GeographicLib 2.1.2
Static Public Member Functions | List of all members
GeographicLib::OSGB Class Reference

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

#include <GeographicLib/OSGB.hpp>

Static Public Member Functions

static void Forward (real lat, real lon, real &x, real &y, real &gamma, real &k)
 
static void Reverse (real x, real y, real &lat, real &lon, real &gamma, real &k)
 
static void Forward (real lat, real lon, real &x, real &y)
 
static void Reverse (real x, real y, real &lat, real &lon)
 
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 EquatorialRadius ()
 
static Math::real Flattening ()
 
static Math::real CentralScale ()
 
static Math::real OriginLatitude ()
 
static Math::real OriginLongitude ()
 
static Math::real FalseNorthing ()
 
static Math::real FalseEasting ()
 

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

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
#include <iostream>
#include <iomanip>
#include <exception>
#include <string>
#include <GeographicLib/OSGB.hpp>
#include <GeographicLib/DMS.hpp>
using namespace std;
using namespace GeographicLib;
int main() {
try {
{
// Sample forward calculation from
// A guide to coordinate systems in Great Britain
double
lat = DMS::Decode(52,39,27.2531),
lon = DMS::Decode( 1,43, 4.5177);
double x, y;
OSGB::Forward(lat, lon, x, y);
string gridref;
OSGB::GridReference(x, y, 2, gridref);
cout << fixed << setprecision(3)
<< x << " " << y << " " << gridref << "\n";
}
{
// Sample reverse calculation
string gridref = "TG5113";
double x, y;
int prec;
OSGB::GridReference(gridref, x, y, prec);
double lat, lon;
OSGB::Reverse(x, y, lat, lon);
cout << fixed << setprecision(8)
<< prec << " " << lat << " " << lon << "\n";
}
}
catch (const exception& e) {
cerr << "Caught exception: " << e.what() << "\n";
return 1;
}
}
main
int main(int argc, const char *const argv[])
Definition: CartConvert.cpp:29
DMS.hpp
Header for GeographicLib::DMS class.
OSGB.hpp
Header for GeographicLib::OSGB class.
GeographicLib::DMS::Decode
static Math::real Decode(const std::string &dms, flag &ind)
Definition: DMS.cpp:40
GeographicLib::OSGB::GridReference
static void GridReference(real x, real y, int prec, std::string &gridref)
Definition: OSGB.cpp:39
GeographicLib::OSGB::Forward
static void Forward(real lat, real lon, real &x, real &y, real &gamma, real &k)
Definition: OSGB.hpp:93
GeographicLib::OSGB::Reverse
static void Reverse(real x, real y, real &lat, real &lon, real &gamma, real &k)
Definition: OSGB.hpp:114
GeographicLib
Namespace for GeographicLib.
Definition: Accumulator.cpp:12

Definition at line 44 of file OSGB.hpp.

Member Function Documentation

◆ Forward() [1/2]

static void GeographicLib::OSGB::Forward ( real  lat,
real  lon,
real &  x,
real &  y,
real &  gamma,
real &  k 
)
inlinestatic

Forward projection, from geographic to OSGB coordinates.

Parameters
[in]latlatitude of point (degrees).
[in]lonlongitude of point (degrees).
[out]xeasting of point (meters).
[out]ynorthing of point (meters).
[out]gammameridian convergence at point (degrees).
[out]kscale of projection at point.

lat should be in the range [−90°, 90°].

Definition at line 93 of file OSGB.hpp.

References GeographicLib::TransverseMercator::Forward().

◆ Reverse() [1/2]

static void GeographicLib::OSGB::Reverse ( real  x,
real  y,
real &  lat,
real &  lon,
real &  gamma,
real &  k 
)
inlinestatic

Reverse projection, from OSGB coordinates to geographic.

Parameters
[in]xeasting of point (meters).
[in]ynorthing of point (meters).
[out]latlatitude of point (degrees).
[out]lonlongitude of point (degrees).
[out]gammameridian convergence at point (degrees).
[out]kscale of projection at point.

The value of lon returned is in the range [−180°, 180°].

Definition at line 114 of file OSGB.hpp.

References GeographicLib::TransverseMercator::Reverse().

◆ Forward() [2/2]

static void GeographicLib::OSGB::Forward ( real  lat,
real  lon,
real &  x,
real &  y 
)
inlinestatic

OSGB::Forward without returning the convergence and scale.

Definition at line 124 of file OSGB.hpp.

◆ Reverse() [2/2]

static void GeographicLib::OSGB::Reverse ( real  x,
real  y,
real &  lat,
real &  lon 
)
inlinestatic

OSGB::Reverse without returning the convergence and scale.

Definition at line 132 of file OSGB.hpp.

◆ GridReference() [1/2]

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

Convert OSGB coordinates to a grid reference.

Parameters
[in]xeasting of point (meters).
[in]ynorthing of point (meters).
[in]precprecision relative to 100 km.
[out]gridrefNational Grid reference.
Exceptions
GeographicErrif prec, x, or y is outside its allowed range.
std::bad_allocif the memory for gridref can't be allocatied.

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), 1μm

The easting must be in the range [−1000 km, 1500 km) and the northing must be in the range [−500 km, 2000 km). These bounds are consistent with rules for the letter designations for the grid system.

If x or y is NaN, the returned grid reference is "INVALID".

Definition at line 39 of file OSGB.cpp.

References GeographicLib::Utility::str().

◆ GridReference() [2/2]

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

Convert OSGB grid reference to coordinates.

Parameters
[in]gridrefNational Grid reference.
[out]xeasting of point (meters).
[out]ynorthing of point (meters).
[out]precprecision relative to 100 km.
[in]centerpif true (default), return center of the grid square, else return SW (lower left) corner.
Exceptions
GeographicErrif gridref is illegal.

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

If the first 2 characters of gridref are "IN", then x and y are set to NaN and prec is set to −2.

Definition at line 93 of file OSGB.cpp.

References GeographicLib::Utility::lookup(), and GeographicLib::Math::NaN().

◆ EquatorialRadius()

static Math::real GeographicLib::OSGB::EquatorialRadius ( )
inlinestatic
Returns
a the equatorial radius of the Airy 1830 ellipsoid (meters).

This is 20923713 ft converted to meters using the rule 1 ft = 109.48401603−10 m. The Airy 1830 value is returned because the OSGB projection is based on this ellipsoid. The conversion factor from feet to meters is the one used for the 1936 retriangulation of Britain; see Section A.1 (footnote 10 on p. 44) of A guide to coordinate systems in Great Britain, v3.6 (2020).

Definition at line 202 of file OSGB.hpp.

◆ Flattening()

static Math::real GeographicLib::OSGB::Flattening ( )
inlinestatic
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 217 of file OSGB.hpp.

◆ CentralScale()

static Math::real GeographicLib::OSGB::CentralScale ( )
inlinestatic
Returns
k0 central scale for the OSGB projection (0.9996012717...).

C. J. Mugnier, Grids & Datums, PE&RS, Oct. 2003, states that this is defined as 109.9998268−10.

Definition at line 226 of file OSGB.hpp.

◆ OriginLatitude()

static Math::real GeographicLib::OSGB::OriginLatitude ( )
inlinestatic
Returns
latitude of the origin for the OSGB projection (49 degrees).

Definition at line 234 of file OSGB.hpp.

◆ OriginLongitude()

static Math::real GeographicLib::OSGB::OriginLongitude ( )
inlinestatic
Returns
longitude of the origin for the OSGB projection (−2 degrees).

Definition at line 240 of file OSGB.hpp.

◆ FalseNorthing()

static Math::real GeographicLib::OSGB::FalseNorthing ( )
inlinestatic
Returns
false northing the OSGB projection (−100000 meters).

Definition at line 245 of file OSGB.hpp.

◆ FalseEasting()

static Math::real GeographicLib::OSGB::FalseEasting ( )
inlinestatic
Returns
false easting the OSGB projection (400000 meters).

Definition at line 250 of file OSGB.hpp.

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