Question

I have been able to draw an ellipse on my map using latitude and longitude values around a given center point. Although I see a shape on the map, I get an ellipse instead of a circle and I don’t think it matches the distance specified. I intend to use this to display objects within that circle (this will be done later on once I can get the circle displaying properly, which is the reason why i need a circle not an ellipse as it should be perfectly round).

I am using a Bing Maps API. I wish to draw the circle in a given miles (distance) from the center which has been passed in through the parameter, the other variable in the parameter called miles is just holding a double value of 1D. I think the problem is to do with the way my maths is being calculated. Has anyone got a clue on how I can refine this code to calculate my miles better.

private void drawPoly(SearchLocation center, Double miles)
{
//amount of vertex
double vertexCount = 100D;
         //used by the api to carried out searches
List<SearchLocation> vertices = new List<SearchLocation>();
double v = 0;
double radians = Math.PI / 180D;
double radiansPerDegree = Math.PI / 180D;
double degreePerVertex = 360D / vertexCount;
double radiansPerVertex = degreePerVertex * radiansPerDegree;
var centerOfMap = center;
const double degLatMiles = 68.68637156368D;
double degLonMiles = Math.Cos(center.Latitude.Value) * (68.68637156368D);
double milesLat = (miles * degLatMiles) / 3600;
double milesLon = (miles * degLonMiles) / 3600;
for (v = 0; v < vertexCount; v++)
{
    radians = v * radiansPerVertex;
               //adds the miles from the center point and draws a circle
    double centrLat = center.Latitude.Value + (milesLat * Math.Sin(radians));
    double centrLon = center.Longitude.Value + (milesLon * Math.Cos(radians));
    vertices.Add(new SearchLocation() { Latitude = centrLat, Longitude = centrLon });
}

Answer 1

Ok, I’ve misundestood your question. This should work :

    /// <summary>
    /// 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.
    /// </summary>
    /// <param name="source">Point of origin</param>
    /// <param name="range">Range in meters</param>
    /// <param name="bearing">Bearing in degrees</param>
    /// <returns>End-point from the source given the desired range and bearing.</returns>
    public static PointLatLng CalculateDerivedPosition(PointLatLng source, double range, double bearing)
    {
        double latA = source.Lat * DEGREES_TO_RADIANS;
        double lonA = source.Lng * DEGREES_TO_RADIANS;
        double angularDistance = range / EARTH_RADIUS_M;
        double trueCourse = bearing * DEGREES_TO_RADIANS;

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

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

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

        return new PointLatLng(
            lat / DEGREES_TO_RADIANS,
            lon / DEGREES_TO_RADIANS);
    }

Juste take your center as source :

for (int i = 0; i < 360; i++)
{
  vertices.Add(CalculateDerivedPosition(center, circleRadius, i));
}