Functions to convert between web mercator and geographic coordinates.

WebMercatorGeographicConversion.cs

// from http://www.gal-systems.com/2011/07/convert-coordinates-between-web.html

private void ToGeographic(ref double mercatorX_lon, ref double mercatorY_lat)
{
	if (Math.Abs(mercatorX_lon) < 180 && Math.Abs(mercatorY_lat) < 90)
		return;

	if ((Math.Abs(mercatorX_lon) > 20037508.3427892) || (Math.Abs(mercatorY_lat) > 20037508.3427892))
		return;

	double x = mercatorX_lon;
	double y = mercatorY_lat;
	double num3 = x / 6378137.0;
	double num4 = num3 * 57.295779513082323;
	double num5 = Math.Floor((double)((num4 + 180.0) / 360.0));
	double num6 = num4 - (num5 * 360.0);
	double num7 = 1.5707963267948966 - (2.0 * Math.Atan(Math.Exp((-1.0 * y) / 6378137.0)));
	mercatorX_lon = num6;
	mercatorY_lat = num7 * 57.295779513082323;
}

private void ToWebMercator(ref double mercatorX_lon, ref double mercatorY_lat)
{
	if ((Math.Abs(mercatorX_lon) > 180 || Math.Abs(mercatorY_lat) > 90))
		return;

	double num = mercatorX_lon * 0.017453292519943295;
	double x = 6378137.0 * num;
	double a = mercatorY_lat * 0.017453292519943295;

	mercatorX_lon = x;
	mercatorY_lat = 3189068.5 * Math.Log((1.0 + Math.Sin(a)) / (1.0 - Math.Sin(a)));
}