Cassini-Soldner Projection. More...
#include <GeographicLib/CassiniSoldner.hpp>
Public Member Functions | |
CassiniSoldner (const Geodesic &earth=Geodesic::WGS84) throw () | |
CassiniSoldner (real lat0, real lon0, const Geodesic &earth=Geodesic::WGS84) throw () | |
void | Reset (real lat0, real lon0) throw () |
void | Forward (real lat, real lon, real &x, real &y, real &azi, real &rk) const throw () |
void | Reverse (real x, real y, real &lat, real &lon, real &azi, real &rk) const throw () |
void | Forward (real lat, real lon, real &x, real &y) const throw () |
void | Reverse (real x, real y, real &lat, real &lon) const throw () |
Inspector functions | |
bool | Init () const throw () |
Math::real | LatitudeOrigin () const throw () |
Math::real | LongitudeOrigin () const throw () |
Math::real | MajorRadius () const throw () |
Math::real | InverseFlattening () const throw () |
Cassini-Soldner Projection.
Cassini-Soldner projection centered at an arbitrary position, lat0, lon0, on the ellipsoid. This projection is a transverse cylindrical equidistant projection. The projection from (lat, lon) to easting and northing (x, y) is defined by geodesics as follows. Go north along a geodesic a distance y from the central point; then turn clockwise 90o and go a distance 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 (lat1, lon1) on the meridian closest to (lat, lon). Here we consider the full meridian so that lon1 may be either lon0 or lon0 + 180o. x is the geodesic distance from (lat1, lon1) to (lat, lon), appropriately signed according to which side of the central meridian (lat, lon) lies. y is the shortest distance along the meridian from (lat0, lon0) to (lat1, lon1), again, appropriately signed according to the initial heading. [Note that, in the case of prolate ellipsoids, the shortest meridional path from (lat0, lon0) to (lat1, 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 (x, y) grid is orthogonal. The scale in the easting direction is unity. The scale, k, in the northing direction is unity on the central meridian and increases away from the central meridian. The projection routines return azi, the true bearing of the easting direction, and rk = 1/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 Geodesics on the Ellipsoid. The determination of (lat1, lon1) in the forward projection is by solving the inverse geodesic problem for (lat, lon) and its twin obtained by reflection in the meridional plane. The scale is found by determining where two neighboring geodesics intersecting the central meridan at lat1 and lat1 + dlat1 intersect and taking the ratio of the reduced lengths for the two geodesics between that point and, respectively, (lat1, lon1) and (lat, lon).
Definition at line 62 of file CassiniSoldner.hpp.
GeographicLib::CassiniSoldner::CassiniSoldner | ( | const Geodesic & | earth = Geodesic::WGS84 |
) | throw () [inline, explicit] |
Constructor for CassiniSoldner.
[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 longuitude, prior to calling Forward and Reverse.
Definition at line 105 of file CassiniSoldner.hpp.
GeographicLib::CassiniSoldner::CassiniSoldner | ( | real | lat0, | |
real | lon0, | |||
const Geodesic & | earth = Geodesic::WGS84 | |||
) | throw () [inline] |
Constructor for CassiniSoldner specifying a center point.
[in] | lat0 | latitude of center point of projection (degrees). |
[in] | lon0 | longitude of center point of projection (degrees). |
[in] | earth | the Geodesic object to use for geodesic calculations. By default this uses the WGS84 ellipsoid. |
lat0 should be in the range [-90, 90] and lon0 should be in the range [-180, 360].
Definition at line 119 of file CassiniSoldner.hpp.
References Reset().
void GeographicLib::CassiniSoldner::Reset | ( | real | lat0, | |
real | lon0 | |||
) | throw () |
Set the central point of the projection
[in] | lat0 | latitude of center point of projection (degrees). |
[in] | lon0 | longitude of center point of projection (degrees). |
lat0 should be in the range [-90, 90] and lon0 should be in the range [-180, 360].
Definition at line 26 of file CassiniSoldner.cpp.
Referenced by CassiniSoldner().
void GeographicLib::CassiniSoldner::Forward | ( | real | lat, | |
real | lon, | |||
real & | x, | |||
real & | y, | |||
real & | azi, | |||
real & | rk | |||
) | const throw () |
Forward projection, from geographic to Cassini-Soldner.
[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] | azi | azimuth of easting direction at point (degrees). |
[out] | rk | reciprocal of azimuthal northing scale at point. |
lat should be in the range [-90, 90] and lon should be in the range [-180, 360]. A call to Forward followed by a call to Reverse will return the original (lat, lon) (to within roundoff). The routine does nothing if the origin has not been set.
Definition at line 39 of file CassiniSoldner.cpp.
Referenced by Forward().
void GeographicLib::CassiniSoldner::Reverse | ( | real | x, | |
real | y, | |||
real & | lat, | |||
real & | lon, | |||
real & | azi, | |||
real & | rk | |||
) | const throw () |
Reverse projection, from Cassini-Soldner 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] | azi | azimuth of easting direction at point (degrees). |
[out] | rk | reciprocal of azimuthal northing scale at point. |
A call to Reverse followed by a call to Forward will return the original (x, y) (to within roundoff), provided that x and y are sufficiently small not to "wrap around" the earth. The routine does nothing if the origin has not been set.
Definition at line 87 of file CassiniSoldner.cpp.
Referenced by Reverse().
void GeographicLib::CassiniSoldner::Forward | ( | real | lat, | |
real | lon, | |||
real & | x, | |||
real & | y | |||
) | const throw () [inline] |
CassiniSoldner::Forward without returning the azimuth and scale.
Definition at line 175 of file CassiniSoldner.hpp.
References Forward().
void GeographicLib::CassiniSoldner::Reverse | ( | real | x, | |
real | y, | |||
real & | lat, | |||
real & | lon | |||
) | const throw () [inline] |
CassiniSoldner::Reverse without returning the azimuth and scale.
Definition at line 184 of file CassiniSoldner.hpp.
References Reverse().
bool GeographicLib::CassiniSoldner::Init | ( | ) | const throw () [inline] |
Definition at line 196 of file CassiniSoldner.hpp.
References GeographicLib::GeodesicLine::Init().
Math::real GeographicLib::CassiniSoldner::LatitudeOrigin | ( | ) | const throw () [inline] |
Definition at line 201 of file CassiniSoldner.hpp.
References GeographicLib::GeodesicLine::Latitude().
Math::real GeographicLib::CassiniSoldner::LongitudeOrigin | ( | ) | const throw () [inline] |
Definition at line 207 of file CassiniSoldner.hpp.
References GeographicLib::GeodesicLine::Longitude().
Math::real GeographicLib::CassiniSoldner::MajorRadius | ( | ) | const throw () [inline] |
Definition at line 214 of file CassiniSoldner.hpp.
References GeographicLib::Geodesic::MajorRadius().
Math::real GeographicLib::CassiniSoldner::InverseFlattening | ( | ) | const throw () [inline] |
Definition at line 221 of file CassiniSoldner.hpp.
References GeographicLib::Geodesic::InverseFlattening().