GeographicLib: OSGB.hpp Source File

GeographicLib 2.5

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OSGB.hpp
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1/**
2 * \file OSGB.hpp
3 * \brief Header for GeographicLib::OSGB class
4 *
5 * Copyright (c) Charles Karney (2010-2024) <karney@alum.mit.edu> and licensed
6 * under the MIT/X11 License. For more information, see
7 * https://geographiclib.sourceforge.io/
8 **********************************************************************/
9
10#if !defined(GEOGRAPHICLIB_OSGB_HPP)
11#define GEOGRAPHICLIB_OSGB_HPP 1
12
13#include <GeographicLib/Constants.hpp>
14#include <GeographicLib/TransverseMercator.hpp>
15
16namespace GeographicLib {
17
18 /**
19 * \brief Ordnance Survey grid system for Great Britain
20 *
21 * The class implements the coordinate system used by the Ordnance Survey for
22 * maps of Great Britain and conversions to the grid reference system.
23 *
24 * See
25 * - <a href="https://www.ordnancesurvey.co.uk/documents/resources/guide-coordinate-systems-great-britain.pdf">
26 * A guide to coordinate systems in Great Britain</a>
27 * - <a href="https://www.ordnancesurvey.co.uk/documents/resources/guide-to-nationalgrid.pdf">
28 * Using the National Grid</a>
29 *
30 * \warning the latitudes and longitudes for the Ordnance Survey grid
31 * system do not use the WGS84 datum. Do not use the values returned by this
32 * class in the UTMUPS, MGRS, or Geoid classes without first converting the
33 * datum (and vice versa).
34 *
35 * Example of use:
36 * \include example-OSGB.cpp
37 **********************************************************************/
38 class GEOGRAPHICLIB_EXPORT OSGB {
39 private:
40 typedef Math::real real;
41 static const char* const letters_;
42 static const char* const digits_;
43 static const TransverseMercator& OSGBTM();
44 static constexpr int base_ = 10;
45 static constexpr int tile_ = 100000;
46 static constexpr int tilelevel_ = 5;
47 static constexpr int tilegrid_ = 5;
48 static constexpr int tileoffx_ = 2 * tilegrid_;
49 static constexpr int tileoffy_ = 1 * tilegrid_;
50 static constexpr int minx_ = - tileoffx_ * tile_;
51 static constexpr int miny_ = - tileoffy_ * tile_;
52 static constexpr int maxx_ = (tilegrid_*tilegrid_ - tileoffx_) * tile_;
53 static constexpr int maxy_ = (tilegrid_*tilegrid_ - tileoffy_) * tile_;
54 // Maximum precision is um
55 static constexpr int maxprec_ = 5 + 6;
56 static real computenorthoffset();
57 static void CheckCoords(real x, real y);
58 OSGB() = delete; // Disable constructor
59 public:
60
61 /**
62 * Forward projection, from geographic to OSGB coordinates.
63 *
64 * @param[in] lat latitude of point (degrees).
65 * @param[in] lon longitude of point (degrees).
66 * @param[out] x easting of point (meters).
67 * @param[out] y northing of point (meters).
68 * @param[out] gamma meridian convergence at point (degrees).
69 * @param[out] k scale of projection at point.
70 *
71 * \e lat should be in the range [&minus;90&deg;, 90&deg;].
72 **********************************************************************/
73 static void Forward(real lat, real lon,
74 real& x, real& y, real& gamma, real& k) {
75 OSGBTM().Forward(OriginLongitude(), lat, lon, x, y, gamma, k);
76 x += FalseEasting();
77 y += computenorthoffset();
78 }
79
80 /**
81 * Reverse projection, from OSGB coordinates to geographic.
82 *
83 * @param[in] x easting of point (meters).
84 * @param[in] y northing of point (meters).
85 * @param[out] lat latitude of point (degrees).
86 * @param[out] lon longitude of point (degrees).
87 * @param[out] gamma meridian convergence at point (degrees).
88 * @param[out] k scale of projection at point.
89 *
90 * The value of \e lon returned is in the range [&minus;180&deg;,
91 * 180&deg;].
92 **********************************************************************/
93
94 static void Reverse(real x, real y,
95 real& lat, real& lon, real& gamma, real& k) {
96 x -= FalseEasting();
97 y -= computenorthoffset();
98 OSGBTM().Reverse(OriginLongitude(), x, y, lat, lon, gamma, k);
99 }
100
101 /**
102 * OSGB::Forward without returning the convergence and scale.
103 **********************************************************************/
104 static void Forward(real lat, real lon, real& x, real& y) {
105 real gamma, k;
106 Forward(lat, lon, x, y, gamma, k);
107 }
108
109 /**
110 * OSGB::Reverse without returning the convergence and scale.
111 **********************************************************************/
112 static void Reverse(real x, real y, real& lat, real& lon) {
113 real gamma, k;
114 Reverse(x, y, lat, lon, gamma, k);
115 }
116
117 /**
118 * Convert OSGB coordinates to a grid reference.
119 *
120 * @param[in] x easting of point (meters).
121 * @param[in] y northing of point (meters).
122 * @param[in] prec precision relative to 100 km.
123 * @param[out] gridref National Grid reference.
124 * @exception GeographicErr if \e prec, \e x, or \e y is outside its
125 * allowed range.
126 * @exception std::bad_alloc if the memory for \e gridref can't be
127 * allocatied.
128 *
129 * \e prec specifies the precision of the grid reference string as follows:
130 * - prec = 0 (min), 100km
131 * - prec = 1, 10km
132 * - prec = 2, 1km
133 * - prec = 3, 100m
134 * - prec = 4, 10m
135 * - prec = 5, 1m
136 * - prec = 6, 0.1m
137 * - prec = 11 (max), 1&mu;m
138 *
139 * The easting must be in the range [&minus;1000 km, 1500 km) and the
140 * northing must be in the range [&minus;500 km, 2000 km). These bounds
141 * are consistent with rules for the letter designations for the grid
142 * system.
143 *
144 * If \e x or \e y is NaN, the returned grid reference is "INVALID".
145 **********************************************************************/
146 static void GridReference(real x, real y, int prec, std::string& gridref);
147
148 /**
149 * Convert OSGB grid reference to coordinates.
150 *
151 * @param[in] gridref National Grid reference.
152 * @param[out] x easting of point (meters).
153 * @param[out] y northing of point (meters).
154 * @param[out] prec precision relative to 100 km.
155 * @param[in] centerp if true (default), return center of the grid square,
156 * else return SW (lower left) corner.
157 * @exception GeographicErr if \e gridref is illegal.
158 *
159 * The grid reference must be of the form: two letters (not including I)
160 * followed by an even number of digits (up to 22).
161 *
162 * If the first 2 characters of \e gridref are "IN", then \e x and \e y are
163 * set to NaN and \e prec is set to &minus;2.
164 **********************************************************************/
165 static void GridReference(const std::string& gridref,
166 real& x, real& y, int& prec,
167 bool centerp = true);
168
169 /** \name Inspector functions
170 **********************************************************************/
171 ///@{
172 /**
173 * @return \e a the equatorial radius of the Airy 1830 ellipsoid (meters).
174 *
175 * This is 20923713 ft converted to meters using the rule 1 ft =
176 * 10<sup>9.48401603&minus;10</sup> m. The Airy 1830 value is returned
177 * because the OSGB projection is based on this ellipsoid. The conversion
178 * factor from feet to meters is the one used for the 1936 retriangulation
179 * of Britain; see Section A.1 (footnote 10 on p. 44) of <i>A guide to
180 * coordinate systems in Great Britain</i>, v3.6 (2020).
181 **********************************************************************/
182 static Math::real EquatorialRadius() {
183 // result is about 6377563.3960320664406 m
184 using std::pow;
185 return pow(real(10), real(48401603 - 100000000) / 100000000)
186 * real(20923713);
187 }
188
189 /**
190 * @return \e f the inverse flattening of the Airy 1830 ellipsoid.
191 *
192 * For the Airy 1830 ellipsoid, \e a = 20923713 ft and \e b = 20853810 ft;
193 * thus the flattening = (20923713 &minus; 20853810)/20923713 =
194 * 7767/2324857 = 1/299.32496459... (The Airy 1830 value is returned
195 * because the OSGB projection is based on this ellipsoid.)
196 **********************************************************************/
197 static Math::real Flattening()
198 { return real(20923713 - 20853810) / real(20923713); }
199
200 /**
201 * @return \e k0 central scale for the OSGB projection (0.9996012717...).
202 *
203 * C. J. Mugnier, Grids &amp; Datums, PE&amp;RS, Oct. 2003, states that
204 * this is defined as 10<sup>9.9998268&minus;10</sup>.
205 **********************************************************************/
206 static Math::real CentralScale() {
207 using std::pow;
208 return pow(real(10), real(9998268 - 10000000) / 10000000);
209 }
210
211 /**
212 * @return latitude of the origin for the OSGB projection (49 degrees).
213 **********************************************************************/
214 static Math::real OriginLatitude() { return real(49); }
215
216 /**
217 * @return longitude of the origin for the OSGB projection (&minus;2
218 * degrees).
219 **********************************************************************/
220 static Math::real OriginLongitude() { return real(-2); }
221
222 /**
223 * @return false northing the OSGB projection (&minus;100000 meters).
224 **********************************************************************/
225 static Math::real FalseNorthing() { return real(-100000); }
226
227 /**
228 * @return false easting the OSGB projection (400000 meters).
229 **********************************************************************/
230 static Math::real FalseEasting() { return real(400000); }
231 ///@}
232
233 };
234
235} // namespace GeographicLib
236
237#endif // GEOGRAPHICLIB_OSGB_HPP
Constants.hpp
Header for GeographicLib::Constants class.
GEOGRAPHICLIB_EXPORT
#define GEOGRAPHICLIB_EXPORT
Definition Constants.hpp:67
real
GeographicLib::Math::real real
Definition GeodSolve.cpp:28
TransverseMercator.hpp
Header for GeographicLib::TransverseMercator class.
GeographicLib::Math::real
double real
Definition Math.hpp:110
GeographicLib::OSGB::Forward
static void Forward(real lat, real lon, real &x, real &y)
Definition OSGB.hpp:104
GeographicLib::OSGB::OriginLongitude
static Math::real OriginLongitude()
Definition OSGB.hpp:220
GeographicLib::OSGB::CentralScale
static Math::real CentralScale()
Definition OSGB.hpp:206
GeographicLib::OSGB::EquatorialRadius
static Math::real EquatorialRadius()
Definition OSGB.hpp:182
GeographicLib::OSGB::FalseNorthing
static Math::real FalseNorthing()
Definition OSGB.hpp:225
GeographicLib::OSGB::Forward
static void Forward(real lat, real lon, real &x, real &y, real &gamma, real &k)
Definition OSGB.hpp:73
GeographicLib::OSGB::Flattening
static Math::real Flattening()
Definition OSGB.hpp:197
GeographicLib::OSGB::FalseEasting
static Math::real FalseEasting()
Definition OSGB.hpp:230
GeographicLib::OSGB::Reverse
static void Reverse(real x, real y, real &lat, real &lon)
Definition OSGB.hpp:112
GeographicLib::OSGB::OriginLatitude
static Math::real OriginLatitude()
Definition OSGB.hpp:214
GeographicLib::OSGB::Reverse
static void Reverse(real x, real y, real &lat, real &lon, real &gamma, real &k)
Definition OSGB.hpp:94
GeographicLib::TransverseMercator
Transverse Mercator projection.
Definition TransverseMercator.hpp:94
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12