/// <summary>
/// Computes the reverse transformation.
/// </summary>
/// <param name="coordinate">The coordinate.</param>
/// <returns>The transformed coordinate.</returns>
protected override GeoCoordinate ComputeReverse(String coordinate)
{
// source: http://en.wikipedia.org/wiki/MGRS
if (coordinate == null)
{
throw new ArgumentNullException("coordinate", "The coordinate is null.");
}
if (!Regex.IsMatch(coordinate, "^[0-9]{1,2}[A-Z]{1,3}[0-9]{2,10}"))
{
throw new ArgumentException("The coordinate is not a valid MGRS string.", "coordinate");
}
Int32 xZoneNumber = 0, yZoneNumber = 0, columnNumber = 0, rowNumber = 0, columnMeters = 0, rowMeters = 0, precision = 0;
// compute the main zone
if (Regex.IsMatch(coordinate, "^[0-9]{1,2}[A-Z]{1}"))
{
if (Char.IsDigit(coordinate[1]))
{
xZoneNumber = Int32.Parse(coordinate.Substring(0, 2));
yZoneNumber = _gridSigns.IndexOf(coordinate[2]);
}
else
{
xZoneNumber = Int32.Parse(coordinate.Substring(0, 1));
yZoneNumber = _gridSigns.IndexOf(coordinate[1]);
}
}
// compute the latitude and longitude for the main zone
Double longitudeBase = (xZoneNumber - 1) * _zoneWidth - Constants.PI;
Double latitudeBase = (yZoneNumber - 2) * _zoneHeight - 80 * Constants.DegreeToRadian;
// compute the subzone
if (Regex.IsMatch(coordinate, "^[0-9]{1,2}[A-Z]{3}"))
{
if (xZoneNumber >= 10)
{
columnNumber = _columnSigns.IndexOf(coordinate[3]); // compute the relative row and column
rowNumber = _rowSigns.IndexOf(coordinate[4]);
}
else
{
columnNumber = _columnSigns.IndexOf(coordinate[2]);
rowNumber = _rowSigns.IndexOf(coordinate[3]);
}
}
// compute metre precision
if (Regex.IsMatch(coordinate, "^[0-9]{1,2}[A-Z]{1,3}[0-9]{2,10}"))
{
if (xZoneNumber >= 10)
{
if ((coordinate.Length - 5) % 2 != 0)
{
throw new ArgumentException("The coordinate is not a valid MGRS string.", "coordinate");
}
precision = (coordinate.Length - 5) / 2;
columnMeters = Int32.Parse(coordinate.Substring(5, precision)) * Convert.ToInt32(Calculator.Pow(10, 5 - precision));
rowMeters = Int32.Parse(coordinate.Substring(5 + precision, precision)) * Convert.ToInt32(Calculator.Pow(10, 5 - precision));
}
else
{
if ((coordinate.Length - 4) % 2 != 0)
{
throw new ArgumentException("The coordinate is not a valid MGRS string.", "coordinate");
}
precision = (coordinate.Length - 4) / 2;
columnMeters = Int32.Parse(coordinate.Substring(4, precision)) * Convert.ToInt32(Calculator.Pow(10, 5 - precision));
rowMeters = Int32.Parse(coordinate.Substring(4 + precision, precision)) * Convert.ToInt32(Calculator.Pow(10, 5 - precision));
}
}
CoordinateProjection projection = CoordinateProjectionFactory.UniversalTransverseMercatorZone(Ellipsoids.WGS1984, xZoneNumber, latitudeBase >= 0 ? EllipsoidHemisphere.North : EllipsoidHemisphere.South);
Coordinate coordinateBase = projection.Forward(new GeoCoordinate(latitudeBase, longitudeBase));
// row number correction
if (xZoneNumber % 2 == 0)
{
rowNumber = (rowNumber + _rowSigns.Count - 5) % _rowSigns.Count;
}
Int32 rowNumberBase = Convert.ToInt32(Math.Floor(coordinateBase.Y / _rowHeight));
// compute the number inside the zone
if (rowNumberBase / _rowSigns.Count * _rowSigns.Count + rowNumber < rowNumberBase)
{
rowNumber += (rowNumberBase / _rowSigns.Count + 1) * _rowSigns.Count;
}
else
{
rowNumber += rowNumberBase / _rowSigns.Count * _rowSigns.Count;
}
if (rowNumber >= 190) // handle overflow
{
rowNumber -= _rowSigns.Count;
}
// compute metre precision
Double coordinateX = (columnNumber % 8 + 1) * _columnWidth + columnMeters;
Double coordinateY = rowNumber * _rowHeight + rowMeters;
// apply projection
return(projection.Reverse(new Coordinate(coordinateX, coordinateY)));
}
