Reverse Location.distanceBetween()

Question

I have a location with latitude and longitude and want to get a new location that has a distance of x meters from that location at an angle of d degrees. This would be the reverse of Location.distanceBetween(). Is there any Android API to do that. I know that I could program such a function myself, but I wonder if there is an API for it already.

Answer 1

It doesn't look like it.

Answer 2

Implement this yourself for now, but do expect this function to show up at some point, so code accordingly - create your own function, add a few unit tests.

In the future add the following to you function:

def myFunc(args):
  res = # compute stuff
  #if(debug):
    res2 = # make api call
    assert(res = res2)
  return res

And some time later:

def myFunc(args):
  return # make api call

And some time later remove the function altogether.

Answer 3

This is called the "first geodesic" (or sometimes "principal geodesic") problem, which will probably help you in finding an algorithm on Google if you need to implement this yourself.

Answer 4

There are some formulae and sample code (JavaScript) for this here: Movable Type Scripts. Look for 'Destination point given distance and bearing from start point'.

Here's an excerpt of the JavaScript from the site:

var lat2 = Math.asin( Math.sin(lat1)*Math.cos(d/R) + 
                      Math.cos(lat1)*Math.sin(d/R)*Math.cos(brng) );
var lon2 = lon1 + Math.atan2(Math.sin(brng)*Math.sin(d/R)*Math.cos(lat1), 
                             Math.cos(d/R)-Math.sin(lat1)*Math.sin(lat2));

In the above code, d is the distance, brng is the bearing in degrees, and R is the Earth's radius.

Porting this to Java should be trivial.