GeographicLib::OSGB Class Reference

Ordnance Survey grid system for Great Britain. More...

#include <GeographicLib/OSGB.hpp>

List of all members.

Static Public Member Functions
static void	Forward (real lat, real lon, real &x, real &y, real &gamma, real &k) throw ()
static void	Reverse (real x, real y, real &lat, real &lon, real &gamma, real &k) throw ()
static void	Forward (real lat, real lon, real &x, real &y) throw ()
static void	Reverse (real x, real y, real &lat, real &lon) throw ()
static void	GridReference (real x, real y, int prec, std::string &gridref)
static void	GridReference (const std::string &gridref, real &x, real &y, int &prec, bool centerp=true)
Inspector functions
static Math::real	MajorRadius () throw ()
static Math::real	Flattening () throw ()
static Math::real	CentralScale () throw ()
static Math::real	OriginLatitude () throw ()
static Math::real	OriginLongitude () throw ()
static Math::real	FalseNorthing () throw ()
static Math::real	FalseEasting () throw ()

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Detailed Description

Ordnance Survey grid system for Great Britain.

The class implements the coordinate system used by the Ordnance Survey for maps of Great Britain and conversions to the grid reference system.

See

• A guide to coordinate systems in Great Britain
• Guide to National Grid

WARNING: the latitudes and longitudes for the Ordnance Survey grid system do not use the WGS84 datum. Do not use the values returned by this class in the UTMUPS, MGRS, or Geoid classes without first converting the datum (and vice versa).

Example of use:

// Example of using the GeographicLib::OSGB class
// $Id: 80feea12c2ebb7e594d8e17bf841c1a141cf3c36 $

#include <iostream>
#include <exception>
#include <string>
#include <GeographicLib/OSGB.hpp>

using namespace std;
using namespace GeographicLib;

int main() {
  try {
    {
      // Sample forward calculation
      double lat = 55.5, lon = -1.64; // Embleton, Northumberland
      double x, y;
      OSGB::Forward(lat, lon, x, y);
      string gridref;
      OSGB::GridReference(x, y, 2, gridref);
      cout << x << " " << y << " " << gridref << "\n";
    }
    {
      // Sample reverse calculation
      string gridref = "NU2222";
      double x, y;
      int prec;
      OSGB::GridReference(gridref, x, y, prec);
      double lat, lon;
      OSGB::Reverse(x, y, lat, lon);
      cout << prec << " " << lat << " " << lon << "\n";
    }
  }
  catch (const exception& e) {
    cerr << "Caught exception: " << e.what() << "\n";
    return 1;
  }
  return 0;
}

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Member Function Documentation

static void GeographicLib::OSGB::Forward	(	real	lat,
		real	lon,
		real &	x,
		real &	y,
		real &	gamma,
		real &	k
	)		throw () [inline, static]

Forward projection, from geographic to OSGB coordinates.

Parameters:

[in]	lat	latitude of point (degrees).
[in]	lon	longitude of point (degrees).
[out]	x	easting of point (meters).
[out]	y	northing of point (meters).
[out]	gamma	meridian convergence at point (degrees).
[out]	k	scale of projection at point.

lat should be in the range [-90, 90]; lon and lon0 should be in the range [-180, 360].

Definition at line 86 of file OSGB.hpp.

static void GeographicLib::OSGB::Reverse	(	real	x,
		real	y,
		real &	lat,
		real &	lon,
		real &	gamma,
		real &	k
	)		throw () [inline, static]

Reverse projection, from OSGB coordinates to geographic.

Parameters:

[in]	x	easting of point (meters).
[in]	y	northing of point (meters).
[out]	lat	latitude of point (degrees).
[out]	lon	longitude of point (degrees).
[out]	gamma	meridian convergence at point (degrees).
[out]	k	scale of projection at point.

The value of lon returned is in the range [-180, 180).

Definition at line 106 of file OSGB.hpp.

static void GeographicLib::OSGB::Forward	(	real	lat,
		real	lon,
		real &	x,
		real &	y
	)		throw () [inline, static]

OSGB::Forward without returning the convergence and scale.

Definition at line 116 of file OSGB.hpp.

static void GeographicLib::OSGB::Reverse	(	real	x,
		real	y,
		real &	lat,
		real &	lon
	)		throw () [inline, static]

OSGB::Reverse without returning the convergence and scale.

Definition at line 124 of file OSGB.hpp.

void GeographicLib::OSGB::GridReference	(	real	x,
		real	y,
		int	prec,
		std::string &	gridref
	)		[static]

Convert OSGB coordinates to a grid reference.

Parameters:

[in]	x	easting of point (meters).
[in]	y	northing of point (meters).
[in]	prec	precision relative to 100 km.
[out]	gridref	National Grid reference.

prec specifies the precision of the grid reference string as follows:

• prec = 0 (min), 100km
• prec = 1, 10km
• prec = 2, 1km
• prec = 3, 100m
• prec = 4, 10m
• prec = 5, 1m
• prec = 6, 0.1m
• prec = 11 (max), 1um

The easting must be in the range [-1000 km, 1500 km) and the northing must be in the range [-500 km, 2000 km). An exception is thrown if either the easting and northing is outside these bounds. These bounds are consistent with rules for the letter designations for the grid system.

Definition at line 36 of file OSGB.cpp.

void GeographicLib::OSGB::GridReference	(	const std::string &	gridref,
		real &	x,
		real &	y,
		int &	prec,
		bool	centerp = true
	)		[static]

Convert OSGB coordinates to a grid reference.

Parameters:

[in]	gridref	National Grid reference.
[out]	x	easting of point (meters).
[out]	y	northing of point (meters).
[out]	prec	precision relative to 100 km.
[in]	centerp	if true (default), return center of the grid square, else return SW (lower left) corner.

The grid reference must be of the form: two letters (not including I) followed by an even number of digits (up to 22).

Definition at line 84 of file OSGB.cpp.

static Math::real GeographicLib::OSGB::MajorRadius

(

)

throw () [inline, static]

Returns:

a the equatorial radius of the Airy 1830 ellipsoid (meters).

This is 20923713 ft converted to meters using the rule 1 ft = 10^(9.48401603-10) m. (The Airy 1830 value is returned because the OSGB projection is based on this ellipsoid.)

Definition at line 182 of file OSGB.hpp.

static Math::real GeographicLib::OSGB::Flattening

(

)

throw () [inline, static]

Returns:

f the inverse flattening of the Airy 1830 ellipsoid.

For the Airy 1830 ellipsoid, a = 20923713 ft and b = 20853810 ft; thus the flattening = (20923713 - 20853810)/20923713 = 7767/2324857 = 1/299.32496459... (The Airy 1830 value is returned because the OSGB projection is based on this ellipsoid.)

Definition at line 194 of file OSGB.hpp.

static Math::real GeographicLib::OSGB::CentralScale

(

)

throw () [inline, static]

Returns:

k0 central scale for the OSGB projection (0.9996012717).

Definition at line 208 of file OSGB.hpp.

static Math::real GeographicLib::OSGB::OriginLatitude

(

)

throw () [inline, static]

Returns:

latitude of the origin for the OSGB projection (49 degrees).

Definition at line 214 of file OSGB.hpp.

static Math::real GeographicLib::OSGB::OriginLongitude

(

)

throw () [inline, static]

Returns:

longitude of the origin for the OSGB projection (-2 degrees).

Definition at line 219 of file OSGB.hpp.

static Math::real GeographicLib::OSGB::FalseNorthing

(

)

throw () [inline, static]

Returns:

false northing the OSGB projection (-100000 meters).

Definition at line 224 of file OSGB.hpp.

static Math::real GeographicLib::OSGB::FalseEasting

(

)

throw () [inline, static]

Returns:

false easting the OSGB projection (400000 meters).

Definition at line 229 of file OSGB.hpp.

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The documentation for this class was generated from the following files:

• OSGB.hpp
• OSGB.cpp