Develop Reference

Geo Coordinates (Long,Lat) to Meters (x,y)

I am working coordinates system as shown below:
x and y are in meters. I am interested in only positive x,y. I want to convert (x,y) to (lat,lon) and vise versa.
I thought it is simple and I dont see a problem with my solutions below. But I am not getting very correct results.
My Solution:
As we see in the image below, I considered the Latitude and Longitude as angles of 2 circles:
1. (x,y) to (lat,lon)
I applied the Arc Length formula (here), shown below, on both; x and y
Hence, my functions are:
private static double calculateLat(float x) {
int earthRadius = 6371000;
return REF_LOC.getLatitude() + x*360/(2*PI*earthRadius);
}
private static double calculateLong(float y) {
int earthRadius = 6371000;
return REF_LOC.getLongitude() + y*360/(2*PI*earthRadius);
}
REF_LOC is the reference Geo Location for which (x,y) are (0,0). It can be any point on earth.
2. (lat,lon) to (x,y)
For this I am simply using this:
int calculateX(double longitude){
Location.distanceBetween(REF_LOC.getLatitude(), REF_LOC.getLongitude(),
REF_LOC.getLatitude(), lonDeg, results);
return results[0];
}
int calculateY(double latitude){
Location.distanceBetween(REF_LOC.getLatitude(), REF_LOC.getLongitude(),
latDeg, REF_LOC.getLongitude(), results);
return results[0];
}
But I am getting inconsistent results. First I use solution 1 and convert some value (x,y) to (lat,long). But when I use the same (lat,long) back to (x,y) using solution 2, I get about 2 meters difference in x and 10 meters in y. Can anyone help me identify the problem please?

Alluding to my comment on spherical vs elliptical calculations, another way to look at difference in distance calculations for spherical vs elliptical distance is to use the 2 available utilities:
// For REF_LOC = (70, 20)
// Compute a lat/lng due east of a REF_LOC and compute distance using both
// available methods.
LatLng P = SphericalUtil.computeOffsetOrigin(REF_LOC, 20000, 90.0);
// And then compute a distance
d = SphericalUtil.computeDistanceBetween(REF_LOC, P);
Location.distanceBetween(REF_LOC.latitude, REF_LOC.longitude, P.latitude, P.longitude, results);
// d = 20000.000000000036
// results[0] = 20081.818
// and for a REF_LOC = (0, 20)
// d = 20000.000000000127
// results[0] = 20022.377
What's also interesting is the SphericalUtil.computeOffsetOrigin() produces error
in latitude increasing from equator to pole making it non-symmetrical. Yet the resulting distances are essentially exact.
I'd recommend using SphericalUtil.computeOffsetOrigin to compute the X/Y breaking
it into the latitude and longitude offsets as you are doing.
Finally demonstrating the SphericalUtil solution:
// Start with some arbitrary x/y relative to REF_LOC
double Rx = 125.0;
double Ry = 73.0;
// Compute a lat/lon from REF_LOC to the point
LatLng Rll = new LatLng(SphericalUtil.computeOffsetOrigin(REF_LOC, Ry, 180).latitude,
SphericalUtil.computeOffsetOrigin(REF_LOC, Rx, 270).longitude);
// And recompute the x/y components of the lat/lon
double Rxx = SphericalUtil.computeDistanceBetween(REF_LOC, new LatLng(REF_LOC.latitude, Rll.longitude));
double Ryy = SphericalUtil.computeDistanceBetween(REF_LOC, new LatLng(Rll.latitude, REF_LOC.longitude));
Resulting in:
Rx/Ry = (125.0, 73.0)
Rxx/Ryy = (125.00000004545973, 73.00000000137051)
Acceptable error I assume.
So the parting question is - what does the x/y really represent?
Reference the source for both utilities for more information:
Location
SphericalUtil

Measure the distance between two locations by road

How can I measure distance between two location by road in my Android application? I wrote code that measure the distance in a straight line, but I need code for shortest distance by road. What should I change in my code for it?
public double updateDistance(Location location) {
float results[] = new float[3];
Location.distanceBetween(location.getLatitude(),
location.getLongitude(), mLatitude, mLongitude, results);
distance = results[0];
return distance;
}

Use the google maps api instead
https://developers.google.com/maps/documentation/distance-matrix/intro?hl=en
you can see this too
Google Map API v2 - Get Driving Distance from Current Location to Known Locations

How to convert lat lng to a Location variable?

I am making a map app in android, I want to get 2 locations on the map, and see the distance between them. I already got my current location as a "Location" variable. The other place however is saved as two variables : double lat,lng;
I have checked the internet and found this method that will help :
float distance = myLocation.distanceTo(temp);
The problem is that the "temp" I have is not a "Location", it is 2 different doubles.
Is there a way to convert them to Location?
PS. Code i tried but did't work :
Location temp = null;
temp.setLatitude(23.5678);
temp.setLongitude(34.456);
float distance = location.distanceTo(temp);
Problem :
Null pointer access: The variable temp can only be null at this location

You have to instantiate Location, before accessing its members. For example
Java
Location temp = new Location(LocationManager.GPS_PROVIDER);
temp.setLatitude(23.5678);
temp.setLongitude(34.456);
float distance = location.distanceTo(temp);
Kotlin
val distance = location.distanceTo(Location(LocationManager.GPS_PROVIDER).apply {
latitude = 23.5678
longitude = 34.456
})

Alternatively, you can get the distance without instantiating a Location object at all using the static method Location.distanceBetween().
float[] results = new float[1];
Location.distanceBetween(1, 2, 2 , 2, results);
public static void distanceBetween (double startLatitude, double
startLongitude, double endLatitude, double endLongitude, float[]
results)
The computed distance is stored in results[0]. If results has length 2
or greater, the initial bearing is stored in results1. If results
has length 3 or greater, the final bearing is stored in results[2].
Parameters
startLatitude the starting latitude
startLongitude the starting longitude
endLatitude the ending latitude
endLongitude the ending longitude
results an array of floats to hold the results

Moving GPS coordinate

I am fairly new to Android programming, but I am getting pretty good at it (I think: ))
What I am doing is building a situated stories app. It is an app that places audio files at certain GPS markers and enables the user to listen to them at specific locations.
The next step is moving audio files. What I want to do is set a marker at a specific position in a city. (done). Next I want to check the location of a second marker that moves in a circle around it.
What I have so far is this:
public void checkCircularPosition(){
/*
* could be a solution?
*
radius = 250; //offset in meters
gpsLatCenter = 5.1164; //?how can i make this accurate in meters?
gpsLonCenter = 52.0963; //??how can i make this accurate in meters?
degree = 0; //should be variable over time (full circle in 1Hr, 3600sec --> 360/3600 = 0,1 deg/s)
radian;
radian = (degree/180)*Math.PI;
gpsCircleLat = gpsLatCenter+Math.cos(radian)*radius;
gpsCircleLon = gpsLonCenter-Math.sin(radian)*radius;
*/
}
Now, I have checked this code in adobe flash, which made a movie clip move around in a circle. So I know the calculations are somewhat right. But, I have no way of calculating the latitude and longitude of the resulting coordinates.
EDIT!!
i found the solution with the help posted below. still a lot of work to figure out how to use the results. anyway, i posted the resulting function below.
to make this work, you need _radius wich is 6371 (earth's radius), a bearing, a distance, and a start location.
thanks a lot guys!
public static void destinationPoint(double brng, double dist) {
dist = dist/_radius; // convert dist to angular distance in radians
brng = Math.toRadians(brng); //
double lat1 = Math.toRadians(_lat);
double lon1 = Math.toRadians(_lon);
double lat2 = Math.asin( Math.sin(lat1)*Math.cos(dist) + Math.cos(lat1)*Math.sin(dist)*Math.cos(brng) );
double lon2 = lon1 + Math.atan2(Math.sin(brng)*Math.sin(dist)*Math.cos(lat1), Math.cos(dist)-Math.sin(lat1)*Math.sin(lat2));
lon2 = (lon2+3*Math.PI) % (2*Math.PI) - Math.PI; // normalise to -180..+180º
Log.i(APPTAG, ""+Math.toDegrees(lat2));
Log.i(APPTAG, ""+Math.toDegrees(lon2));
Location movLoc = new Location("");
movLoc.setLatitude(Math.toDegrees(lat2));
movLoc.setLongitude(Math.toDegrees(lon2));
Log.i(APPTAG, ""+movLoc);
}

You should check the section Destination point given distance and bearing from start point at this website: http://www.movable-type.co.uk/scripts/latlong.html
That website has the proper formula for using your start point (gpsLatCenter/gpsLonCenter) and bearing (degree in you code) to compute the final lat/lon (gpsCircleLat/gpsCircleLon).

Issue in setting latitude and longitude in android

I am trying to pass latitude and longitude to another activity and check the distance between this passed co-ordinates and the current co-ordinate.
In the first activity:
GeoPoint p1 = mapView.getProjection().fromPixels((int) event.getX(),(int event.getY());
setter(p1.getLatitudeE6()/ 1E6, p1.getLongitudeE6() /1E6);
public void setter(Double lati,Double longi)
{
latitude=lati;
longitude=longi;
}
on the button click event i am passing this with the help of a bundle. This works fine.
In the second activity:
public Location selected_location=null;
Double lati,longi;
Bundle b=this.getIntent().getExtras();
lati=b.getDouble("latitude");
longi=b.getDouble("longitude");
Till this much it works fine. I even printed the values. The real issue is the the lines given below:
selected_location.setLatitude(lati);
selected_location.setLongitude(longi);
I am trying to set the passed latitude and longitude values to a location variable. But this is causing the activity to terminate.
If possible please suggest a solution. If the question is childish please ignore.

If you aim to calculate only the distance you do not need to construct Location objects use this method. It is static and works with long and lat values. I can also help debuging the error if you put the stack trace of the exception.
EDIT The requested example:
float myGetDistance(double startLatitude, double startLongitude, double endLatitude, double endLongitude) {
float [] results = new float[1]; // You need only the distance, thus only one element
Location.distanceBetween(startLatitude, startLongitude, endLatitude, endLongitude, results);
return results[0];
}

You can complete the distance between two points given by it coordinates like this:
final float[] results= new float[1];
// The computed distance in meters is stored in results[0].
// If results has length 2 or greater, the initial bearing is stored in results[1].
// If results has length 3 or greater, the final bearing is stored in results[2].
Location.distanceBetween(refLat, refLong, latitude, longitude, results);
final float distance = results[0]; // meter!
You may reuse the results array for later computations. If you need bearing information use declare the result array of size 3, if you do not need it use size 1 and save the time for the computation of the not needed information this way.