTracker/src/de/avanux/android/livetracker2/LocationTracker.java) sample to know more on accurately passing the location to a remote entity.

GaryDoo 3-Apr-13 18:07pm

if I pass coordinates from a point at the other end of the country I still get a reading of 9. something. This surely can't be right?

Prasad Khandekar 4-Apr-13 3:58am

Hello,

Please have a look at the sample link, it shows the correct way of passing Locatioon object over wire reconstruct it at other end and compute the distance. Android Location object it self has got the method to compute the distance.