/** * \file OSGB.hpp * \brief Header for GeographicLib::OSGB class * * Copyright (c) Charles Karney (2010-2020) and licensed * under the MIT/X11 License. For more information, see * https://geographiclib.sourceforge.io/ **********************************************************************/ #if !defined(GEOGRAPHICLIB_OSGB_HPP) #define GEOGRAPHICLIB_OSGB_HPP 1 #include #include #if defined(_MSC_VER) // Squelch warnings about dll vs string # pragma warning (push) # pragma warning (disable: 4251) #endif namespace GeographicLib { /** * \brief 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 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: * \include example-OSGB.cpp **********************************************************************/ class GEOGRAPHICLIB_EXPORT OSGB { private: typedef Math::real real; static const char* const letters_; static const char* const digits_; static const TransverseMercator& OSGBTM(); enum { base_ = 10, tile_ = 100000, tilelevel_ = 5, tilegrid_ = 5, tileoffx_ = 2 * tilegrid_, tileoffy_ = 1 * tilegrid_, minx_ = - tileoffx_ * tile_, miny_ = - tileoffy_ * tile_, maxx_ = (tilegrid_*tilegrid_ - tileoffx_) * tile_, maxy_ = (tilegrid_*tilegrid_ - tileoffy_) * tile_, // Maximum precision is um maxprec_ = 5 + 6, }; static real computenorthoffset(); static void CheckCoords(real x, real y); OSGB(); // Disable constructor public: /** * Forward projection, from geographic to OSGB coordinates. * * @param[in] lat latitude of point (degrees). * @param[in] lon longitude of point (degrees). * @param[out] x easting of point (meters). * @param[out] y northing of point (meters). * @param[out] gamma meridian convergence at point (degrees). * @param[out] k scale of projection at point. * * \e lat should be in the range [−90°, 90°]. **********************************************************************/ static void Forward(real lat, real lon, real& x, real& y, real& gamma, real& k) { OSGBTM().Forward(OriginLongitude(), lat, lon, x, y, gamma, k); x += FalseEasting(); y += computenorthoffset(); } /** * Reverse projection, from OSGB coordinates to geographic. * * @param[in] x easting of point (meters). * @param[in] y northing of point (meters). * @param[out] lat latitude of point (degrees). * @param[out] lon longitude of point (degrees). * @param[out] gamma meridian convergence at point (degrees). * @param[out] k scale of projection at point. * * The value of \e lon returned is in the range [−180°, * 180°]. **********************************************************************/ static void Reverse(real x, real y, real& lat, real& lon, real& gamma, real& k) { x -= FalseEasting(); y -= computenorthoffset(); OSGBTM().Reverse(OriginLongitude(), x, y, lat, lon, gamma, k); } /** * OSGB::Forward without returning the convergence and scale. **********************************************************************/ static void Forward(real lat, real lon, real& x, real& y) { real gamma, k; Forward(lat, lon, x, y, gamma, k); } /** * OSGB::Reverse without returning the convergence and scale. **********************************************************************/ static void Reverse(real x, real y, real& lat, real& lon) { real gamma, k; Reverse(x, y, lat, lon, gamma, k); } /** * Convert OSGB coordinates to a grid reference. * * @param[in] x easting of point (meters). * @param[in] y northing of point (meters). * @param[in] prec precision relative to 100 km. * @param[out] gridref National Grid reference. * @exception GeographicErr if \e prec, \e x, or \e y is outside its * allowed range. * @exception std::bad_alloc if the memory for \e gridref can't be * allocatied. * * \e 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 \e x or \e y is NaN, the returned grid reference is "INVALID". **********************************************************************/ static void GridReference(real x, real y, int prec, std::string& gridref); /** * Convert OSGB coordinates to a grid reference. * * @param[in] gridref National Grid reference. * @param[out] x easting of point (meters). * @param[out] y northing of point (meters). * @param[out] prec precision relative to 100 km. * @param[in] centerp if true (default), return center of the grid square, * else return SW (lower left) corner. * @exception GeographicErr if \e 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 \e gridref are "IN", then \e x and \e y are * set to NaN and \e prec is set to −2. **********************************************************************/ static void GridReference(const std::string& gridref, real& x, real& y, int& prec, bool centerp = true); /** \name Inspector functions **********************************************************************/ ///@{ /** * @return \e 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 (p. 37) of A guide to coordinate systems * in Great Britain, v2.2 (Dec. 2013). **********************************************************************/ static Math::real EquatorialRadius() { // result is about 6377563.3960320664406 m using std::pow; return pow(real(10), real(48401603 - 100000000) / 100000000) * real(20923713); } /** * @return \e f the inverse flattening of the Airy 1830 ellipsoid. * * For the Airy 1830 ellipsoid, \e a = 20923713 ft and \e 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.) **********************************************************************/ static Math::real Flattening() { return real(20923713 - 20853810) / real(20923713); } /** * @return \e 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. **********************************************************************/ static Math::real CentralScale() { using std::pow; return pow(real(10), real(9998268 - 10000000) / 10000000); } /** * @return latitude of the origin for the OSGB projection (49 degrees). **********************************************************************/ static Math::real OriginLatitude() { return real(49); } /** * @return longitude of the origin for the OSGB projection (−2 * degrees). **********************************************************************/ static Math::real OriginLongitude() { return real(-2); } /** * @return false northing the OSGB projection (−100000 meters). **********************************************************************/ static Math::real FalseNorthing() { return real(-100000); } /** * @return false easting the OSGB projection (400000 meters). **********************************************************************/ static Math::real FalseEasting() { return real(400000); } /** * \deprecated An old name for EquatorialRadius(). **********************************************************************/ GEOGRAPHICLIB_DEPRECATED("Use EquatorialRadius()") static Math::real MajorRadius() { return EquatorialRadius(); } ///@} }; } // namespace GeographicLib #if defined(_MSC_VER) # pragma warning (pop) #endif #endif // GEOGRAPHICLIB_OSGB_HPP