GeographicLib  1.49
Geoid.hpp
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1 /**
2  * \file Geoid.hpp
3  * \brief Header for GeographicLib::Geoid class
4  *
5  * Copyright (c) Charles Karney (2009-2015) <charles@karney.com> and licensed
6  * under the MIT/X11 License. For more information, see
7  * https://geographiclib.sourceforge.io/
8  **********************************************************************/
9 
10 #if !defined(GEOGRAPHICLIB_GEOID_HPP)
11 #define GEOGRAPHICLIB_GEOID_HPP 1
12 
13 #include <vector>
14 #include <fstream>
16 
17 #if defined(_MSC_VER)
18 // Squelch warnings about dll vs vector and constant conditional expressions
19 # pragma warning (push)
20 # pragma warning (disable: 4251 4127)
21 #endif
22 
23 #if !defined(GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH)
24 /**
25  * The size of the pixel data in the pgm data files for the geoids. 2 is the
26  * standard size corresponding to a maxval 2<sup>16</sup>&minus;1. Setting it
27  * to 4 uses a maxval of 2<sup>32</sup>&minus;1 and changes the extension for
28  * the data files from .pgm to .pgm4. Note that the format of these pgm4 files
29  * is a non-standard extension of the pgm format.
30  **********************************************************************/
31 # define GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH 2
32 #endif
33 
34 namespace GeographicLib {
35 
36  /**
37  * \brief Looking up the height of the geoid above the ellipsoid
38  *
39  * This class evaluates the height of one of the standard geoids, EGM84,
40  * EGM96, or EGM2008 by bilinear or cubic interpolation into a rectangular
41  * grid of data. These geoid models are documented in
42  * - EGM84:
43  * http://earth-info.nga.mil/GandG/wgs84/gravitymod/wgs84_180/wgs84_180.html
44  * - EGM96:
45  * http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html
46  * - EGM2008:
47  * http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008
48  *
49  * The geoids are defined in terms of spherical harmonics. However in order
50  * to provide a quick and flexible method of evaluating the geoid heights,
51  * this class evaluates the height by interpolation into a grid of
52  * precomputed values.
53  *
54  * The height of the geoid above the ellipsoid, \e N, is sometimes called the
55  * geoid undulation. It can be used to convert a height above the ellipsoid,
56  * \e h, to the corresponding height above the geoid (the orthometric height,
57  * roughly the height above mean sea level), \e H, using the relations
58  *
59  * &nbsp;&nbsp;&nbsp;\e h = \e N + \e H;
60  * &nbsp;&nbsp;\e H = &minus;\e N + \e h.
61  *
62  * See \ref geoid for details of how to install the data sets, the data
63  * format, estimates of the interpolation errors, and how to use caching.
64  *
65  * This class is typically \e not thread safe in that a single instantiation
66  * cannot be safely used by multiple threads because of the way the object
67  * reads the data set and because it maintains a single-cell cache. If
68  * multiple threads need to calculate geoid heights they should all construct
69  * thread-local instantiations. Alternatively, set the optional \e
70  * threadsafe parameter to true in the constructor. This causes the
71  * constructor to read all the data into memory and to turn off the
72  * single-cell caching which results in a Geoid object which \e is thread
73  * safe.
74  *
75  * Example of use:
76  * \include example-Geoid.cpp
77  *
78  * <a href="GeoidEval.1.html">GeoidEval</a> is a command-line utility
79  * providing access to the functionality of Geoid.
80  **********************************************************************/
81 
83  private:
84  typedef Math::real real;
85 #if GEOGRAPHICLIB_GEOID_PGM_PIXEL_WIDTH != 4
86  typedef unsigned short pixel_t;
87  static const unsigned pixel_size_ = 2;
88  static const unsigned pixel_max_ = 0xffffu;
89 #else
90  typedef unsigned pixel_t;
91  static const unsigned pixel_size_ = 4;
92  static const unsigned pixel_max_ = 0xffffffffu;
93 #endif
94  static const unsigned stencilsize_ = 12;
95  static const unsigned nterms_ = ((3 + 1) * (3 + 2))/2; // for a cubic fit
96  static const int c0_;
97  static const int c0n_;
98  static const int c0s_;
99  static const int c3_[stencilsize_ * nterms_];
100  static const int c3n_[stencilsize_ * nterms_];
101  static const int c3s_[stencilsize_ * nterms_];
102 
103  std::string _name, _dir, _filename;
104  const bool _cubic;
105  const real _a, _e2, _degree, _eps;
106  mutable std::ifstream _file;
107  real _rlonres, _rlatres;
108  std::string _description, _datetime;
109  real _offset, _scale, _maxerror, _rmserror;
110  int _width, _height;
111  unsigned long long _datastart, _swidth;
112  bool _threadsafe;
113  // Area cache
114  mutable std::vector< std::vector<pixel_t> > _data;
115  mutable bool _cache;
116  // NE corner and extent of cache
117  mutable int _xoffset, _yoffset, _xsize, _ysize;
118  // Cell cache
119  mutable int _ix, _iy;
120  mutable real _v00, _v01, _v10, _v11;
121  mutable real _t[nterms_];
122  void filepos(int ix, int iy) const {
123  _file.seekg(
124 #if !(defined(__GNUC__) && __GNUC__ < 4)
125  // g++ 3.x doesn't know about the cast to streamoff.
126  std::ios::streamoff
127 #endif
128  (_datastart +
129  pixel_size_ * (unsigned(iy)*_swidth + unsigned(ix))));
130  }
131  real rawval(int ix, int iy) const {
132  if (ix < 0)
133  ix += _width;
134  else if (ix >= _width)
135  ix -= _width;
136  if (_cache && iy >= _yoffset && iy < _yoffset + _ysize &&
137  ((ix >= _xoffset && ix < _xoffset + _xsize) ||
138  (ix + _width >= _xoffset && ix + _width < _xoffset + _xsize))) {
139  return real(_data[iy - _yoffset]
140  [ix >= _xoffset ? ix - _xoffset : ix + _width - _xoffset]);
141  } else {
142  if (iy < 0 || iy >= _height) {
143  iy = iy < 0 ? -iy : 2 * (_height - 1) - iy;
144  ix += (ix < _width/2 ? 1 : -1) * _width/2;
145  }
146  try {
147  filepos(ix, iy);
148  // initial values to suppress warnings in case get fails
149  char a = 0, b = 0;
150  _file.get(a);
151  _file.get(b);
152  unsigned r = ((unsigned char)(a) << 8) | (unsigned char)(b);
153  if (pixel_size_ == 4) {
154  _file.get(a);
155  _file.get(b);
156  r = (r << 16) | ((unsigned char)(a) << 8) | (unsigned char)(b);
157  }
158  return real(r);
159  }
160  catch (const std::exception& e) {
161  // throw GeographicErr("Error reading " + _filename + ": "
162  // + e.what());
163  // triggers complaints about the "binary '+'" under Visual Studio.
164  // So use '+=' instead.
165  std::string err("Error reading ");
166  err += _filename;
167  err += ": ";
168  err += e.what();
169  throw GeographicErr(err);
170  }
171  }
172  }
173  real height(real lat, real lon) const;
174  Geoid(const Geoid&); // copy constructor not allowed
175  Geoid& operator=(const Geoid&); // copy assignment not allowed
176  public:
177 
178  /**
179  * Flags indicating conversions between heights above the geoid and heights
180  * above the ellipsoid.
181  **********************************************************************/
182  enum convertflag {
183  /**
184  * The multiplier for converting from heights above the geoid to heights
185  * above the ellipsoid.
186  **********************************************************************/
187  ELLIPSOIDTOGEOID = -1,
188  /**
189  * No conversion.
190  **********************************************************************/
191  NONE = 0,
192  /**
193  * The multiplier for converting from heights above the ellipsoid to
194  * heights above the geoid.
195  **********************************************************************/
196  GEOIDTOELLIPSOID = 1,
197  };
198 
199  /** \name Setting up the geoid
200  **********************************************************************/
201  ///@{
202  /**
203  * Construct a geoid.
204  *
205  * @param[in] name the name of the geoid.
206  * @param[in] path (optional) directory for data file.
207  * @param[in] cubic (optional) interpolation method; false means bilinear,
208  * true (the default) means cubic.
209  * @param[in] threadsafe (optional), if true, construct a thread safe
210  * object. The default is false
211  * @exception GeographicErr if the data file cannot be found, is
212  * unreadable, or is corrupt.
213  * @exception GeographicErr if \e threadsafe is true but the memory
214  * necessary for caching the data can't be allocated.
215  *
216  * The data file is formed by appending ".pgm" to the name. If \e path is
217  * specified (and is non-empty), then the file is loaded from directory, \e
218  * path. Otherwise the path is given by DefaultGeoidPath(). If the \e
219  * threadsafe parameter is true, the data set is read into memory, the data
220  * file is closed, and single-cell caching is turned off; this results in a
221  * Geoid object which \e is thread safe.
222  **********************************************************************/
223  explicit Geoid(const std::string& name, const std::string& path = "",
224  bool cubic = true, bool threadsafe = false);
225 
226  /**
227  * Set up a cache.
228  *
229  * @param[in] south latitude (degrees) of the south edge of the cached
230  * area.
231  * @param[in] west longitude (degrees) of the west edge of the cached area.
232  * @param[in] north latitude (degrees) of the north edge of the cached
233  * area.
234  * @param[in] east longitude (degrees) of the east edge of the cached area.
235  * @exception GeographicErr if the memory necessary for caching the data
236  * can't be allocated (in this case, you will have no cache and can try
237  * again with a smaller area).
238  * @exception GeographicErr if there's a problem reading the data.
239  * @exception GeographicErr if this is called on a threadsafe Geoid.
240  *
241  * Cache the data for the specified "rectangular" area bounded by the
242  * parallels \e south and \e north and the meridians \e west and \e east.
243  * \e east is always interpreted as being east of \e west, if necessary by
244  * adding 360&deg; to its value. \e south and \e north should be in
245  * the range [&minus;90&deg;, 90&deg;].
246  **********************************************************************/
247  void CacheArea(real south, real west, real north, real east) const;
248 
249  /**
250  * Cache all the data.
251  *
252  * @exception GeographicErr if the memory necessary for caching the data
253  * can't be allocated (in this case, you will have no cache and can try
254  * again with a smaller area).
255  * @exception GeographicErr if there's a problem reading the data.
256  * @exception GeographicErr if this is called on a threadsafe Geoid.
257  *
258  * On most computers, this is fast for data sets with grid resolution of 5'
259  * or coarser. For a 1' grid, the required RAM is 450MB; a 2.5' grid needs
260  * 72MB; and a 5' grid needs 18MB.
261  **********************************************************************/
262  void CacheAll() const { CacheArea(real(-90), real(0),
263  real(90), real(360)); }
264 
265  /**
266  * Clear the cache. This never throws an error. (This does nothing with a
267  * thread safe Geoid.)
268  **********************************************************************/
269  void CacheClear() const;
270 
271  ///@}
272 
273  /** \name Compute geoid heights
274  **********************************************************************/
275  ///@{
276  /**
277  * Compute the geoid height at a point
278  *
279  * @param[in] lat latitude of the point (degrees).
280  * @param[in] lon longitude of the point (degrees).
281  * @exception GeographicErr if there's a problem reading the data; this
282  * never happens if (\e lat, \e lon) is within a successfully cached
283  * area.
284  * @return the height of the geoid above the ellipsoid (meters).
285  *
286  * The latitude should be in [&minus;90&deg;, 90&deg;].
287  **********************************************************************/
288  Math::real operator()(real lat, real lon) const {
289  return height(lat, lon);
290  }
291 
292  /**
293  * Convert a height above the geoid to a height above the ellipsoid and
294  * vice versa.
295  *
296  * @param[in] lat latitude of the point (degrees).
297  * @param[in] lon longitude of the point (degrees).
298  * @param[in] h height of the point (degrees).
299  * @param[in] d a Geoid::convertflag specifying the direction of the
300  * conversion; Geoid::GEOIDTOELLIPSOID means convert a height above the
301  * geoid to a height above the ellipsoid; Geoid::ELLIPSOIDTOGEOID means
302  * convert a height above the ellipsoid to a height above the geoid.
303  * @exception GeographicErr if there's a problem reading the data; this
304  * never happens if (\e lat, \e lon) is within a successfully cached
305  * area.
306  * @return converted height (meters).
307  **********************************************************************/
308  Math::real ConvertHeight(real lat, real lon, real h,
309  convertflag d) const {
310  return h + real(d) * height(lat, lon);
311  }
312 
313  ///@}
314 
315  /** \name Inspector functions
316  **********************************************************************/
317  ///@{
318  /**
319  * @return geoid description, if available, in the data file; if
320  * absent, return "NONE".
321  **********************************************************************/
322  const std::string& Description() const { return _description; }
323 
324  /**
325  * @return date of the data file; if absent, return "UNKNOWN".
326  **********************************************************************/
327  const std::string& DateTime() const { return _datetime; }
328 
329  /**
330  * @return full file name used to load the geoid data.
331  **********************************************************************/
332  const std::string& GeoidFile() const { return _filename; }
333 
334  /**
335  * @return "name" used to load the geoid data (from the first argument of
336  * the constructor).
337  **********************************************************************/
338  const std::string& GeoidName() const { return _name; }
339 
340  /**
341  * @return directory used to load the geoid data.
342  **********************************************************************/
343  const std::string& GeoidDirectory() const { return _dir; }
344 
345  /**
346  * @return interpolation method ("cubic" or "bilinear").
347  **********************************************************************/
348  const std::string Interpolation() const
349  { return std::string(_cubic ? "cubic" : "bilinear"); }
350 
351  /**
352  * @return estimate of the maximum interpolation and quantization error
353  * (meters).
354  *
355  * This relies on the value being stored in the data file. If the value is
356  * absent, return &minus;1.
357  **********************************************************************/
358  Math::real MaxError() const { return _maxerror; }
359 
360  /**
361  * @return estimate of the RMS interpolation and quantization error
362  * (meters).
363  *
364  * This relies on the value being stored in the data file. If the value is
365  * absent, return &minus;1.
366  **********************************************************************/
367  Math::real RMSError() const { return _rmserror; }
368 
369  /**
370  * @return offset (meters).
371  *
372  * This in used in converting from the pixel values in the data file to
373  * geoid heights.
374  **********************************************************************/
375  Math::real Offset() const { return _offset; }
376 
377  /**
378  * @return scale (meters).
379  *
380  * This in used in converting from the pixel values in the data file to
381  * geoid heights.
382  **********************************************************************/
383  Math::real Scale() const { return _scale; }
384 
385  /**
386  * @return true if the object is constructed to be thread safe.
387  **********************************************************************/
388  bool ThreadSafe() const { return _threadsafe; }
389 
390  /**
391  * @return true if a data cache is active.
392  **********************************************************************/
393  bool Cache() const { return _cache; }
394 
395  /**
396  * @return west edge of the cached area; the cache includes this edge.
397  **********************************************************************/
399  return _cache ? ((_xoffset + (_xsize == _width ? 0 : _cubic)
400  + _width/2) % _width - _width/2) / _rlonres :
401  0;
402  }
403 
404  /**
405  * @return east edge of the cached area; the cache excludes this edge.
406  **********************************************************************/
408  return _cache ?
409  CacheWest() +
410  (_xsize - (_xsize == _width ? 0 : 1 + 2 * _cubic)) / _rlonres :
411  0;
412  }
413 
414  /**
415  * @return north edge of the cached area; the cache includes this edge.
416  **********************************************************************/
418  return _cache ? 90 - (_yoffset + _cubic) / _rlatres : 0;
419  }
420 
421  /**
422  * @return south edge of the cached area; the cache excludes this edge
423  * unless it's the south pole.
424  **********************************************************************/
426  return _cache ? 90 - ( _yoffset + _ysize - 1 - _cubic) / _rlatres : 0;
427  }
428 
429  /**
430  * @return \e a the equatorial radius of the WGS84 ellipsoid (meters).
431  *
432  * (The WGS84 value is returned because the supported geoid models are all
433  * based on this ellipsoid.)
434  **********************************************************************/
436  { return Constants::WGS84_a(); }
437 
438  /**
439  * @return \e f the flattening of the WGS84 ellipsoid.
440  *
441  * (The WGS84 value is returned because the supported geoid models are all
442  * based on this ellipsoid.)
443  **********************************************************************/
445  ///@}
446 
447  /**
448  * @return the default path for geoid data files.
449  *
450  * This is the value of the environment variable GEOGRAPHICLIB_GEOID_PATH,
451  * if set; otherwise, it is $GEOGRAPHICLIB_DATA/geoids if the environment
452  * variable GEOGRAPHICLIB_DATA is set; otherwise, it is a compile-time
453  * default (/usr/local/share/GeographicLib/geoids on non-Windows systems
454  * and C:/ProgramData/GeographicLib/geoids on Windows systems).
455  **********************************************************************/
456  static std::string DefaultGeoidPath();
457 
458  /**
459  * @return the default name for the geoid.
460  *
461  * This is the value of the environment variable GEOGRAPHICLIB_GEOID_NAME,
462  * if set; otherwise, it is "egm96-5". The Geoid class does not use this
463  * function; it is just provided as a convenience for a calling program
464  * when constructing a Geoid object.
465  **********************************************************************/
466  static std::string DefaultGeoidName();
467 
468  };
469 
470 } // namespace GeographicLib
471 
472 #if defined(_MSC_VER)
473 # pragma warning (pop)
474 #endif
475 
476 #endif // GEOGRAPHICLIB_GEOID_HPP
const std::string & GeoidFile() const
Definition: Geoid.hpp:332
Math::real Scale() const
Definition: Geoid.hpp:383
#define GEOGRAPHICLIB_EXPORT
Definition: Constants.hpp:91
Math::real RMSError() const
Definition: Geoid.hpp:367
bool ThreadSafe() const
Definition: Geoid.hpp:388
GeographicLib::Math::real real
Definition: GeodSolve.cpp:31
const std::string Interpolation() const
Definition: Geoid.hpp:348
Math::real Offset() const
Definition: Geoid.hpp:375
const std::string & GeoidName() const
Definition: Geoid.hpp:338
Math::real ConvertHeight(real lat, real lon, real h, convertflag d) const
Definition: Geoid.hpp:308
bool Cache() const
Definition: Geoid.hpp:393
Math::real CacheNorth() const
Definition: Geoid.hpp:417
Math::real MaxError() const
Definition: Geoid.hpp:358
Namespace for GeographicLib.
Definition: Accumulator.cpp:12
const std::string & Description() const
Definition: Geoid.hpp:322
Exception handling for GeographicLib.
Definition: Constants.hpp:389
Math::real CacheSouth() const
Definition: Geoid.hpp:425
Header for GeographicLib::Constants class.
Math::real CacheWest() const
Definition: Geoid.hpp:398
Math::real Flattening() const
Definition: Geoid.hpp:444
const std::string & DateTime() const
Definition: Geoid.hpp:327
const std::string & GeoidDirectory() const
Definition: Geoid.hpp:343
void CacheAll() const
Definition: Geoid.hpp:262
Math::real MajorRadius() const
Definition: Geoid.hpp:435
Math::real CacheEast() const
Definition: Geoid.hpp:407
Math::real operator()(real lat, real lon) const
Definition: Geoid.hpp:288
Looking up the height of the geoid above the ellipsoid.
Definition: Geoid.hpp:82