/// <summary>
/// Creates a ruler object from tile coordinates.
/// </summary>
/// <param name="y">Y TileId</param>
/// <param name="z">Zoom Level</param>
/// <param name="units"></param>
/// <returns></returns>
public static CheapRuler FromTile(int y, int z, CheapRulerUnits units = CheapRulerUnits.Kilometers)
{
var n = Math.PI * (1 - 2 * (y + 0.5) / Math.Pow(2, z));
var lat = Math.Atan(0.5 * (Math.Exp(n) - Math.Exp(-n))) * 180 / Math.PI;
return(new CheapRuler(lat, units));
}
/// <summary>
/// Creates a ruler object that will approximate measurements around the given latitude. Units are one of: kilometers
/// </summary>
/// <param name="outputUnits"></param>
public CheapRuler(double latitude, CheapRulerUnits outputUnits = CheapRulerUnits.Kilometers)
{
double factor;
switch (outputUnits)
{
case CheapRulerUnits.Kilometers:
factor = 1.0d;
break;
case CheapRulerUnits.Miles:
factor = 1000.0d / 1609.344;
break;
case CheapRulerUnits.NauticalMiles:
factor = 1000.0d / 1852.0d;
break;
case CheapRulerUnits.Meters:
factor = 1000.0d;
break;
case CheapRulerUnits.Yards:
factor = 1000.0d / 0.9144;
break;
case CheapRulerUnits.Feet:
factor = 1000.0d / 0.3048;
break;
case CheapRulerUnits.Inches:
factor = 1000.0d / 0.0254;
break;
default:
factor = 1.0d;
break;
}
var cos = Math.Cos(latitude * Math.PI / 180);
var cos2 = 2 * cos * cos - 1;
var cos3 = 2 * cos * cos2 - cos;
var cos4 = 2 * cos * cos3 - cos2;
var cos5 = 2 * cos * cos4 - cos3;
// multipliers for converting longitude and latitude degrees into distance (http://1.usa.gov/1Wb1bv7)
_kx = factor * (111.41513 * cos - 0.09455 * cos3 + 0.00012 * cos5);
_ky = factor * (111.13209 - 0.56605 * cos2 + 0.0012 * cos4);
}
