// converts lat and lon (OSGB36) to OS 6 figure northing and easting
private void Initialise(LatLonCoord coord)
{
// Debug.Assert(coord.Elipsoid == CoordSystem.OSGB36);
double lat = coord.Latitude;
double lon = coord.Longitude;
double phi = Math.DegToRad(lat); // convert latitude to radians
double lam = Math.DegToRad(lon); // convert longitude to radians
double a = 6377563.396; // OSGB semi-major axis
double b = 6356256.91; // OSGB semi-minor axis
double e0 = 400000; // easting of false origin
double n0 = -100000; // northing of false origin
double f0 = 0.9996012717; // OSGB scale factor on central meridian
double e2 = 0.0066705397616; // OSGB eccentricity squared
double lam0 = -0.034906585039886591; // OSGB false east
double phi0 = 0.85521133347722145; // OSGB false north
double af0 = a * f0;
double bf0 = b * f0;
// easting
double slat2 = Math.Sin(phi) * Math.Sin(phi);
double nu = af0 / (Math.Sqrt(1 - (e2 * (slat2))));
double rho = (nu * (1 - e2)) / (1 - (e2 * slat2));
double eta2 = (nu / rho) - 1;
double p = lam - lam0;
double IV = nu * Math.Cos(phi);
double clat3 = Math.Pow(Math.Cos(phi), 3);
double tlat2 = Math.Tan(phi) * Math.Tan(phi);
double V = (nu / 6) * clat3 * ((nu / rho) - tlat2);
double clat5 = Math.Pow(Math.Cos(phi), 5);
double tlat4 = Math.Pow(Math.Tan(phi), 4);
double VI = (nu / 120) * clat5 * ((5 - (18 * tlat2)) + tlat4 + (14 * eta2) - (58 * tlat2 * eta2));
double east = e0 + (p * IV) + (Math.Pow(p, 3) * V) + (Math.Pow(p, 5) * VI);
// northing
double n = (af0 - bf0) / (af0 + bf0);
double M = Marc(bf0, n, phi0, phi);
double I = M + (n0);
double II = (nu / 2) * Math.Sin(phi) * Math.Cos(phi);
double III = ((nu / 24) * Math.Sin(phi) * Math.Pow(Math.Cos(phi), 3)) * (5 - Math.Pow(Math.Tan(phi), 2) + (9 * eta2));
double IIIA = ((nu / 720) * Math.Sin(phi) * clat5) * (61 - (58 * tlat2) + tlat4);
double north = I + ((p * p) * II) + (Math.Pow(p, 4) * III) + (Math.Pow(p, 6) * IIIA);
// make whole number values
east = Math.Round(east); // round to whole number
north = Math.Round(north); // round to whole number
// convert to nat grid ref
Eastings = east;
Northings = north;
}
internal NmeaFixMessage(
DateTime time,
LatLonCoord coords,
double altitude, // Above sea level
FixQuality quality,
int sateliteCount)
{
this.Time = time;
this.Coords = coords;
this.Altitude = altitude;
this.Quality = quality;
this.SateliteCount = sateliteCount;
}
public OSGBGridRef(LatLonCoord coord)
{
// Debug.Assert(coord.Elipsoid == CoordSystem.OSGB36);
Initialise(coord);
}
// Processes WGS84 lat and lon in decimal form with S and W as -ve
private static LatLonCoord WGS84ToOSGB36(LatLonCoord coord)
{
// Debug.Assert(coord.Elipsoid == CoordSystem.WGS84);
double WGlat = coord.Latitude;
double WGlon = coord.Longitude;
double height = coord.Altitude;
//first off convert to radians
double radWGlat = Math.DegToRad(WGlat);
double radWGlon = Math.DegToRad(WGlon);
/* these calculations were derived from the work of
* Roger Muggleton (http://www.carabus.co.uk/) */
/* quoting Roger Muggleton :-
* There are many ways to convert data from one system to another, the most accurate
* being the most complex! For this example I shall use a 7 parameter Helmert
* transformation.
* The process is in three parts:
* (1) Convert latitude and longitude to Cartesian coordinates (these also include height
* data, and have three parameters, X, Y and Z).
* (2) Transform to the new system by applying the 7 parameters and using a little maths.
* (3) Convert back to latitude and longitude.
* For the example we shall transform a GRS80 location to Airy, e.g. a GPS reading to
* the Airy spheroid.
* The following code converts latitude and longitude to Cartesian coordinates. The
* input parameters are: WGS84 latitude and longitude, axis is the GRS80/WGS84 major
* axis in metres, ecc is the eccentricity, and height is the height above the
* ellipsoid.
* v = axis / (Math.sqrt (1 - ecc * (Math.Pow (Math.sin(lat), 2))));
* x = (v + height) * Math.cos(lat) * Math.cos(lon);
* y = (v + height) * Math.cos(lat) * Math.sin(lon);
* z = ((1 - ecc) * v + height) * Math.sin(lat);
* The transformation requires the 7 parameters: xp, yp and zp correct the coordinate
* origin, xr, yr and zr correct the orientation of the axes, and sf deals with the
* changing scale factors. */
//these are the values for WGS86(GRS80) to OSGB36(Airy)
double h = height; // height above datum (from GPS GGA sentence)
const double a = 6378137; // WGS84_AXIS
const double e = 0.00669438037928458; // WGS84_ECCENTRIC
const double a2 = 6377563.396; //OSGB_AXIS
const double e2 = 0.0066705397616; // OSGB_ECCENTRIC
const double xp = -446.448;
const double yp = 125.157;
const double zp = -542.06;
const double xr = -0.1502;
const double yr = -0.247;
const double zr = -0.8421;
const double s = 20.4894;
// convert to cartesian; lat, lon are radians
double sf = s * 0.000001;
double v = a / (Math.Sqrt(1 - (e * (Math.Sin(radWGlat) * Math.Sin(radWGlat)))));
double x = (v + h) * Math.Cos(radWGlat) * Math.Cos(radWGlon);
double y = (v + h) * Math.Cos(radWGlat) * Math.Sin(radWGlon);
double z = ((1 - e) * v + h) * Math.Sin(radWGlat);
// transform cartesian
double xrot = Math.DegToRad(xr / 3600);
double yrot = Math.DegToRad(yr / 3600);
double zrot = Math.DegToRad(zr / 3600);
double hx = x + (x * sf) - (y * zrot) + (z * yrot) + xp;
double hy = (x * zrot) + y + (y * sf) - (z * xrot) + yp;
double hz = (-1 * x * yrot) + (y * xrot) + z + (z * sf) + zp;
// Convert back to lat, lon
double newLon = Math.Atan(hy / hx);
double p = Math.Sqrt((hx * hx) + (hy * hy));
double newLat = Math.Atan(hz / (p * (1 - e2)));
v = a2 / (Math.Sqrt(1 - e2 * (Math.Sin(newLat) * Math.Sin(newLat))));
double errvalue = 1.0;
double lat0 = 0;
while (errvalue > 0.001)
{
lat0 = Math.Atan((hz + e2 * v * Math.Sin(newLat)) / p);
errvalue = Math.Abs(lat0 - newLat);
newLat = lat0;
}
//convert back to degrees
newLat = Math.RadToDeg(newLat);
newLon = Math.RadToDeg(newLon);
return new LatLonCoord(newLat, newLon, height, CoordSystem.OSGB36);
}
public bool IsEqualTo(LatLonCoord coord)
{
return (coord != null) &&
(this.Latitude == coord.Latitude) &&
(this.Longitude == coord.Longitude) &&
(this.Altitude == coord.Altitude) &&
(this.Elipsoid == coord.Elipsoid);
}
public static LatLonCoord Convert(
LatLonCoord sourceCoord,
CoordSystem targetElipsoid)
{
if ((sourceCoord.Elipsoid == CoordSystem.WGS84) && (targetElipsoid == CoordSystem.OSGB36))
{
return WGS84ToOSGB36(sourceCoord);
}
throw new NotImplementedException("Conversion not supported");;
}
// 5325.5117,N,00213.9296,W = +53° 25.5117', -02° 13.9296'
private static LatLonCoord DecodePositionelement(
string latitudeDeg,
string latitudeMin,
string longitudeDeg,
string longitudeMin,
string altitudeAboveMeanSeaLevel,
string heightOfMeanSeaLevelAboveElipsoid)
{
int latDegrees = (int)(double)double.Parse(latitudeDeg.Substring(0, 2));
double latMinutes = (double)double.Parse(latitudeDeg.Substring(2));
if (latitudeMin == "S") // TODO: Better validation needed.
latDegrees = -latDegrees;
int lonDegrees = (int)(double)double.Parse(longitudeDeg.Substring(0, 3));
double lonMinutes = (double)double.Parse(longitudeDeg.Substring(3));
if (longitudeMin == "W") // TODO: Better validation needed.
lonDegrees = -lonDegrees;
double altitudeAboveElipsoid = (double)double.Parse(altitudeAboveMeanSeaLevel) + (double)double.Parse(heightOfMeanSeaLevelAboveElipsoid);
LatLonCoord ll = new LatLonCoord(latDegrees, latMinutes, lonDegrees, lonMinutes, altitudeAboveElipsoid,
CoordSystem.WGS84);
return ll;
}
