how to draw offline circle of 1500 meters range over the geocoordinate in windows phone 8

Question

I want draw the offline circle over the geocoordinate in windows phone this circle is of 1500 meter range and it search the target within this range

this my image where i have point to draw circle using width and heigth but i want to draw circle using radius while i zoom, the range of the circle also affected

and also search the target within this range or not

    //  double metersPerPixels = (Math.Cos(geo.Latitude * Math.PI / 180) * 2 * Math.PI * 6378137) / (256 * Math.Pow(2, map.ZoomLevel));
    // double radius = 1000 / metersPerPixels;



    map.Layers.Add(new MapLayer()
          {
            new MapOverlay()
            {
                GeoCoordinate = geo,                   
                PositionOrigin = new Point(0.5,0.5),   
                 Content = new Ellipse
                {   

                    Opacity=.4,
                    Fill = new SolidColorBrush(color),
                    Width = 100,//radius * 2 
                    Height =100 //adius * 2 

                }
             }                
          });

Answer 1

Here you go, you can use it with your own class by changing the Location class in this helper.

Here is the sample helper to create a circle out of the initializing point and radius in meter:

/// <summary>
/// The geo drawing helper.
/// </summary>
public class GeoDrawingHelper
{
    #region Constants

    /// <summary>
    /// The c_ earth radius in kilometers.
    /// </summary>
    public const double c_EarthRadiusInKilometers = 6367.0;

    #endregion

    #region Public Methods and Operators

    /// <summary>
    /// Creates a circle by the initializing point.
    /// </summary>
    /// <param name="center">
    /// The center Point.
    /// </param>
    /// <param name="radius">
    /// The radius in meter.
    /// </param>
    /// <returns>
    /// The <see cref="List"/>.
    /// </returns>
    public static List<Location> CreateCirclePoints(Location center, double radius)
    {
        double lat = ToRadian(center.Latitude); // radians
        double lng = ToRadian(center.Longitude); // radians
        double d = radius / (c_EarthRadiusInKilometers * 1000); // d = angular distance covered on earth's surface
        var locations = new List<Location>();

        for (var x = 0; x <= 360; x++)
        {
            // Calculate the coordinates of the point
            double brng = ToRadian(x);
            double latRadians = Math.Asin((Math.Sin(lat) * Math.Cos(d)) + (Math.Cos(lat) * Math.Sin(d) * Math.Cos(brng)));
            double lngRadians = lng
                                + Math.Atan2(
                                    Math.Sin(brng) * Math.Sin(d) * Math.Cos(lat), 
                                    Math.Cos(d) - (Math.Sin(lat) * Math.Sin(latRadians)));

            // Add the location
            locations.Add(new Location() { Latitude = ToDegrees(latRadians), Longitude = ToDegrees(lngRadians) });
        }

        return locations;
    }

    /// <summary>
    /// Convert the radian to degrees measure.
    /// </summary>
    /// <param name="radians">
    /// The radians.
    /// </param>
    /// <returns>
    /// The <see cref="double"/>.
    /// </returns>
    public static double ToDegrees(double radians)
    {
        return radians * (180 / Math.PI);
    }

    /// <summary>
    /// Convert the degrees to radian measure.
    /// </summary>
    /// <param name="degrees">
    /// The degrees.
    /// </param>
    /// <returns>
    /// The <see cref="double"/>.
    /// </returns>
    public static double ToRadian(double degrees)
    {
        return degrees * (Math.PI / 180);
    }

    #endregion
}

Answer 2

To prevent elipses on sertain latitudes I use the following code:

// Function to draw circle on map:

private void DrawCircle(BasicGeoposition CenterPosition, int Radius)
    {
    Color FillColor = Colors.Purple;
    Color StrokeColor = Colors.Red;
    FillColor.A = 80;
    StrokeColor.A = 80;
    Circle = new MapPolygon
        {
            StrokeThickness = 2,
            FillColor = FillColor,
            StrokeColor = StrokeColor,
            Path = new Geopath(Functions.CalculateCircle(CenterPosition, Radius))
        };
    mpBingMaps.MapElements.Add(Circle);
}

// Constants and helper functions:

const double earthRadius = 6371000D;
const double Circumference = 2D * Math.PI * earthRadius;

public static List<BasicGeoposition> CalculateCircle(BasicGeoposition Position, double Radius)
{
    List<BasicGeoposition> GeoPositions = new List<BasicGeoposition>();
    for (int i = 0; i <= 360; i++)
    {
        double Bearing = ToRad(i);
        double CircumferenceLatitudeCorrected = 2D * Math.PI * Math.Cos(ToRad(Position.Latitude)) * earthRadius;
        double lat1 = Circumference / 360D * Position.Latitude;
        double lon1 = CircumferenceLatitudeCorrected / 360D * Position.Longitude;
        double lat2 = lat1 + Math.Sin(Bearing) * Radius;
        double lon2 = lon1 + Math.Cos(Bearing) * Radius;
        BasicGeoposition NewBasicPosition = new BasicGeoposition();
        NewBasicPosition.Latitude = lat2 / (Circumference / 360D);
        NewBasicPosition.Longitude = lon2 / (CircumferenceLatitudeCorrected / 360D);
        GeoPositions.Add(NewBasicPosition);
    }
    return GeoPositions;
}

private static double ToRad(double degrees)
{
    return degrees * (Math.PI / 180D);
}

This code is usefull for small radius of less than a few miles.