GeographicLib 2.5
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Ordnance Survey grid system for Great Britain. More...
#include <GeographicLib/OSGB.hpp>
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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 () |
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
Example of use:
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Forward projection, from geographic to OSGB coordinates.
[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().
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Reverse projection, from OSGB coordinates to geographic.
[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().
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OSGB::Forward without returning the convergence and scale.
Definition at line 104 of file OSGB.hpp.
References Forward().
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OSGB::Reverse without returning the convergence and scale.
Definition at line 112 of file OSGB.hpp.
References Reverse().
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Convert OSGB coordinates to a grid reference.
[in] | x | easting of point (meters). |
[in] | y | northing of point (meters). |
[in] | prec | precision relative to 100 km. |
[out] | gridref | National Grid reference. |
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:
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().
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Convert OSGB grid reference to coordinates.
[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. |
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 88 of file OSGB.cpp.
References GeographicLib::Utility::lookup(), and GeographicLib::Math::NaN().
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inlinestatic |
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).
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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.)
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