/** * \file CassiniSoldner.hpp * \brief Header for GeographicLib::CassiniSoldner class * * Copyright (c) Charles Karney (2009-2020) and licensed * under the MIT/X11 License. For more information, see * https://geographiclib.sourceforge.io/ **********************************************************************/ #if !defined(GEOGRAPHICLIB_CASSINISOLDNER_HPP) #define GEOGRAPHICLIB_CASSINISOLDNER_HPP 1 #include #include #include namespace GeographicLib { /** * \brief Cassini-Soldner projection * * Cassini-Soldner projection centered at an arbitrary position, \e lat0, \e * lon0, on the ellipsoid. This projection is a transverse cylindrical * equidistant projection. The projection from (\e lat, \e lon) to easting * and northing (\e x, \e y) is defined by geodesics as follows. Go north * along a geodesic a distance \e y from the central point; then turn * clockwise 90° and go a distance \e x along a geodesic. * (Although the initial heading is north, this changes to south if the pole * is crossed.) This procedure uniquely defines the reverse projection. The * forward projection is constructed as follows. Find the point (\e lat1, \e * lon1) on the meridian closest to (\e lat, \e lon). Here we consider the * full meridian so that \e lon1 may be either \e lon0 or \e lon0 + * 180°. \e x is the geodesic distance from (\e lat1, \e lon1) to * (\e lat, \e lon), appropriately signed according to which side of the * central meridian (\e lat, \e lon) lies. \e y is the shortest distance * along the meridian from (\e lat0, \e lon0) to (\e lat1, \e lon1), again, * appropriately signed according to the initial heading. [Note that, in the * case of prolate ellipsoids, the shortest meridional path from (\e lat0, \e * lon0) to (\e lat1, \e lon1) may not be the shortest path.] This procedure * uniquely defines the forward projection except for a small class of points * for which there may be two equally short routes for either leg of the * path. * * Because of the properties of geodesics, the (\e x, \e y) grid is * orthogonal. The scale in the easting direction is unity. The scale, \e * k, in the northing direction is unity on the central meridian and * increases away from the central meridian. The projection routines return * \e azi, the true bearing of the easting direction, and \e rk = 1/\e k, the * reciprocal of the scale in the northing direction. * * The conversions all take place using a Geodesic object (by default * Geodesic::WGS84()). For more information on geodesics see \ref geodesic. * The determination of (\e lat1, \e lon1) in the forward projection is by * solving the inverse geodesic problem for (\e lat, \e lon) and its twin * obtained by reflection in the meridional plane. The scale is found by * determining where two neighboring geodesics intersecting the central * meridian at \e lat1 and \e lat1 + \e dlat1 intersect and taking the ratio * of the reduced lengths for the two geodesics between that point and, * respectively, (\e lat1, \e lon1) and (\e lat, \e lon). * * Example of use: * \include example-CassiniSoldner.cpp * * GeodesicProj is a command-line utility * providing access to the functionality of AzimuthalEquidistant, Gnomonic, * and CassiniSoldner. **********************************************************************/ class GEOGRAPHICLIB_EXPORT CassiniSoldner { private: typedef Math::real real; Geodesic _earth; GeodesicLine _meridian; real _sbet0, _cbet0; static const unsigned maxit_ = 10; public: /** * Constructor for CassiniSoldner. * * @param[in] earth the Geodesic object to use for geodesic calculations. * By default this uses the WGS84 ellipsoid. * * This constructor makes an "uninitialized" object. Call Reset to set the * central latitude and longitude, prior to calling Forward and Reverse. **********************************************************************/ explicit CassiniSoldner(const Geodesic& earth = Geodesic::WGS84()); /** * Constructor for CassiniSoldner specifying a center point. * * @param[in] lat0 latitude of center point of projection (degrees). * @param[in] lon0 longitude of center point of projection (degrees). * @param[in] earth the Geodesic object to use for geodesic calculations. * By default this uses the WGS84 ellipsoid. * * \e lat0 should be in the range [−90°, 90°]. **********************************************************************/ CassiniSoldner(real lat0, real lon0, const Geodesic& earth = Geodesic::WGS84()); /** * Set the central point of the projection * * @param[in] lat0 latitude of center point of projection (degrees). * @param[in] lon0 longitude of center point of projection (degrees). * * \e lat0 should be in the range [−90°, 90°]. **********************************************************************/ void Reset(real lat0, real lon0); /** * Forward projection, from geographic to Cassini-Soldner. * * @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] azi azimuth of easting direction at point (degrees). * @param[out] rk reciprocal of azimuthal northing scale at point. * * \e lat should be in the range [−90°, 90°]. A call to * Forward followed by a call to Reverse will return the original (\e lat, * \e lon) (to within roundoff). The routine does nothing if the origin * has not been set. **********************************************************************/ void Forward(real lat, real lon, real& x, real& y, real& azi, real& rk) const; /** * Reverse projection, from Cassini-Soldner 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] azi azimuth of easting direction at point (degrees). * @param[out] rk reciprocal of azimuthal northing scale at point. * * A call to Reverse followed by a call to Forward will return the original * (\e x, \e y) (to within roundoff), provided that \e x and \e y are * sufficiently small not to "wrap around" the earth. The routine does * nothing if the origin has not been set. **********************************************************************/ void Reverse(real x, real y, real& lat, real& lon, real& azi, real& rk) const; /** * CassiniSoldner::Forward without returning the azimuth and scale. **********************************************************************/ void Forward(real lat, real lon, real& x, real& y) const { real azi, rk; Forward(lat, lon, x, y, azi, rk); } /** * CassiniSoldner::Reverse without returning the azimuth and scale. **********************************************************************/ void Reverse(real x, real y, real& lat, real& lon) const { real azi, rk; Reverse(x, y, lat, lon, azi, rk); } /** \name Inspector functions **********************************************************************/ ///@{ /** * @return true if the object has been initialized. **********************************************************************/ bool Init() const { return _meridian.Init(); } /** * @return \e lat0 the latitude of origin (degrees). **********************************************************************/ Math::real LatitudeOrigin() const { return _meridian.Latitude(); } /** * @return \e lon0 the longitude of origin (degrees). **********************************************************************/ Math::real LongitudeOrigin() const { return _meridian.Longitude(); } /** * @return \e a the equatorial radius of the ellipsoid (meters). This is * the value inherited from the Geodesic object used in the constructor. **********************************************************************/ Math::real EquatorialRadius() const { return _earth.EquatorialRadius(); } /** * @return \e f the flattening of the ellipsoid. This is the value * inherited from the Geodesic object used in the constructor. **********************************************************************/ Math::real Flattening() const { return _earth.Flattening(); } /** * \deprecated An old name for EquatorialRadius(). **********************************************************************/ GEOGRAPHICLIB_DEPRECATED("Use EquatorialRadius()") Math::real MajorRadius() const { return EquatorialRadius(); } ///@} }; } // namespace GeographicLib #endif // GEOGRAPHICLIB_CASSINISOLDNER_HPP