GeographicLib 2.7

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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

- A guide to coordinate systems in Great Britain
- Using the 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
#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 Cart3Convert.cpp:52
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:34
GeographicLib::OSGB::Forward
static void Forward(real lat, real lon, real &x, real &y, real &gamma, real &k)
Definition OSGB.hpp:73
GeographicLib::OSGB::Reverse
static void Reverse(real x, real y, real &lat, real &lon, real &gamma, real &k)
Definition OSGB.hpp:94
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12
std
Definition NearestNeighbor.hpp:806

Definition at line 38 of file OSGB.hpp.

## Member Function Documentation

## ◆ Forward() [1/2]

void GeographicLib::OSGB::Forward | ( | real | lat,
|  | real | lon,
|  | real & | x,
|  | real & | y,
|  | real & | gamma,
|  | real & | k )
| 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°].

Definition at line 73 of file OSGB.hpp.

References FalseEasting(), and OriginLongitude().

Referenced by Forward().

## ◆ Reverse() [1/2]

void GeographicLib::OSGB::Reverse | ( | real | x,
|  | real | y,
|  | real & | lat,
|  | real & | lon,
|  | real & | gamma,
|  | real & | k )
| 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 94 of file OSGB.hpp.

References FalseEasting(), and OriginLongitude().

Referenced by Reverse().

## ◆ Forward() [2/2]

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

OSGB::Forward without returning the convergence and scale.

Definition at line 104 of file OSGB.hpp.

References Forward().

## ◆ Reverse() [2/2]

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

OSGB::Reverse without returning the convergence and scale.

Definition at line 112 of file OSGB.hpp.

References Reverse().

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

Exceptions

  GeographicErr | if prec, x, or y is outside its allowed range.
  std::bad_alloc | if 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 34 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] | 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.

Exceptions

  GeographicErr | if 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 87 of file OSGB.cpp.

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

## ◆ EquatorialRadius()

Math::real GeographicLib::OSGB::EquatorialRadius | ( |  | ) |
| 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 = 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 182 of file OSGB.hpp.

## ◆ Flattening()

Math::real GeographicLib::OSGB::Flattening | ( |  | ) |
| 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 197 of file OSGB.hpp.

## ◆ CentralScale()

Math::real GeographicLib::OSGB::CentralScale | ( |  | ) |
| inline static

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 206 of file OSGB.hpp.

## ◆ OriginLatitude()

Math::real GeographicLib::OSGB::OriginLatitude | ( |  | ) |
| inline static

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

Definition at line 214 of file OSGB.hpp.

## ◆ OriginLongitude()

Math::real GeographicLib::OSGB::OriginLongitude | ( |  | ) |
| inline static

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

Definition at line 220 of file OSGB.hpp.

Referenced by Forward(), and Reverse().

## ◆ FalseNorthing()

Math::real GeographicLib::OSGB::FalseNorthing | ( |  | ) |
| inline static

Returns
  false northing the OSGB projection (−100000 meters).

Definition at line 225 of file OSGB.hpp.

## ◆ FalseEasting()

Math::real GeographicLib::OSGB::FalseEasting | ( |  | ) |
| inline static

Returns
  false easting the OSGB projection (400000 meters).

Definition at line 230 of file OSGB.hpp.

Referenced by Forward(), and Reverse().

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

- OSGB.hpp
- OSGB.cpp