How do I find the lat/long that is x km north of a given lat/long?

Question

I have some C# code that generates google maps. This codes looks at all the Points I need to plot on the map and then works out the Bounds of a rectangle to include those po

Answer 1

For lazy people, (like me ;) ) a copy-paste solution, Erich Mirabal's version with very minor changes:

using System.Device.Location; // add reference to System.Device.dll
public static class GeoUtils
{
    /// 

    /// Calculates the end-point from a given source at a given range (meters) and bearing (degrees).
    /// This methods uses simple geometry equations to calculate the end-point.
    /// 
    /// Point of origin
    /// Range in meters
    /// Bearing in degrees
    /// End-point from the source given the desired range and bearing.
    public static GeoCoordinate CalculateDerivedPosition(this GeoCoordinate source, double range, double bearing)
    {
        var latA = source.Latitude * DegreesToRadians;
        var lonA = source.Longitude * DegreesToRadians;
        var angularDistance = range / EarthRadius;
        var trueCourse = bearing * DegreesToRadians;

        var lat = Math.Asin(
            Math.Sin(latA) * Math.Cos(angularDistance) +
            Math.Cos(latA) * Math.Sin(angularDistance) * Math.Cos(trueCourse));

        var dlon = Math.Atan2(
            Math.Sin(trueCourse) * Math.Sin(angularDistance) * Math.Cos(latA),
            Math.Cos(angularDistance) - Math.Sin(latA) * Math.Sin(lat));

        var lon = ((lonA + dlon + Math.PI) % (Math.PI*2)) - Math.PI;

        return new GeoCoordinate(
            lat * RadiansToDegrees,
            lon * RadiansToDegrees,
            source.Altitude);
    }

    private const double DegreesToRadians = Math.PI/180.0;
    private const double RadiansToDegrees = 180.0/ Math.PI;
    private const double EarthRadius = 6378137.0;
}

Usage:

[TestClass]
public class CalculateDerivedPositionUnitTest
{
    [TestMethod]
    public void OneDegreeSquareAtEquator()
    {
        var center = new GeoCoordinate(0, 0);
        var radius = 111320;
        var southBound = center.CalculateDerivedPosition(radius, -180);
        var westBound = center.CalculateDerivedPosition(radius, -90);
        var eastBound = center.CalculateDerivedPosition(radius, 90);
        var northBound = center.CalculateDerivedPosition(radius, 0);

        Console.Write($"leftBottom: {southBound.Latitude} , {westBound.Longitude} rightTop: {northBound.Latitude} , {eastBound.Longitude}");
    }
}