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Geoid.hpp
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/**
* \file Geoid.hpp
* \brief Header for GeographicLib::Geoid class
*
* Copyright (c) Charles Karney (2009-2022) <karney@alum.mit.edu> and licensed
* under the MIT/X11 License. For more information, see
* https://geographiclib.sourceforge.io/
**********************************************************************/
#if !defined(GEOGRAPHICLIB_GEOID_HPP)
#define GEOGRAPHICLIB_GEOID_HPP 1
#include <vector>
#include <fstream>
#include <GeographicLib/Constants.hpp>
#if defined(_MSC_VER)
// Squelch warnings about dll vs vector and constant conditional expressions
# pragma warning (push)
# pragma warning (disable: 4251 4127)
#endif
#if !defined(GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH)
/**
* The size of the pixel data in the pgm data files for the geoids. 2 is the
* standard size corresponding to a maxval 2<sup>16</sup>&minus;1. Setting it
* to 4 uses a maxval of 2<sup>32</sup>&minus;1 and changes the extension for
* the data files from .pgm to .pgm4. Note that the format of these pgm4 files
* is a non-standard extension of the pgm format.
**********************************************************************/
# define GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH 2
#endif
namespace GeographicLib {
/**
* \brief Looking up the height of the geoid above the ellipsoid
*
* This class evaluates the height of one of the standard geoids, EGM84,
* EGM96, or EGM2008 by bilinear or cubic interpolation into a rectangular
* grid of data. These geoid models are documented in
* - EGM84:
* https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84#tab_egm84
* - EGM96:
* https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84#tab_egm96
* - EGM2008:
* https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84#tab_egm2008
*
* The geoids are defined in terms of spherical harmonics. However in order
* to provide a quick and flexible method of evaluating the geoid heights,
* this class evaluates the height by interpolation into a grid of
* precomputed values.
*
* The height of the geoid above the ellipsoid, \e N, is sometimes called the
* geoid undulation. It can be used to convert a height above the ellipsoid,
* \e h, to the corresponding height above the geoid (the orthometric height,
* roughly the height above mean sea level), \e H, using the relations
*
* &nbsp;&nbsp;&nbsp;\e h = \e N + \e H;
* &nbsp;&nbsp;\e H = &minus;\e N + \e h.
*
* See \ref geoid for details of how to install the data sets, the data
* format, estimates of the interpolation errors, and how to use caching.
*
* This class is typically \e not thread safe in that a single instantiation
* cannot be safely used by multiple threads because of the way the object
* reads the data set and because it maintains a single-cell cache. If
* multiple threads need to calculate geoid heights they should all construct
* thread-local instantiations. Alternatively, set the optional \e
* threadsafe parameter to true in the constructor. This causes the
* constructor to read all the data into memory and to turn off the
* single-cell caching which results in a Geoid object which \e is thread
* safe.
*
* Example of use:
* \include example-Geoid.cpp
*
* <a href="GeoidEval.1.html">GeoidEval</a> is a command-line utility
* providing access to the functionality of Geoid.
**********************************************************************/
class GEOGRAPHICLIB_EXPORT Geoid {
private:
typedef Math::real real;
#if GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH != 4
typedef unsigned short pixel_t;
static const unsigned pixel_size_ = 2;
static const unsigned pixel_max_ = 0xffffu;
#else
typedef unsigned pixel_t;
static const unsigned pixel_size_ = 4;
static const unsigned pixel_max_ = 0xffffffffu;
#endif
static const unsigned stencilsize_ = 12;
static const unsigned nterms_ = ((3 + 1) * (3 + 2))/2; // for a cubic fit
static const int c0_;
static const int c0n_;
static const int c0s_;
static const int c3_[stencilsize_ * nterms_];
static const int c3n_[stencilsize_ * nterms_];
static const int c3s_[stencilsize_ * nterms_];
std::string _name, _dir, _filename;
const bool _cubic;
const real _a, _e2, _degree, _eps;
mutable std::ifstream _file;
real _rlonres, _rlatres;
std::string _description, _datetime;
real _offset, _scale, _maxerror, _rmserror;
int _width, _height;
unsigned long long _datastart, _swidth;
bool _threadsafe;
// Area cache
mutable std::vector< std::vector<pixel_t> > _data;
mutable bool _cache;
// NE corner and extent of cache
mutable int _xoffset, _yoffset, _xsize, _ysize;
// Cell cache
mutable int _ix, _iy;
mutable real _v00, _v01, _v10, _v11;
mutable real _t[nterms_];
void filepos(int ix, int iy) const {
_file.seekg(std::streamoff
(_datastart +
pixel_size_ * (unsigned(iy)*_swidth + unsigned(ix))));
}
real rawval(int ix, int iy) const {
if (ix < 0)
ix += _width;
else if (ix >= _width)
ix -= _width;
if (_cache && iy >= _yoffset && iy < _yoffset + _ysize &&
((ix >= _xoffset && ix < _xoffset + _xsize) ||
(ix + _width >= _xoffset && ix + _width < _xoffset + _xsize))) {
return real(_data[iy - _yoffset]
[ix >= _xoffset ? ix - _xoffset : ix + _width - _xoffset]);
} else {
if (iy < 0 || iy >= _height) {
iy = iy < 0 ? -iy : 2 * (_height - 1) - iy;
ix += (ix < _width/2 ? 1 : -1) * _width/2;
}
try {
filepos(ix, iy);
// initial values to suppress warnings in case get fails
char a = 0, b = 0;
_file.get(a);
_file.get(b);
unsigned r = ((unsigned char)(a) << 8) | (unsigned char)(b);
// for C++17 use if constexpr
if (pixel_size_ == 4) {
_file.get(a);
_file.get(b);
r = (r << 16) | ((unsigned char)(a) << 8) | (unsigned char)(b);
}
return real(r);
}
catch (const std::exception& e) {
// throw GeographicErr("Error reading " + _filename + ": "
// + e.what());
// triggers complaints about the "binary '+'" under Visual Studio.
// So use '+=' instead.
std::string err("Error reading ");
err += _filename;
err += ": ";
err += e.what();
throw GeographicErr(err);
}
}
}
real height(real lat, real lon) const;
Geoid(const Geoid&) = delete; // copy constructor not allowed
Geoid& operator=(const Geoid&) = delete; // copy assignment not allowed
public:
/**
* Flags indicating conversions between heights above the geoid and heights
* above the ellipsoid.
**********************************************************************/
enum convertflag {
/**
* The multiplier for converting from heights above the ellipsoid to
* heights above the geoid.
**********************************************************************/
ELLIPSOIDTOGEOID = -1,
/**
* No conversion.
**********************************************************************/
NONE = 0,
/**
* The multiplier for converting from heights above the geoid to heights
* above the ellipsoid.
**********************************************************************/
GEOIDTOELLIPSOID = 1,
};
/** \name Setting up the geoid
**********************************************************************/
///@{
/**
* Construct a geoid.
*
* @param[in] name the name of the geoid.
* @param[in] path (optional) directory for data file.
* @param[in] cubic (optional) interpolation method; false means bilinear,
* true (the default) means cubic.
* @param[in] threadsafe (optional), if true, construct a thread safe
* object. The default is false
* @exception GeographicErr if the data file cannot be found, is
* unreadable, or is corrupt.
* @exception GeographicErr if \e threadsafe is true but the memory
* necessary for caching the data can't be allocated.
*
* The data file is formed by appending ".pgm" to the name. If \e path is
* specified (and is non-empty), then the file is loaded from directory, \e
* path. Otherwise the path is given by DefaultGeoidPath(). If the \e
* threadsafe parameter is true, the data set is read into memory, the data
* file is closed, and single-cell caching is turned off; this results in a
* Geoid object which \e is thread safe.
**********************************************************************/
explicit Geoid(const std::string& name, const std::string& path = "",
bool cubic = true, bool threadsafe = false);
/**
* Set up a cache.
*
* @param[in] south latitude (degrees) of the south edge of the cached
* area.
* @param[in] west longitude (degrees) of the west edge of the cached area.
* @param[in] north latitude (degrees) of the north edge of the cached
* area.
* @param[in] east longitude (degrees) of the east edge of the cached area.
* @exception GeographicErr if the memory necessary for caching the data
* can't be allocated (in this case, you will have no cache and can try
* again with a smaller area).
* @exception GeographicErr if there's a problem reading the data.
* @exception GeographicErr if this is called on a threadsafe Geoid.
*
* Cache the data for the specified "rectangular" area bounded by the
* parallels \e south and \e north and the meridians \e west and \e east.
* \e east is always interpreted as being east of \e west, if necessary by
* adding 360&deg; to its value. \e south and \e north should be in
* the range [&minus;90&deg;, 90&deg;].
**********************************************************************/
void CacheArea(real south, real west, real north, real east) const;
/**
* Cache all the data.
*
* @exception GeographicErr if the memory necessary for caching the data
* can't be allocated (in this case, you will have no cache and can try
* again with a smaller area).
* @exception GeographicErr if there's a problem reading the data.
* @exception GeographicErr if this is called on a threadsafe Geoid.
*
* On most computers, this is fast for data sets with grid resolution of 5'
* or coarser. For a 1' grid, the required RAM is 450MB; a 2.5' grid needs
* 72MB; and a 5' grid needs 18MB.
**********************************************************************/
void CacheAll() const { CacheArea(real(-Math::qd), real(0),
real( Math::qd), real(Math::td)); }
/**
* Clear the cache. This never throws an error. (This does nothing with a
* thread safe Geoid.)
**********************************************************************/
void CacheClear() const;
///@}
/** \name Compute geoid heights
**********************************************************************/
///@{
/**
* Compute the geoid height at a point
*
* @param[in] lat latitude of the point (degrees).
* @param[in] lon longitude of the point (degrees).
* @exception GeographicErr if there's a problem reading the data; this
* never happens if (\e lat, \e lon) is within a successfully cached
* area.
* @return the height of the geoid above the ellipsoid (meters).
*
* The latitude should be in [&minus;90&deg;, 90&deg;].
**********************************************************************/
Math::real operator()(real lat, real lon) const {
return height(lat, lon);
}
/**
* Convert a height above the geoid to a height above the ellipsoid and
* vice versa.
*
* @param[in] lat latitude of the point (degrees).
* @param[in] lon longitude of the point (degrees).
* @param[in] h height of the point (degrees).
* @param[in] d a Geoid::convertflag specifying the direction of the
* conversion; Geoid::GEOIDTOELLIPSOID means convert a height above the
* geoid to a height above the ellipsoid; Geoid::ELLIPSOIDTOGEOID means
* convert a height above the ellipsoid to a height above the geoid.
* @exception GeographicErr if there's a problem reading the data; this
* never happens if (\e lat, \e lon) is within a successfully cached
* area.
* @return converted height (meters).
**********************************************************************/
Math::real ConvertHeight(real lat, real lon, real h,
convertflag d) const {
return h + real(d) * height(lat, lon);
}
///@}
/** \name Inspector functions
**********************************************************************/
///@{
/**
* @return geoid description, if available, in the data file; if
* absent, return "NONE".
**********************************************************************/
const std::string& Description() const { return _description; }
/**
* @return date of the data file; if absent, return "UNKNOWN".
**********************************************************************/
const std::string& DateTime() const { return _datetime; }
/**
* @return full file name used to load the geoid data.
**********************************************************************/
const std::string& GeoidFile() const { return _filename; }
/**
* @return "name" used to load the geoid data (from the first argument of
* the constructor).
**********************************************************************/
const std::string& GeoidName() const { return _name; }
/**
* @return directory used to load the geoid data.
**********************************************************************/
const std::string& GeoidDirectory() const { return _dir; }
/**
* @return interpolation method ("cubic" or "bilinear").
**********************************************************************/
const std::string Interpolation() const
{ return std::string(_cubic ? "cubic" : "bilinear"); }
/**
* @return estimate of the maximum interpolation and quantization error
* (meters).
*
* This relies on the value being stored in the data file. If the value is
* absent, return &minus;1.
**********************************************************************/
Math::real MaxError() const { return _maxerror; }
/**
* @return estimate of the RMS interpolation and quantization error
* (meters).
*
* This relies on the value being stored in the data file. If the value is
* absent, return &minus;1.
**********************************************************************/
Math::real RMSError() const { return _rmserror; }
/**
* @return offset (meters).
*
* This in used in converting from the pixel values in the data file to
* geoid heights.
**********************************************************************/
Math::real Offset() const { return _offset; }
/**
* @return scale (meters).
*
* This in used in converting from the pixel values in the data file to
* geoid heights.
**********************************************************************/
Math::real Scale() const { return _scale; }
/**
* @return true if the object is constructed to be thread safe.
**********************************************************************/
bool ThreadSafe() const { return _threadsafe; }
/**
* @return true if a data cache is active.
**********************************************************************/
bool Cache() const { return _cache; }
/**
* @return west edge of the cached area; the cache includes this edge.
**********************************************************************/
Math::real CacheWest() const {
return _cache ? ((_xoffset + (_xsize == _width ? 0 : _cubic)
+ _width/2) % _width - _width/2) / _rlonres :
0;
}
/**
* @return east edge of the cached area; the cache excludes this edge.
**********************************************************************/
Math::real CacheEast() const {
return _cache ?
CacheWest() +
(_xsize - (_xsize == _width ? 0 : 1 + 2 * _cubic)) / _rlonres :
0;
}
/**
* @return north edge of the cached area; the cache includes this edge.
**********************************************************************/
Math::real CacheNorth() const {
return _cache ? real(Math::qd) - (_yoffset + _cubic) / _rlatres : 0;
}
/**
* @return south edge of the cached area; the cache excludes this edge
* unless it's the south pole.
**********************************************************************/
Math::real CacheSouth() const {
return _cache ?
real(Math::qd) - ( _yoffset + _ysize - 1 - _cubic) / _rlatres :
0;
}
/**
* @return \e a the equatorial radius of the WGS84 ellipsoid (meters).
*
* (The WGS84 value is returned because the supported geoid models are all
* based on this ellipsoid.)
**********************************************************************/
Math::real EquatorialRadius() const
{ return Constants::WGS84_a(); }
/**
* @return \e f the flattening of the WGS84 ellipsoid.
*
* (The WGS84 value is returned because the supported geoid models are all
* based on this ellipsoid.)
**********************************************************************/
Math::real Flattening() const { return Constants::WGS84_f(); }
///@}
/**
* @return the default path for geoid data files.
*
* This is the value of the environment variable GEOGRAPHICLIB_GEOID_PATH,
* if set; otherwise, it is $GEOGRAPHICLIB_DATA/geoids if the environment
* variable GEOGRAPHICLIB_DATA is set; otherwise, it is a compile-time
* default (/usr/local/share/GeographicLib/geoids on non-Windows systems
* and C:/ProgramData/GeographicLib/geoids on Windows systems).
**********************************************************************/
static std::string DefaultGeoidPath();
/**
* @return the default name for the geoid.
*
* This is the value of the environment variable GEOGRAPHICLIB_GEOID_NAME,
* if set; otherwise, it is "egm96-5". The Geoid class does not use this
* function; it is just provided as a convenience for a calling program
* when constructing a Geoid object.
**********************************************************************/
static std::string DefaultGeoidName();
};
} // namespace GeographicLib
#if defined(_MSC_VER)
# pragma warning (pop)
#endif
#endif // GEOGRAPHICLIB_GEOID_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
GeographicLib::GeographicErr
Exception handling for GeographicLib.
Definition Constants.hpp:316
GeographicLib::Geoid
Looking up the height of the geoid above the ellipsoid.
Definition Geoid.hpp:82
GeographicLib::Geoid::Scale
Math::real Scale() const
Definition Geoid.hpp:380
GeographicLib::Geoid::MaxError
Math::real MaxError() const
Definition Geoid.hpp:355
GeographicLib::Geoid::Description
const std::string & Description() const
Definition Geoid.hpp:319
GeographicLib::Geoid::CacheEast
Math::real CacheEast() const
Definition Geoid.hpp:404
GeographicLib::Geoid::GeoidDirectory
const std::string & GeoidDirectory() const
Definition Geoid.hpp:340
GeographicLib::Geoid::Cache
bool Cache() const
Definition Geoid.hpp:390
GeographicLib::Geoid::Flattening
Math::real Flattening() const
Definition Geoid.hpp:443
GeographicLib::Geoid::RMSError
Math::real RMSError() const
Definition Geoid.hpp:364
GeographicLib::Geoid::GeoidFile
const std::string & GeoidFile() const
Definition Geoid.hpp:329
GeographicLib::Geoid::convertflag
convertflag
Definition Geoid.hpp:179
GeographicLib::Geoid::CacheSouth
Math::real CacheSouth() const
Definition Geoid.hpp:422
GeographicLib::Geoid::CacheAll
void CacheAll() const
Definition Geoid.hpp:259
GeographicLib::Geoid::EquatorialRadius
Math::real EquatorialRadius() const
Definition Geoid.hpp:434
GeographicLib::Geoid::Interpolation
const std::string Interpolation() const
Definition Geoid.hpp:345
GeographicLib::Geoid::CacheNorth
Math::real CacheNorth() const
Definition Geoid.hpp:414
GeographicLib::Geoid::ConvertHeight
Math::real ConvertHeight(real lat, real lon, real h, convertflag d) const
Definition Geoid.hpp:305
GeographicLib::Geoid::Offset
Math::real Offset() const
Definition Geoid.hpp:372
GeographicLib::Geoid::DateTime
const std::string & DateTime() const
Definition Geoid.hpp:324
GeographicLib::Geoid::operator()
Math::real operator()(real lat, real lon) const
Definition Geoid.hpp:285
GeographicLib::Geoid::ThreadSafe
bool ThreadSafe() const
Definition Geoid.hpp:385
GeographicLib::Geoid::GeoidName
const std::string & GeoidName() const
Definition Geoid.hpp:335
GeographicLib::Geoid::CacheWest
Math::real CacheWest() const
Definition Geoid.hpp:395
GeographicLib::Math::real
double real
Definition Math.hpp:110
GeographicLib
Namespace for GeographicLib.
Definition Accumulator.cpp:12